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GANEX Newsletter No. 83 December 2019

III-N Technology

GaNEX | III-N Technology Newsletter No. 83 | 2

METHODOLOGY

Each month

150+ new scientific publications

200+ new patent applications

30+ new press releases

Sources 10+ scientific journal editors

Elsevier, IOP, IEEE, Wiley, Springer, APS, AIP, AVS, ECS, Nature, Science …

10+ specialist magazines Semiconductor Today, ElectoIQ, i-micronews,

Compound Semiconductor, Solid State Technology … 5+ open access database: FreeFulPDF, DOAJ …

Patent database: Questel-Orbit

Selection by III-N French

experts

GANEX monthly newsletter

GaNEX | III-N Technology Newsletter No. 83 | 3

TABLE OF CONTENTS (clickable links to chapters)

SCIENTIFIC PUBLICATIONS ............................................................................................................................. 4

GROUP 1 - LEDs and Lighting ................................................................................................................................. 4

GROUP 2 - Laser and Coherent Light ................................................................................................................... 13

GROUP 3 - Power Electronics .............................................................................................................................. 17

GROUP 4 - Advanced Electronics and RF ............................................................................................................. 25

GROUP 5 – MEMS and Sensors............................................................................................................................ 31

GROUP 6 - Photovoltaics and Energy harvesting................................................................................................. 36

GROUP 7 - Materials, Technology and Fundamental .......................................................................................... 40

PRESS RELEASE ............................................................................................................................................ 54

PATENT APPLICATIONS ................................................................................................................................ 76

GaNEX | III-N Technology Newsletter No. 83 | 4

SCIENTIFIC PUBLICATIONS Selection of new scientific articles

GROUP 1 - LEDs and Lighting Group leader: Benjamin Damilano (CRHEA-CNRS)

Information selected by Benjamin Damilano and Mathieu Leroux (CRHEA-CNRS)

Fabrication of relaxed InGaN pseudo-substrates

composed of micron-sized pattern arrays with high

fill factors using porous GaN Electrical & Computer Engineering Department, University

of California Santa Barbara, Santa Barbara, CA 93106,

United States of America

Materials Department, University of California Santa

Barbara, Santa Barbara, CA 93106, United States of

America

Semiconductor Science and Technology

https://doi.org/10.1088/1361-6641/ab4372

Fully or partially relaxed micron-sized InGaN patterns

with fill factors up to 69% were demonstrated via

porosification of the underlying GaN:Si layer. The

impact of the porosification etch conditions and the

pattern geometry on the degree of InGaN relaxation

were studied and monitored via high resolution x-ray

diffraction reciprocal space maps. Additionally, a 45

nm redshift in the photoluminescence emission from

In x Ga1−x N/ In y Ga1−y N multi-quantum wells

(MQWs) regrown on bi-axially relaxed InGaN buffer

layers was observed when compared to a co-loaded

reference sample grown on GaN. The longer emission

wavelength was associated with higher indium

incorporation into the InGaN layers deposited on the

InGaN base layers with a lattice constant larger than

GaN, due to the reduced lattice mismatch between

MQW and InGaN base layer, also called

compositional pulling effect.

Review on Optimization and Current Status of

(Al,In)GaN Superluminescent Diodes Institute of High Pressure Physics PAS, Warsaw, Poland

Kyoto University, Kyoto, Japan

TopGaN Ltd., Warsaw, Poland

ECS J. Solid State Sci. Technol.

https://doi.org/10.1149/2.0282001JSS

Superluminescent diodes represent a device type

which can fill the gap between light emitting diodes

(LEDs) and laser diodes. The light generation based

on Amplified Spontaneous Emission promotes high

brilliance of the light source (better than in case of

LEDs), and by this efficient light harnessing e.g.

coupling to optical fibers. At the same time the low

time coherence of the light reduces the interference

effects, unfavorable in applications such as Optical

Coherence Tomography or in direct image projection.

This article reviews the development process and the

current status of nitride superluminescent diodes,

from their first introduction in 2009 until present.

Formation mechanism and separation of the

mesoporous GaN Distributed Bragg reflectors from

sapphire substrate School of Science, Xi'an Polytechnic University, Xi'an,

710048, People's Republic of China

School of Microelectronics, Shandong University, Jinan,

250100, People's Republic of China

Materials Research Express

https://doi.org/10.1088/2053-1591/ab400d

The mesoporous GaN (MP-GaN) Distributed Bragg

reflectors (DBRs) with tunable spectral stop-band

across visible spectrum are fabricated by

electrochemical etching in the neutral solution. The

formation mechanism of MP-GaN layer in the DBR is

first studied via the differential interference contrast

microscopy. Then the self-standing MP-GaN DBR is

first separated from the sapphire substrate via an

annealing technology, and is transferred to a foreign

substrate. The transferred MP-GaN DBR with high

quality presents high reflectivity (>90%) and large

stop-band widths (>100 nm). And the improved

crystalline quality is due to the reduced defect

density and the total stress relaxation of the GaN

film. The high reflectivity and good crystalline quality

render the lift-off MP-GaN DBR a promising

application prospect in flexible optoelectronic

devices.

GaNEX | III-N Technology Newsletter No. 83 | 5

Progress in High Performance III-Nitride Micro-Light-

Emitting Diodes Materials Department, University of California, Santa

Barbara, California 93106, USA

Department of Electrical and Computer Engineering,

University of California, Santa Barbara, California 93106,

USA

ECS J. Solid State Sci. Technol.

https://doi.org/10.1149/2.0302001JSS

The developments of high performance InGaN based

micro-light-emitting diodes (μLEDs) are discussed.

We first review the early demonstrations of μLEDs

and the state-of-the-art outstanding achievements on

the emerging high-quality display and visible-light

communication applications. Due to the miniature

dimensions of μLEDs, the key understandings and the

significant device advancements to achieve excellent

energy efficiency are addressed. Lastly, two other

critical challenges of μLEDs, namely full-color scheme

and mass transfer technique, and their potential

solutions are explored for future investigations.

Active Efficiency as a Key Parameter for

Understanding the Efficiency Droop in InGaN-Based

Light-Emitting Diodes Department of Photonics and Nanoelectronics, Hanyang

University ERICA, Ansan, Gyeonggi-do 15588, Korea

Department of Electronics and Communication

Engineering, Hanyang University ERICA, Ansan, Gyeonggi-

do 15588, Korea

EtaMax Co. Ltd., Suwon, Gyeonggi-do 16648, Korea

ECS J. Solid State Sci. Technol.

https://doi.org/10.1149/2.0312001JSS

In this paper, we aim to understand the

interrelationships between current, voltage, radiant

power, and eventually, the power efficiency (PE) of

InGaN-based blue light-emitting diodes (LEDs) at high

injection currents. For this purpose, we first

summarize the terms and definitions of various LED

efficiencies. It is essential to measure each efficiency

to understand the physics behind the LED operation

and improve the device performance further. Here,

we show how to measure various LED efficiencies

with physically measurable quantities of the radiant

power, current, voltage, and spectrum of the LED

device. Both the internal quantum efficiency (IQE)

and the voltage efficiency (VE) are interrelated with

the carrier recombination processes. The newly

introduced active efficiency (AE) captures the effects

of the active-layer quality on the IQE and the VE

simultaneously. A novel method of measuring the IQE

just at room temperature, so-called the room-

temperature reference-point method, enables the

measurement of the IQEs of many LED chips,

highlighting the importance of the AE. Using the

experimental IQE curve, it is possible to separate the

total injection current into the radiative and

nonradiative recombination currents. A trade-off

relationship between the IQE and the VE and its

common origins are revealed by this approach.

Recent Advances and Challenges in Indium Gallium

Nitride (InxGa1-xN) Materials for Solid State Lighting Department of Physics, Government Degree College for

Women, Kathua, Jammu and Kashmir-184102, India

Department of Physics, University of Jammu, Jammu and

Kashmir-180006, India

Department of Mechanical System Engineering, Graduate

School of Science and Engineering, Yamagata University,

Yonezawa, Yamagata 992-8510, Japan

ECS J. Solid State Sci. Technol.

https://doi.org/10.1149/2.0292001JSS

In recent times, the demand for electrical energy is

increased to such an extent that the scientific

research has to be focused on the development of

materials that fulfil the growing demands of energy

for efficient solid state lighting purposes and provide

clean and green energy to mitigate the alarming

effects of climate change. The ternary Indium Gallium

Nitride (InxGa1-xN) alloys have emerged as the

potential candidate for Solid State lighting as they

inherent such attributes that make them capable for

these applications. In this review, the attributes of

InxGa1-xN alloys have been discussed. The

dependence of bandgap and bowing parameter on

the composition of InxGa1-xN alloys along with

various techniques employed for the growth of these

alloys in bulk and nanostructure forms have been

reviewed. The recent advances in InxGa1-xN based

nanostructures for Solid State lighting have also been

extensively reviewed. The challenges that are to be

overcome for potential use of InxGa1-xN alloys like

phase segregation, unavailability of a suitable

GaNEX | III-N Technology Newsletter No. 83 | 6

substrate, polarization and doping have been

thoroughly highlighted. In the end, the conclusion

and future scope of work on these wonderful classes

of materials has been drawn.

An Enhancement Mode MOSFET Based on GaN-on-

Silicon Platform for Monolithic OEIC Grünberg Research Centre, Nanjing University of Posts and

Telecommunications, Nanjing 210003, China

IEEE Electron Device Letters

https://doi.org/10.1109/LED.2019.2952905

This letter proposes an enhancement mode MOSFET

on GaN-on-silicon LED epitaxial wafer for the first

time. The fabrication processes of the MOSFET are

fully compatible with InGaN/GaN multiple-quantum-

wells (MQWs) diode and include no ion implantation

or additional epitaxial growth. Gate-recess structure

is formed by well-controlled etching to define the

channel area. The bottom and side wall of the recess

are fully covered by the gate metal to improve the

control ability of gate voltage on the channel

conductance. The measurement results indicate

acceptable performance of the MOSFET with

threshold voltage of 6.01 V. Finally, the MOSFET is

serially connected with an LED based on the same

platform and the brightness of LED can be effectively

controlled by the gate voltage according to the

experimental results. Therefore the MOSFET and LED

have been fabricated on the same GaN-on-silicon

platform, which paves way for the monolithic optical

electronic integrated circuit (OEIC).

Improved Reverse Leakage Current in GaInN-based

LEDs with a Sputtered AlN Buffer Layer Faculty of Science and Technology, Meijo University,

Nagoya 468-8502, Japan

Akasaki Research Center, Nagoya University, Nagoya 464-

8603, Japan

IEEE Photonics Technology Letters

https://doi.org/10.1109/LPT.2019.2952106

In this study, the improvement of reverse leakage

current characteristics with a sputtered (SP) -AlN

buffer layer in GaInN-based green light-emitting

diodes (LEDs) has been presented for the first time.

To understand the origin of the improvement, a

detailed review and careful analysis of reverse

leakage current characteristics were performed. The

review and analysis identified that the improvement

was primarily caused by the suppression of variable-

range-hopping process obtained by replacing

conventional low-temperature GaN buffer.

Verification that threading dislocations and V-defects

can enhance the variable-range-hopping process has

been received. We believe that this study will

contribute to the realization of green LEDs with

advantages of high reliability, a long lifetime, and

electrical robustness.

Evidence of trap-assisted Auger recombination in

low radiative efficiency MBE-grown III-nitride LEDs Department of Materials, University of California, Santa

Barbara, California 93106-5050, USA

Department of Applied Physics, KTH Royal Institute of

Technology, Electrum 229, 16440 Kista, Sweden

Laboratoire de Physique de la Matière Condensée, CNRS,

Ecole Polytechnique, IP Paris, 91128 Palaiseau, France

Journal of Applied Physics

https://doi.org/10.1063/1.5096773

By studying low radiative efficiency blue III-nitride

light emitting diodes (LEDs), we find that the ABC

model of recombination commonly used for

understanding efficiency behavior in LEDs is

insufficient and that additional effects should be

taken into account. We propose a modification to the

standard recombination model by incorporating a

bimolecular nonradiative term. The modified model is

shown to be in much better agreement with the

radiative efficiency data and to be more consistent

than the conventional model with very short carrier

lifetimes measured by time-resolved

photoluminescence in similar, low radiative efficiency

material. We present experimental evidence that a

hot carrier-generating process is occurring within

these devices, in the form of measurements of

forward photocurrent under forward bias. The

forward photocurrent, due to hot carrier generation

in the active region, is present despite the lack of any

“efficiency droop”—the usual signature of band-to-

band Auger recombination in high-quality III-nitride

LEDs. Hot carrier generation in the absence of band-

to-band Auger recombination implies that some

other source of hot carriers exists within these low

GaNEX | III-N Technology Newsletter No. 83 | 7

radiative efficiency devices, such as trap-assisted

Auger recombination.

Effect of KOH passivation for top-down fabricated

InGaN nanowire light emitting diodes Department of Microsystems Engineering, Rochester

Institute of Technology, Rochester, New York 14623, USA

Department of Electrical and Microelectronic Engineering,

Rochester Institute of Technology, Rochester, New York

14623, USA

Journal of Applied Physics

https://doi.org/10.1063/1.5123171

Gallium nitride (GaN) nanowire (NW) light emitting

diodes (LEDs) are promising candidates for

microdisplay applications due to smaller dimensions

and potential for novel integration approaches. For

the commonly adopted top-down GaN NW

fabrication, the required dry etching steps tend to

result in surface states, leading to reduced radiative

recombination rates in LEDs. To passivate the surface

and tune the diameter of the NWs, hydroxyl-based

chemicals such as potassium hydroxide (KOH) are

widely used to treat the surface of these

nanostructures. However, studies on the effects of

temperature, concentration, and the damage

recovery aspects of hydroxyl etching of GaN NWs are

very scarce. These etching parameters are of great

importance for device performance. Here, these

effects are explored thoroughly with a focus on the

correlation of InGaN/GaN NW LED performances to

KOH etching temperature, concentration, and time,

together with a fundamental crystallographic

analysis. The KOH concentration resulting in total

removal of the NW base tapering and a collimated

etch profile for InGaN NW LEDs was found to be

0.8 wt. % at a temperature of 45 °C. A 20 min etch at

23 °C with a 0.1 wt. % KOH concentration will remove

surface states from a top-down fabricated NW LED to

recover up to 90% of the peak photoluminescence

(PL) intensity lost by the dry etch step. The oscillation

behavior in PL intensity with regard to the KOH etch

time has been demonstrated in InGaN/GaN NW LEDs

for the first time, which will shed light upon the

design and passivation of these devices for

microdisplays.

High-Bandwidth InGaN Self-Powered Detector

Arrays toward MIMO Visible Light Communication

Based on Micro-LED Arrays Institute for Electric Light Sources, School of Information

Science and Technology, Engineering Research Center of

Advanced Lighting Technology, and Academy of

Engineering and Technology, Fudan University, Shanghai

200433, China

Department of Chemistry, University of Toronto, 80 Saint

George Street, Toronto, Ontario M5S 3H6, Canada

ACS Photonics

https://doi.org/10.1021/acsphotonics.9b00799

This work reports the use of the chip-based GaN-

based micro-LED (μLED) arrays for multifunctional

applications as microdisplay, data transmitters,

photodetectors, and solar cells. The functions of

display and transmitter have been reported, and

particularly, we experimentally demonstrated that

μLED arrays could be used as self-powered, high-

performance, and wavelength-selective

photodetectors (PDs), enabling high-speed multiple-

input multiple-output (MIMO) visible light

communications (VLC) under on–off keying (OOK)

modulation scheme using 405 nm violet laser diodes

(LDs) as transmitters. The optoelectronic and

communication characteristics of the μLED-based PDs

with diameters of 40, 60 and 100 μm were

systematically studied. The optoelectronic analysis

shows superior performances of μLED-based PDs at a

405 nm wavelength compared with other previously

reported GaN-based PDs. Under a bias voltage of −5

V, the comparable peak responsivities of 0.27, 0.31,

and 0.24 A/W, specific detectivities of 1.1 × 1011, 2.3

× 1012, and 2.1 × 1012 cm H1/2 W–1, and linear

dynamic ranges (LDRs) of 152, 162, and 164 dB were

achieved for 40, 60, and 100 μm μLEDs, respectively.

Even at zero-bias, that is, self-powered mode, we

have achieved high peak responsivities of 0.24, 0.29,

and 0.21 A/W, high specific detectivities of 7.5 ×

1012, 1.5 × 1013, and 1.3 × 1013 cm H1/2 W–1, and

high LDR up to 186, 196, and 197 dB for 40, 60, and

100 μm μLEDs, respectively. The μLEDs could also be

used to harvest the optical energy of the system,

working as solar cells. The μLED-based PD arrays

were tested as receivers in the VLC system to

implement high-speed parallel communication, which

yields maximum data rates of 180, 175, and 185

GaNEX | III-N Technology Newsletter No. 83 | 8

Mbps for single 40, 60, and 100 μm μLED-based PDs

at a distance of 1 m with BERs of 3.5 × 10–3, 3.7 ×

10–3, and 3.5 × 10–3, respectively. Furthermore, the

2 × 2 MIMO parallel VLC system was achieved to

increase the VLC data rate, which suggests the

potential of using large μLED-based PD arrays for

multiple Gbps and even Tbps VLC applications.

Heteroepitaxial Growth of High-Quality and Crack-

Free AlN Film on Sapphire Substrate with

Nanometer-Scale-Thick AlN Nucleation Layer for

AlGaN-Based Deep Ultraviolet Light-Emitting Diodes Center for Photonics and Semiconductors, School of Power

and Mechanical Engineering, Wuhan University, Wuhan

430072, China

HC SemiTek Corporation, Suzhou 215600, China

The Institute of Technological Sciences, Wuhan University,

Wuhan 430072, China

Nanomaterials

https://doi.org/10.3390/nano9111634

High-quality and crack-free aluminum nitride (AlN)

film on sapphire substrate is the foundation for high-

efficiency aluminum gallium nitride (AlGaN)-based

deep ultraviolet light-emitting diodes (DUV LEDs). We

reported the growth of high-quality and crack-free

AlN film on sapphire substrate with a nanometer-

scale-thick AlN nucleation layer (NL). Three kinds of

nanometer-scale-thick AlN NLs, including in situ low-

temperature AlN (LT-AlN) NL, oxygen-undoped ex situ

sputtered AlN NL, and oxygen-doped ex situ

sputtered AlN NL, were prepared for epitaxial growth

of AlN films on sapphire substrates. The influence of

nanoscale AlN NL thickness on the optical

transmittance, strain state, surface morphology, and

threading dislocation (TD) density of the grown AlN

film on sapphire substrate were carefully

investigated. The average optical transmittance of

AlN film on sapphire substrate with oxygen-doped

sputtered AlN NL was higher than that of AlN films on

sapphire substrates with LT-AlN NL and oxygen-

undoped sputtered AlN NL in the 200–270 nm

wavelength region. However, the AlN film on

sapphire substrate with oxygen-undoped sputtered

AlN NL had the lowest TD density among AlN films on

sapphire substrates. The AlN film on sapphire

substrate with the optimum thickness of sputtered

AlN NL showed weak tensile stress, a crack-free

surface, and low TD density. Furthermore, a 270-nm

AlGaN-based DUV LED was grown on the high-quality

and crack-free AlN film. We believe that our results

offer a promising and practical route for obtaining

high-quality and crack-free AlN film for DUV LED.

High Temperature and Power Dependent

Photoluminescence Analysis on Commercial Lighting

and Display LED Materials for Future Power

Electronic Modules Department of Electrical Engineering, University of

Arkansas, Fayetteville, Arkansas, 72701, USA

HC SemiTek (Suzhou), 28 Chenfeng Road, Zhangjiagang,

Jiangsu, 215600, P.R. China

Sandia National Laboratories, Albuquerque, New Mexico,

87185, USA

School of Electrical, Computer and Energy Engineering,

Arizona State University, Phoenix, Arizona, USA

Scientific Reports

https://doi.org/10.1038/s41598-019-52126-4

Commercial light emitting diode (LED) materials -

blue (i.e., InGaN/GaN multiple quantum wells

(MQWs) for display and lighting), green (i.e.,

InGaN/GaN MQWs for display), and red (i.e.,

Al0.05Ga0.45In0.5P/Al0.4Ga0.1In0.5P for display) are

evaluated in range of temperature (77–800) K for

future applications in high density power electronic

modules. The spontaneous emission quantum

efficiency (QE) of blue, green, and red LED materials

with different wavelengths was calculated using

photoluminescence (PL) spectroscopy. The

spontaneous emission QE was obtained based on a

known model so-called the ABC model. This model

has been recently used extensively to calculate the

internal quantum efficiency and its droop in the III-

nitride LED. At 800 K, the spontaneous emission

quantum efficiencies are around 40% for blue for

lighting and blue for display LED materials, and it is

about 44.5% for green for display LED materials. The

spontaneous emission QE is approximately 30% for

red for display LED material at 800 K. The advance

reported in this paper evidences the possibility of

improving high temperature optocouplers with an

operating temperature of 500 K and above.

GaNEX | III-N Technology Newsletter No. 83 | 9

Thermal droop in high-quality InGaN LEDs Soraa, Inc., 6500 Kaiser Dr., Fremont, California 94555,

USA

Applied Physics Letters

https://doi.org/10.1063/1.5124123

Thermal droop is investigated in high-quality InGaN

light-emitting diodes (LEDs). To determine whether it

is caused by intrinsic variations in recombination or

by transport effects, photoluminescence and

electroluminescence measurements are compared.

The former does not show signs of pronounced

thermal droop, with a near-constant internal

quantum efficiency and recombination lifetime,

regardless of temperature. In contrast, strong

thermal droop is observed in the latter, pointing to

transport effects as a leading contributor. Finally,

high-efficiency LEDs with near-ideal thermal droop

are demonstrated.

AlN overgrowth of nano-pillar-patterned sapphire

with different offcut angle by metalorganic vapor

phase epitaxy Ferdinand-Braun-Institut, Leibniz-Institut fuer

Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489

Berlin, Germany

Centre of Nanoscience & Nanotechnology, University of

Bath, Bath, BA2 7AY, UK

Department of Electronic and Electrical Engineering,

University of Bath, Bath, BA2 7AY, UK

Institute of Solid State Physics, Technical University Berlin,

Hardenbergstr. 36, 10623 Berlin, Germany

Leibniz-Institut fuer Kristallzuechtung, Max-Born-Str. 2,

12489 Berlin, Germany

Department of Physics, SUPA, University of Strathclyde,

107 Rottenrow East, Glasgow G4 0NG, UK

Journal of Crystal Growth

https://doi.org/10.1016/j.jcrysgro.2019.125343

We present overgrowth of nano-patterned sapphire

with different offcut angles by metalorganic vapor

phase epitaxy. Hexagonal arrays of nano-pillars were

prepared via Displacement Talbot Lithography and

dry-etching. 6.6 µm crack-free and fully coalesced AlN

was grown on such substrates. Extended defect

analysis comparing X-ray diffraction, electron

channeling contrast imaging and selective defect

etching revealed a threading dislocation density of

about 109 cm-2. However, for c-plane sapphire offcut

of 0.2° towards m direction the AlN surface shows

step bunches with a height of 10 nm. The detrimental

impact of these step bunches on subsequently grown

AlGaN multi-quantum-wells is investigated by

cathodoluminescence and transmission electron

microscopy. By reducing the sapphire offcut to 0.1°

the formation of step bunches is successfully

suppressed. On top of such a sample an AlGaN-based

UVC LED heterostructure is realized emitting at 265

nm and showing an emission power of 0.81 mW at 20

mA (corresponds to an external quantum efficiency

of 0.86 %).

Defect-Tolerant Luminescent Properties of Low InN

Mole Fraction InxGa1-xN Quantum Wells under the

Presence of Polarization Fields Institute of Multidisciplinary Research for Advanced

Materials, Tohoku University, Sendai, Miyagi 980-8577,

Japan

ECS J. Solid State Sci. Technol.

https://doi.org/10.1149/2.0382001JSS

Different from the case of GaN or AlGaN alloys, the

near-band-edge (NBE) emission of quantum wells

(QWs) and even epilayers of InxGa1-xN alloys of low

InN mole fractions (x) exhibits high quantum-

efficiency (QE) against the presence of threading

dislocations (TDs) as high as 109 cm−2. Accordingly

InxGa1-xN alloys are exclusively used as an active

region of green to ultraviolet light-emitting diodes

(LEDs) and laser diodes, as well as the heart of white

LEDs. Here, current understandings on the emission

mechanisms of InxGa1-xN QWs, especially the defect-

tolerant emission probability of localized excitons,

are reviewed. There exist three disadvantages in

obtaining high QE, namely a high density of TDs that

cause the nonradiative recombination, kinetic

immiscibility of In-containing alloys that introduces

high-concentration Shockley-Read-Hall nonradiative

recombination centers (NRCs) consisting of vacancy

complexes, and high internal electric-fields across the

QWs induced by the polarization discontinuities at

heterointerfaces along the c-axis, which decrease the

radiative recombination rate. The use of InxGa1-xN

alloys of low x overcomes such disadvantages with

the aid of In-originated localization effects that

prevent excitons from trapping by TDs or NRCs.

GaNEX | III-N Technology Newsletter No. 83 | 10

Simultaneous observation of short diffusion length

and sufficiently long nonradiative recombination

lifetime at room temperature indicates strong

localization of holes or excitons.

Characteristics of Blue GaN/InGaN Quantum-Well

Light-Emitting Transistor Graduate Institute of Photonics and Optoelectronics,

National Taiwan University, Taipei 10617, Taiwan

Research and Development Center, Epistar Corporation,

Hsinchu 30078, Taiwan

Department of Photonics, National Chiao-Tung University,

Hsinchu 30010, Taiwan

Research Center for Applied Sciences, Academia Sinica,

Taipei 11529, Taiwan

Department of Electrical Engineering, Graduate Institute of

Photonics and Optoelectronics, National Taiwan

University, Taipei 10617, Taiwan.

IEEE Electron Device Letters

https://doi.org/10.1109/LED.2019.2955733

We demonstrate simultaneous electrical and optical

modulations of the first GaN/InGaN quantum-well

light-emitting transistor (QW-LET) which contains an

In0.15Ga0.85N QW in the heavily p-doped

In0.05Ga0.95N base. Unlike GaAs/InGaAs

counterparts, the GaN/InGaN QW-LET has a current

gain (up to 5) and optical power which increase

linearly with the base current. Its emission spectra

are centered at a wavelength of 420 nm and barely

shift with the current injection, in contrast to the

behavior of typical nitride-based LEDs. The unusual

features of this device may be related to the tilted

band profile induced by the polarization field in the

QW and issue of p-type doping.

Visible LEDs: More than Efficient Light OSRAM Opto Semiconductors GmbH, 93055 Regensburg,

Germany

ECS J. Solid State Sci. Technol.

https://doi.org/10.1149/2.0402001JSS

The lighting sector has seen a tremendous technology

revolution in the recent few decades. This process

has been fueled by light emitting diodes (LEDs), when

group-III nitride materials became available for

semiconductor devices by groundbreaking

technological discovery of p-type conductivity in

gallium nitride (GaN). Ever since this Nobel prize

winning discovery, the race of improving the

efficiency and the efficacy of visible LEDs has been

the dominant driving force, enabled by novel designs

and processes to exploit novel materials, to improve

material quality, electrical and thermal resistance,

light extraction and beam shaping. Technology trends

like miniaturization and integration of electronics and

photonics have led LED markets to expand to a

variety of novel application fields, such as

illumination, sensing, healthcare and visualization,

that are far beyond the traditional general lighting

market. Integration of LEDs and other electronic

devices like CMOS transistor or photodiodes adds

novel functionalities in the smallest dimensions.

Performance improvement of AlGaN-based deep

ultraviolet light-emitting diodes with step-like

quantum barriers School of Microelectronics, University of Science and

Technology of China, Hefei, Anhui 230026, People’s

Republic of China

School of Engineering, University of California San Diego,

San Diego, CA 92093, United States of America

Wuhan National Laboratory for Optoelectronics, Huazhong

University of Science and Technology, Wuhan 430074,

China

IEEE Journal of Quantum Electronics

https://doi.org/10.1109/JQE.2019.2956344

AlGaN-based deep ultraviolet light-emitting diodes

(DUV LEDs) still confront many challenges, which is

partially limited by the poor carrier injection in the

active region. Although incorporating a high Al-

composition quantum barrier (QB) may boost carrier

confinement capability, it will aggravate the quantum

confined Stark effect (QCSE) and thus deteriorate the

optical performance. In this work, a DUV LED

structure with step-like QBs has been proposed and

carefully investigated. This unique QB structure

suppresses the electron overflow into the p-side of

the device and benefits the hole injection efficiency

simultaneously, thereby promoting the radiative

recombination rate in the active region. As a result,

the internal quantum efficiency (IQE) and light output

power (LOP) of the DUV LED with step-like QBs are

significantly improved with an enhancement factor of

40% under 60 mA current injection. Therefore, our

GaNEX | III-N Technology Newsletter No. 83 | 11

step-like QB design provides a feasible approach to

the enhancement of the optical performance of DUV

LEDs.

What limits the efficiency of GaN-based

superluminescent light-emitting diodes (SLEDs)? NUSOD Institute LLC, Newark, USA

Optical and Quantum Electronics

https://doi.org/10.1007/s11082-019-2106-3

Gallium-nitride-based SLEDs are attractive light

sources for augmented reality displays and other

applications. However, the electrical-to-optical power

conversion efficiency (PCE) of SLEDs is still far below

the record-high values reported for LEDs. Utilizing

advanced numerical device simulation, this paper

investigates the internal physical processes that

cause the low PCE of SLEDs. The poor hole

conductivity strongly reduces the electrical efficiency,

similar to laser diodes. However, in contrast to laser

diodes, the rising carrier density in the active layers is

identified as main reason for enhanced Auger

recombination that severely limits the internal

quantum efficiency. Design improvement options are

demonstrated.

Internal quantum efficiencies of AlGaN quantum

dots grown by molecular beam epitaxy and emitting

in the UVA to UVC ranges Université Côte d’Azur, CNRS, CRHEA, 06560 Valbonne,

France

CNRS-Université Montpellier 2, L2C, UMR 5221, 34095

Montpellier, France

Journal of Applied Physics

https://doi.org/10.1063/1.5115593

AlyGa1−yN quantum dots (QDs) have been grown by

molecular beam epitaxy on AlxGa1−xN (0001) using a

2-dimensional–3-dimensional growth mode

transition that leads to the formation of QDs. QDs

have been grown for Al compositions y varying

between 10% and 40%. The influence of the active

region design [composition y, QD height, and

bandgap difference (ΔEg) between the AlxGa1−xN

cladding layer and the AlyGa1−yN QDs] is discussed

based on microscopy, continuous wave

photoluminescence (PL), and time-resolved PL (TRPL)

measurements. In particular, increasing y leads to a

shift of the QD emission toward shorter wavelengths,

allowing covering a spectral range in the UV from

332 nm (UVA) to 276 nm (UVC) at room temperature

(RT). The low-temperature (LT) internal quantum

efficiency of the QD ensembles was estimated from

TRPL experiments at 8 K and values between 11% and

66% were deduced. The highest internal quantum

efficiency (IQE)-LT is found for the QDs with higher Al

content y. Then, the PL spectrally integrated intensity

ratios between RT and LT were measured to estimate

the IQE of the samples at RT. The PL ratio is higher for

larger ΔEg, for QDs with y of 0.1 or 0.2, and high PL

intensity ratios up to 30% were also measured for

QDs with larger y of 0.3 and 0.4. RT IQE values

between 5% and 20% are deduced for AlyGa1−yN

QDs emitting in the 276–308 nm range.

Transferable GaN Enabled by Selective Nucleation of

AlN on Graphene for High‐Brightness Violet

Light‐Emitting Diodes The State Key Discipline Laboratory of Wide Band Gap

Semiconductor Technology, Shaanxi Joint Key Laboratory

of Graphene, Xidian University, Xi’an 710071, China

Advanced Optical Materials

https://doi.org/10.1002/adom.201901632

A transferable GaN epilayer is grown on an improved

aluminum nitride (AlN)/graphene composite

substrate. In this study, theoretical calculations using

first‐principles calculations based on density

functional theory are carefully conducted to further

examine the formation mechanism of AlN on

graphene. AlN selectively grows on graphene via its

optimal nucleation site, which leads to the selective

nucleation of AlN on graphene via quasi‐van der

Waals epitaxy. Thus, an AlN composite nucleation

layer is innovatively inserted between graphene and

GaN, using the time‐distributed and

constant‐pressure growth method by metal organic

chemical vapor deposition. Moreover, a high‐quality

GaN epilayer can be grown while ensuring the

successful exfoliation of GaN by overcoming weak

van der Waals forces between the graphene and the

epilayer. The as‐fabricated violet light‐emitting

diodes (LEDs) deliver an ultrahigh light output power.

This method demonstrates the possibility of

achieving a high‐quality vertical structure for LEDs

GaNEX | III-N Technology Newsletter No. 83 | 12

and the ability to mechanically transfer to achieve

flexible lighting.

Enhanced Performance of AlGaN-Based Deep

Ultraviolet Light-Emitting Diodes with Chirped

Superlattice Electron Deceleration Layer Wuhan National Laboratory for Optoelectronics, Huazhong

University of Science and Technology, Wuhan, China

Nanoscale Research Letters

https://doi.org/10.1186/s11671-019-3201-x

AlGaN-based deep ultraviolet (DUV) light-emitting

diodes (LEDs) suffer from electron overflow and

insufficient hole injection. In this paper, novel DUV

LED structures with superlattice electron deceleration

layer (SEDL) is proposed to decelerate the electrons

injected to the active region and improve radiative

recombination. The effects of several chirped SEDLs

on the performance of DUV LEDs have been studied

experimentally and numerically. The DUV LEDs have

been grown by metal-organic chemical vapor

deposition (MOCVD) and fabricated into

762 × 762 μm2 chips, exhibiting single peak emission

at 275 nm. The external quantum efficiency of 3.43%

and operating voltage of 6.4 V are measured at a

forward current of 40 mA, indicating that the wall-

plug efficiency is 2.41% of the DUV LEDs with

ascending Al-content chirped SEDL. The mechanism

responsible for this improvement is investigated by

theoretical simulations. The lifetime of the DUV LED

with ascending Al-content chirped SEDL is measured

to be over 10,000 h at L50, due to the carrier

injection promotion.

GaNEX | III-N Technology Newsletter No. 83 | 13

GROUP 2 - Laser and Coherent Light Group leader: Bruno Gayral (CEA)

Information selected by Knowmade

Ultrahigh Q microring resonators using a single-

crystal aluminum-nitride-on-sapphire platform Department of Electrical Engineering and Computer

Science, University of Michigan, Ann Arbor, Michigan

48105, USA

Raytheon BBN Technologies, Cambridge, Massachusetts

02138, USA

Optics Letters

https://doi.org/10.1364/OL.44.005679

Aluminum-nitride-on-sapphire has recently emerged

as a novel low-loss photonics platform for a variety of

on-chip electro-optics as well as linear and nonlinear

optics applications. In this Letter, we demonstrate

ultrahigh quality factor (Qint) microring resonators

using single-crystal aluminum nitride grown on a

sapphire substrate with an optimized design and

fabrication process. A record high intrinsic Qint up to

2.8×106 at the wavelength of 1550 nm is achieved

with a fully etched structure, indicating a low

propagation loss less than 0.13 dB/cm. Such high Qint

aluminum-nitride-on-sapphire resonators with their

wide bandgap and electro-optical and nonlinear

optical properties is promising for a wide range of

low-power and high-power compact on-chip

applications over a broad spectral range.

Realization of GaN-based gain-guided blue laser

diodes by helium ion implantation School of Materials Science and Engineering, Shanghai

University, Shanghai 201900, People's Republic of China

Suzhou Institute of Nano-tech and Nano-bionics, Chinese

Academy of Sciences, Suzhou 215123, People's Republic of

China

Key Laboratory of Nanodevices and Applications, Chinese

Academy of Sciences, Suzhou 215123, People's Republic of

China

Semiconductor Science and Technology

https://doi.org/10.1088/1361-6641/ab429c

The fabrication process and characteristics of gallium

nitride (GaN) based gain-guided blue laser diodes

(LDs) are studied, in which an ion implantation

process is adopted to confine carrier injection into

the active region. The implantation of helium ions

with an energy of 85 keV, an angle of 0°, and a

dosage of 4.7 × 1014 cm−2 is conducted in the

experiment. The specific contact resistivity of p-type

ohmic contact of implanted sample is determined to

be 2.2 × 10–4 Ω cm2, which is comparable with the

un-implanted sample. Then, both ion-implanted gain-

guided and ridge waveguide LDs are fabricated at the

same time. Similar threshold current density and

slope efficiency are obtained, while the operation

voltage of ion-implanted gain-guided LDs is 0.2 V

lower than the ridge waveguide LDs at 0.56 kA cm−2.

The ridge waveguide LDs show multi-mode operation

after lasing. However, for ion-implanted gain-guided

LDs, the far-field pattern indicates a single lateral

mode operation up to twice of the threshold current,

and the peak optical output power of blue single

mode LDs at 450 nm exceeds 200 mW under pulsed

condition.

Material gain engineering in staggered polar

AlGaN/AlN quantum wells dedicated for deep UV

lasers Institute of Physics, Wroclaw University of Technology,

Wroclaw, Dolnoslaskie Poland 50-370

IEEE Journal of Selected Topics in Quantum Electronics

https://doi.org/10.1109/JSTQE.2019.2950802

Material gain is calculated for polar staggered

AlxGa1-xN/AlN quantum wells (QWs) of various

architectures: i) with a step-like AlyGa1-yN barrier

grown prior the AlxGa1-xN QW, ii) with a step-like

barrier grown on the QW, and iii) with a step-like

barrier grown prior and on the QW. The obtained

results are compared with those obtained for

reference AlxGa1-xN/AlN QWs. With the increase in

Al concentration in the reference QW the gain peak

blueshifts and its strength decreases mainly due to

the Al-related increase in the electron effective mass.

The step-like barrier is able to tune the spectral

position of the gain peak and enhance the gain

strength. For the staggered QWs with step-like

GaNEX | III-N Technology Newsletter No. 83 | 14

barriers grown prior to the QW a blueshift of the gain

peak is observed while a redshift of the gain peak is

observed for QWs with the step-like barrier grown on

the QW. It is shown that a strong material gain in the

260-280 nm spectral range can be achieved with the

staggered AlxGa1-xN/AlN QW with x=30% and 1 nm

thick step-like AlyGa1-yN barrier of high Al

concentration (y=0.7-0.9).

Spectral tomographic imaging with aplanatic

metalens National Laboratory of Solid State Microstructures, Key

Laboratory of Intelligent Optical Sensing and Integration,

Jiangsu Key Laboratory of Artificial Functional Materials,

College of Engineering and Applied Sciences, Nanjing

University, Nanjing, 210093, China

Collaborative Innovation Center of Advanced

Microstructures, Nanjing, China

Research Center for Applied Sciences, Taipei, 11529,

Taiwan, China

Department of Physics, Taiwan University, Taipei, 10617,

Taiwan, China

Graduate Institute of Electronics Engineering, Taiwan

University, Taipei, 10617, Taiwan, China

Light: Science & Applications

https://doi.org/10.1038/s41377-019-0208-0

Tomography is an informative imaging modality that

is usually implemented by mechanical scanning,

owing to the limited depth-of-field (DOF) in

conventional systems. However, recent imaging

systems are working towards more compact and

stable architectures; therefore, developing

nonmotion tomography is highly desirable. Here, we

propose a metalens-based spectral imaging system

with an aplanatic GaN metalens (NA = 0.78), in which

large chromatic dispersion is used to access spectral

focus tuning and optical zooming in the visible

spectrum. After the function of wavelength-switched

tomography was confirmed on cascaded samples,

this aplanatic metalens is utilized to image

microscopic frog egg cells and shows excellent

tomographic images with distinct DOF features of the

cell membrane and nucleus. Our approach makes

good use of the large diffractive dispersion of the

metalens and develops a new imaging technique that

advances recent informative optical devices.

A 271.8 nm deep-ultraviolet laser diode for room

temperature operation Innovative Devices R&D Center, Corporate Research &

Development, Asahi Kasei Corporation, Fuji, Shizuoka 416-

8501, Japan

Center for Integrated Research of Future Electronics,

Institute of Materials Research and System for

Sustainability, Nagoya University, Furo-cho, Chikusa-ku,

Aichi 464-8601, Japan

Graduate School of Engineering, Nagoya University, Furo-

cho, Chikusa-ku, Aichi 464-8603, Japan

Crystal IS, 70 Cohoes Avenue, Green Island, NY 12183,

United States of America

Applied Physics Express

https://doi.org/10.7567/1882-0786/ab50e0

We present a deep-ultraviolet semiconductor laser

diode that operates under current injection at room

temperature and at a very short wavelength. The

laser structure was grown on the (0001) face of a

single-crystal aluminum nitride substrate. The

measured lasing wavelength was 271.8 nm with a

pulsed duration of 50 ns and a repetition frequency

of 2 kHz. A polarization-induced doping cladding layer

was employed to achieve hole conductivity and

injection without intentional impurity doping. Even

with this undoped layer, we were still able to achieve

a low operation voltage of 13.8 V at a lasing threshold

current of 0.4 A.

Multiwavelength GaN‐Based Surface‐Emitting Lasers

and Their Design Principles Department of Electronic Engineering, East China Normal

University, 500 Dongchuan Road, Shanghai 200241, China

Shanghai Institute of Intelligent Electronics & Systems,

Fudan University, 220 Handan Road Shanghai 200433,

China

Annalen der physik

https://doi.org/10.1002/andp.201900308

Dual‐wavelength lasing operations are demonstrated

in GaN‐based vertical‐cavity surface‐emitting lasers

(VCSELs) comprising ingeniously designed asymmetric

InGaN quantum wells (AS‐QWs). The dual laser

modes show exact positive‐correlated polarization

dependences with a high degree of polarization of up

to 98%. By simply tuning the pump energy, the

components and intensity of the laser outputs can be

GaNEX | III-N Technology Newsletter No. 83 | 15

continuously changed, making wavelength selection

and switching available for the GaN‐based VCSELs.

Detailed theoretical analysis and experimental

measurements show that the intensity of optical gain

and the coupling between the active layer and optical

field, namely the electron–photon interaction, as well

as carrier tunneling and photon reabsorption play a

crucial role in the multiwavelength lasing processes.

Moreover, the design principles of the proposed

AS‐QWs and multistacked size‐varied quantum dot

(MS‐QD) active regions are elaborated to provide

guidelines for controllable multiwavelength

emissions in GaN‐based surface‐emitting lasers.

These results not only provide better understanding

of lasing in nitride‐based microcavity systems but also

shed insight into the more fundamental issues of

electron–photon coupling in such systems.

Importantly, such controllable multiwavelength laser

operations may extend nitride‐based VCSELs to

previously inaccessible areas, for example, flip‐flop,

ultrafast switches, and other functional devices such

as Raman lasers and sensors.

In-situ curvature measurements of AlInN/GaN

distributed Bragg reflectors during growths

containing substrate temperature ramping steps Department of Materials Science and Engineering, Meijo

University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya

468-8502, Japan

Graduate School of Engineering and Akasaki Research

Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya

464-8603, Japan

Journal of Crystal Growth

https://doi.org/10.1016/j.jcrysgro.2019.125357

We developed a model for in-situ wafer curvature

values of AlInN/GaN distributed Bragg reflectors

(DBRs) and determined InN mole fractions in the

DBRs with the model. In order to develop the model,

we experimentally investigated contributions of

substrate temperature ramping steps and a GaN

growth step to changes in the in-situ curvature during

the AlInN/GaN DBR growth. We found that an

increase of curvature change at the substrate

temperature ramping steps was explained by an

increase of the epitaxial layer thicknesses. Another

finding was that a strain in the GaN layer at the GaN

layer growth step was almost zero. Finally, we

determined the InN mole fractions in the AlInN layers

by using the model, showing excellent agreements

with the values estimated from ex-situ X-ray

diffraction measurements. The model reveals not

only the entire in-situ curvature change profile but

also the InN mole fraction under the precisely lattice-

matched condition of AlInN/GaN DBRs.

Effects of quantum well thickness and aluminum

content of electron blocking layer on InGaN-based

laser diodes Department of Applied Physics, China Agricultural

University, Beijing, China

State Key Laboratory of Integrated Optoelectronics,

Institute of Semiconductors, Chinese Academy of Science,

Beijing, China

School of Electronic, Electrical and Communication

Engineering, University of Chinese Academy of Sciences,

Beijing, China

Journal of Materials Science: Materials in Electronics

https://doi.org/10.1007/s10854-019-02539-8

The effects of quantum well (QW) thickness and

aluminum content of electron blocking layer (EBL) on

device performance of InGaN-based laser diodes

(LDs) are numerically investigated with LASTIP. It is

found that the device performance of the 3.0-nm-

thick QW LD is the best. The threshold current

increases and the output power at 120 mA decreases

when the QW thickness is too thin or too thick.

Actually, the optical and electrical characteristics of

InGaN-based LDs demonstrate that the optical

confinement factor decreases and optical loss

increases when the QW thickness is too thin. The

stimulated recombination rate decreases due to the

poorer overlap of electron–hole wave functions and

the enhanced polarization-induced built-in electric

field when the well thickness is too thick. Moreover,

the calculation results of LDs with different aluminum

compositions of EBL demonstrate that the

effectiveness of EBL would be enhanced through

increasing aluminum content when the thickness of

QWs decreases, because there is a reduction of

ground-state energy level and the energy difference

between the ground state and the top of the

quantum barrier.

GaNEX | III-N Technology Newsletter No. 83 | 16

Effect of Mg doping concentration of electron

blocking layer on the performance of GaN-based

laser diodes State Key Laboratory of Integrated Optoelectronics,

Institute of Semiconductors, Chinese Academy of Sciences,

Beijing, China

Center of Materials Science and Optoelectronics

Engineering, University of Chinese Academy of Sciences,

Beijing, China

Applied Physics B

https://doi.org/10.1007/s00340-019-7343-4

Performance of InGaN-based laser diodes (LDs) with

different Mg concentrations of electron blocking

layer (EBL) is investigated by simulation and

experimental methods. It is found from the

simulation results that the threshold current

decreases and slope efficiency increases, when the

Mg concentration of EBL increases from 2 × 1018 to

6 × 1019 cm−3; it is attributed to the suppression of

the leakage of electrons and the enhancement of the

injection of holes due to the variation of potential

barrier for them as the increase of Mg concentration

of EBL. These simulation results agree well with the

experimental ones, when the Mg concentration of

EBL is lower than 7.5 × 1018 cm−3. However, it

deteriorates when the Mg concentration increases to

1.2 × 1019 cm−3. It may be due to the increase of the

absorption loss of LDs.

Inhomogeneous Current Injection and Filamentary

Lasing of Semipolar (2021¯) Blue GaN‐Based

Vertical‐Cavity Surface‐Emitting Lasers with Buried

Tunnel Junctions Materials Department, University of California, Santa

Barbara, CA 93106, U.S.A

Department of Electrical and Computer Engineering,

University of California, Santa Barbara, CA 93106, U.S.A

physica status solidi a

https://doi.org/10.1002/pssa.201900718

Blue (202-1) semipolar vertical‐cavity

surface‐emitting lasers with a buried tunnel junction

current aperture are demonstrated under

continuous‐wave operation with a differential

efficiency of 4% and a threshold current of 2.7 mA for

a lasing mode at 452 nm. The effects of the aperture

diameter on these 9λ cavity length devices are

presented, showing that the differential efficiency

increases with aperture size, whereas the threshold

current density remains constant for apertures larger

than 10 μm. Filamentary lasing is observed in the

larger aperture sizes, and it is suggested that this

mode behavior is due to current injection

inhomogeneity across the aperture. This theory is

supported by the correlation between optical

nearfield images and thermal microscopy images.

Study on electronic blocking layer of 403 nm GaN-

based vertical cavity surface emitting lasers Key Laboratory of Opto-Electronics Technology, Ministry of

Education, Faculty of Information Technology, Beijing

University of Technology, Beijing, China

Optoelectronics Letters

https://doi.org/10.1007/s11801-019-9024-2

In order to obtain good optical characteristics in the

GaN-based vertical-cavity surface-emitting laser

(VCSEL), different kinds of AlGaN electron blocking

layers (EBL) were introduced. These were inserted

coherently near the active region to limit electron

leakage into the p-doped side. The research was

conducted by photonic integrated circuit simulator in

three-dimensional (PICS3D). The simulated results

reveal that an EBL can improve the optical

characteristics of a VCSEL effectively. All the

advantages are due to a reduction in the electron

leakage in the quantum wells. While the voltage of

the five-layer EBLs LD is lower than the voltage of the

seven-layer EBLs LD, the output power of the two is

approximately the same, so the five-layer EBLs is the

best choice for comprehensive structure analysis as

the epitaxial structure can be grown more easily on

it.

GaNEX | III-N Technology Newsletter No. 83 | 17

GROUP 3 - Power Electronics Group leader: Frédéric Morancho (LAAS-CNRS)

Information selected by Frédéric Morancho (LAAS-CNRS) and Yvon Cordier (CRHEA-CNRS)

Analysis of the Significant Rise in Breakdown Voltage of GaN HEMTs from Near-Threshold to Deep Off-state Gate Bias Conditions Indian Institute of Technology Madras, India

IEEE Transactions on Device and Materials Reliability

https://doi.org/10.1109/TDMR.2019.2950604

We investigate AlGaN/GaN high electron mobility

transistors with 0.7 μm gate length whose measured

off-state breakdown voltage, VBR, increased from 28

V at gate-source bias, VGS =-4.1 V (near threshold,

VT) to 87-138 V at VGS =-9.5 V (deep off-state); this

VBR rise was accompanied by a positive VT shift of

0.17-0.5 V; devices with larger VT shift showed larger

VBR rise. Our prior work showed that the near-

threshold VBR is due to space-charge limited current,

which is a signature of buffer traps. Our analysis of

the above observations of the present work shows

the following: The deep off-state VBR is due to

impact ionization induced avalanche. The correlation

between VT shift and VBR rise implies that barrier

and/or buffer traps play a role in governing VBR.

Although different models involving surface, barrier

and buffer traps can simulate the combination of

positive VT shift and large VBR rise, DC electric stress

most likely affects the surface and barrier traps but

not buffer traps.

H-terminated polycrystalline diamond p-channel

transistors on GaN-on-Silicon Ecole polytechnique federale de Lausanne, CH-1015

Lausanne, Switzerland

Lake Diamond SA, CH-1015 Lausanne, Switzerland

IEEE Electron Device Letters

https://doi.org/10.1109/LED.2019.2953245

In many semiconductor technologies, including GaN,

the lack of p-channel devices is a major obstacle for

complementary operations. Here, we demonstrate

highperformance polycrystalline diamond p-channel

transistors on GaN-on-Si. Following the optimization

of the microwave-plasma chemical-vapor-deposition

of diamond on GaN, the polycrystalline layer was

hydrogenated to form a 2D hole-gas at the surface,

acting as p-channel. Relying on a rather simple

fabrication process, these devices exhibited excellent

electrical and thermal performances with on-off ratio

of 109, breakdown voltage of 400 V, specific on-

resistance of 84 mΩ ·, and thermal conductivities

higher than 900 W/m·K. The presented hetero-

integration technology provides a promising platform

for future complementary logic operations, gate

drivers, complementary power switch applications

such as integrated power inverters and converters,

simultaneously serving as a very efficient thermal

management solution in high power density

applications.

Suppression of substrate coupling in GaN high

electron mobility transistors (HEMTs) by hole

injection from the p-GaN gate Engineering Department, University of Cambridge,

Cambridge, CB2 1PZ, United Kingdom

Infineon Technologies Americas Corp., El Segundo,

California 90245, USA

Infineon Technologies Austria AG, 9500 Villach, Austria

Applied Physics Letters

https://doi.org/10.1063/1.5121637

GaN-on-Si is a lateral technology and as such it allows

the integration of high voltage High Electron Mobility

Transistors and low voltage devices on the same chip,

thus enabling the miniaturization and reduction of

parasitic inductances. Due to the fact that integrated

devices share a common substrate, the performance

of one device can be significantly affected by the

operation of another. The choice of the substrate

bias is particularly important in the integrated half-

bridge, a popular topology which includes a low- and

a high-side device. A grounded substrate will cause

vertical stress on the high-side device, while a

floating substrate will couple with the high voltage,

resulting in stress on the low-side device. This is

highly problematic as the devices may fail to turn on

or have a significantly increased RON. In this work,

we carefully investigate the substrate coupling of a

GaNEX | III-N Technology Newsletter No. 83 | 18

high-side and low-side device via backgating

measurements. We demonstrate that the unwanted

RON increase in the high side device could be

suppressed by hole injection from the gate, if the

gate is formed of a p-type material.

Modeling of the Impact of the Substrate Voltage on

the Capacitances of GaN-on-Si HEMTs Fraunhofer Institute for Applied Solid State Physics, 79108

Freiburg im Breisgau, Germany

School of Engineering, Macquarie University, Sydney, NSW

2109, Australia

IEEE Transactions on Electron Devices

https://doi.org/10.1109/TED.2019.2948828

Measurement results of the terminal capacitances of

a high-voltage power GaN high-electron-mobility

transistor on a conductive-Si substrate are presented.

These results show significant dependence of these

capacitances on the substrate (or bulk/backside)

voltage. In this article, we enhance the ASM-GaN

compact model, which is a recently selected industry

standard model for GaN devices, to account for this

dependence. A detailed description of the modeling

procedure is presented. Simulation results based on

the enhanced model are in excellent agreement with

measurement results. The model enables the design

of advanced high-voltage GaN power ICs, such as

half-bridges with drivers and logic, on a conductive Si-

substrate, taking capacitive substrate coupling into

account during simulations.

Determination of electronic band structure by

electron holography of etched-and-regrown

interfaces in GaN p-i-n diodes Department of Physics, Arizona State University, Tempe,

Arizona 85287, USA

School of Electrical, Computer and Energy Engineering,

Arizona State University, Tempe, Arizona 85287, USA

Applied Physics Letters

https://doi.org/10.1063/1.5127014

The electrostatic potential variation across etched-

and-regrown GaN p-i-n diodes for power electronics

has been studied using electron holography in a

transmission electron microscope. The potential

profiles have been correlated with the composition

profiles of Mg, Si, and O obtained by secondary ion

mass spectroscopy. Electronic charges obtained from

the potential profiles correlate well with the presence

of Si and O impurities at regrown interfaces. The

overlap of Mg and Si when Mg doped GaN is grown

directly over an etched undoped GaN surface results

in the formation of a highly doped p-n junction. The

introduction of a thin undoped layer over the etched

GaN surface prevents the formation of such a

junction as the regrowth interface is moved away

from the Mg-doped GaN, and results in diodes with

improved reverse leakage currents, close to the best

values of continuously grown p-i-n diodes. Potential

profiles of continuously grown (not etched) p-i-n

diodes are compared to those of etched-and-regrown

diodes.

Ohmic contact to AlN:Si using graded AlGaN contact

layer NTT Basic Research Laboratories, NTT Corporation, Atsugi,

Kanagawa 243-0198, Japan

Applied Physics Letters

https://doi.org/10.1063/1.5124936

We formed a graded-AlGaN contact layer to improve

the Ohmic characteristics of Si-doped AlN. Linear I-V

characteristics were obtained for AlN with the

graded-AlGaN layer, and the current was three orders

of magnitude larger than that for AlN without the

one. The specific contact resistivity decreased with

the increasing thickness of the graded-AlGaN layer.

This was probably due to a reduction in the three-

dimensional negative charge density induced by the

polarization charge in the graded AlGaN layer. A

minimum contact resistivity of 1.4 ×10−2 Ω cm2 was

obtained for a 330-nm-thick graded-AlGaN layer. To

obtain the Ohmic contact, the Si-dopant

concentration (NSi) should be larger than the

negative fixed charge density (ρπ) induced by the

polarization charge. However, the heavily doped

graded-AlGaN layer (NSi=2.4×1019 cm−3) became

semi-insulating due to self-compensation. The results

indicated that reducing ρπ by relaxing the

compositional slope in the graded layer can improve

the Ohmic characteristics.

GaNEX | III-N Technology Newsletter No. 83 | 19

Ultra-low Contact Resistivity of < 0.1 Ω·mm for Au-

free TixAly Alloy Contact on Non-recessed i-

AlGaN/GaN State Key Laboratory of ASIC and System, School of

Microelectronics, Fudan University, Shanghai 200433,

China

School of Microelectronics, Southern University of Science

and Technology (SUSTech)

GaN Device Engineering Technology Research Center of

Guangdong, SUSTech

Laboratory of the Third Generation Semi-conductor,

SUSTech, 518055 Shenzhen, Guangdong, China

IEEE Electron Device Letters

https://doi.org/10.1109/LED.2019.2953077

A robust process for Au-free ohmic contact formation

is demonstrated by a direct contact of TixAly alloy

film on non-recessed i-AlGaN/GaN. Using this novel

TixAly alloy instead of multilayers as contact metals,

an ultra-low contact resistivity of < 0.1 Ω·mm is

achieved for Ti5Al1 alloy on i-AlGaN/GaN after

880°C/60s annealing.

Effect of the High-Temperature Off-State Stresses on

the Degradation of AlGaN/GaN HEMTs Key Laboratory for Wide Band Gap Semiconductor

Materials and Devices of Education, The School of

Microelectronics, Xidian University, Xi’an 710071, China

Electronics

https://doi.org/10.3390/electronics8111339

GaN-based high electron mobility transistors offer

high carrier density combined with high electron

mobility and often require operation at high

frequencies, voltages, and temperatures. The device

may be under high temperature and high voltage at

the same time in actual operation. In this work, the

impact of separate off-state stresses, separate high-

temperature stresses, and off-state stresses at high

temperatures on AlGaN/GaN high electron mobility

transistors (HEMTs) grown on Si substrates was

investigated. The output current and gate leakage of

the device degenerated to different degrees under

either isolated off-state or high-temperature stress.

The threshold voltage of the device only exhibited

obvious negative drift under the action of high-

temperature and off-state stresses. The parameter at

high temperature (or room temperature) before

stress application was the reference. We found that

there was no significant difference in the degradation

rate of drain current and transconductance peak

when the same off-state stress was applied to the

device at different temperatures. It was concluded

that, under the high-temperature off-state electric

field pressure, there were two degradation

mechanisms: one was the inverse piezoelectric

polarization mechanism only related to the electric

field, and the other was the degradation mechanism

of the simultaneous action of temperature and

electric field.

Cascode GaN/SiC: A Wide-Bandgap Heterogenous

Power Device for High-Frequency Applications Electrical Engineering, Stanford University, Stanford,

California United States 94305

Tsinghua University, 12442 Beijing, Beijing China 100084

Stanford University Department of Aeronautics and

Astronautics, 198869 Stanford, California United States

94305-4035

IEEE Transactions on Power Electronics

https://doi.org/10.1109/TPEL.2019.2954322

Wireless power transfer systems and plasma

generators are among the increasing number of

applications that use high-frequency power

converters. Increasing switching frequency can

reduce the energy storage requirements of the

passive elements that can lead to higher power

densities or even the elimination of magnetic cores.

However, operating at higher frequencies requires

faster switching devices in packages with low-

parasitics. Wide bandgap (WBG) power devices like

Gallium Nitride (GaN) and Silicon Carbide (SiC)

devices, have high critical fields and high thermal

conductivity that make them good candidates for

efficient high-voltage and high-frequency operations.

Commercially available GaN and SiC devices have

ratings targeting different applications. Lateral GaN

devices dominate in lower-voltage (<650 V) and high-

frequency applications as they have relatively small

device capacitances (Coss, Ciss), which make them

easy to drive at high frequencies. On the other hand,

vertical SiC devices are often used in higher-voltage

and lowfrequency applications since they have higher

blocking voltages and larger gate charge than their

GaN counterparts. As a result, SiC devices usually

GaNEX | III-N Technology Newsletter No. 83 | 20

require high-power and complicated gate drive

circuitry. Recent work shows that in both GaN and SiC

devices, losses in device Coss can exceed the

conduction losses at high switching frequencies and

relatively high voltages under Zero-Voltage-Switching

(ZVS) conditions. Moreover, the Coss energy loss

(Eoss) per switching cycle increases with frequency in

GaN devices but remains roughly independent of

frequency in SiC devices. This means that at high

frequencies, SiC devices can be preferable due to

their smaller Coss energy loss even when taking into

consideration the complexity of the gate drive circuit.

In this paper, we present a WBG high-voltage cascode

GaN/SiC power device, combining the advantages of

both a GaN and a SiC device - namely, simple gate

drive requirements, ${E_{oss}$ loss per cycle roughly

independent of frequency, and relatively high voltage

blocking capability. Comparing this cascode GaN/SiC

device with a SiC MOSFET and a SiC JFET of similar

voltage ratings and Rds,ON, we find that the inverter

using the cascode GaN/SiC device has the highest

efficiency and simplest auxiliary gate drive circuitry.

Finally, integrating the cascode GaN/SiC device has

the potential benefits of achieving lower Coss losses,

higher device ratings, and better heat removal

capability.

Band alignment of BeO gate dielectric grown by

atomic-layer deposition on AlGaN/GaN HEMTs School of Integrated Technology, Yonsei University,

Incheon 21983, Republic of Korea

Yonsei Institute of Convergence Technology, Incheon

21983, Republic of Korea

Center for Multidimensional Carbon Materials (CMCM),

Institute for Basic Science (IBS), Ulsan 44919, Republic of

Korea

Department of Chemistry, Ulsan National Institute of

Science and Technology (UNIST), Ulsan 44919, Republic of

Korea

Applied Surface Science

https://doi.org/10.1016/j.apsusc.2019.144107

In this study, we demonstrated the band alignment

between a BeO and AlGaN/GaN heterointerface. The

bandgap of the BeO film was measured to be 8.2 ±

0.05 eV by reflection electron energy loss

spectroscopy. A valence band offset of the

BeO/AlGaN interface was determined to be 1.1 ± 0.1

eV by X-ray photoelectron spectroscopy. Based on

the spectral analysis result, the conduction band

offset was calculated to be 3.2 ± 0.1 eV. When BeO

was used as the gate dielectric of an AlGaN/GaN

transistor, the on/off current ratio was improved to

107. The results of the band alignment and electrical

testing open up opportunities for the application of

BeO films to the gate dielectric of GaN-based high-

power devices.

High Voltage Vertical GaN p-n Diodes with

Hydrogen-Plasma based Guard Rings School of Electrical, Computer, and Energy Engineering,

Arizona State University, Tempe, AZ, 85287 USA

Department of Physics, Arizona State University, Tempe,

AZ, 85287 USA

IEEE Electron Device Letters

https://doi.org/10.1109/LED.2019.2954123

This letter demonstrates novel hydrogen-plasma

based guard rings (GRs) for high voltage vertical GaN

p-n diodes grown on bulk GaN substrates by

metalorganic chemical vapor deposition (MOCVD).

The GR structure can significantly improve

breakdown voltages (BV) and critical electric fields

(Ec) of the devices. Not having field plates or

passivation, the p-n diodes with a 9 µm drift layer

and 10 GRs showed BV/on-resistance (Ron) of 1.70

kV/0.65 mΩ·cm2, which are close to the GaN

theoretical limit. Moreover, the device also exhibited

good rectifying behaviors with an on-current of ∼ 2.6

kA/cm2, an on/off ratio of ∼ 10 10, and a turnon

voltage of 3.56 V. This work represents one of the

first effective GR techniques for high performance

kV-class GaN p-n diodes.

Lateral GaN JFET Devices on Large Area Engineered

Substrates U.S. Naval Research Laboratory, Washington, DC 20375,

USA

Qromis, Inc., Santa Clara, Calfornia 95051, USA

ECS J. Solid State Sci. Technol.

https://doi.org/10.1149/2.0091912jss

Lateral GaN-based p-n junction gated field effect

transistor (LJFET) power transistors on large area

substrates were fabricated as a proof-of-concept to

GaNEX | III-N Technology Newsletter No. 83 | 21

evaluate candidate power switching devices that

could be designed with avalanche breakdown

capability. The devices performed to design

specifications aimed at demonstrating a device

suitable for operation in cascode with a normally-off

low-voltage Si based transistor companion. The

maximum current density was 200 mA/mm and

threshold voltage was −30V. Large gate width devices

(40mm) exhibited >1A current. The devices have

blocking capability to 800V. Initial testing of the

switching dynamics indicates low dynamic RON even

with an un-optimized buffer.

Dynamic On-Resistance in GaN-on-Si HEMTs:

Origins, Dependencies, and Future Characterization

Frameworks Electrical Engineering, Stanford University, Stanford,

California United States 94305

ITET, ETH Zurich, Zurich Switzerland 8092

Electrical Engineering, ETH Zurich, Zurich Switzerland 8044

IEEE Transactions on Power Electronics

https://doi.org/10.1109/TPEL.2019.2955656

Gallium nitride high-electron-mobility transistors

(GaN HEMTs) exhibit dynamic on-resistance ( dRon ),

where the on-resistance immediately after turn-on is

higher than the DC value. A proliferation of recent

literature reports dRon , with some publishing an 8×

increase in conduction losses and others finding that

the problem is nonexistent. This variation can be

largely attributed to the standardized double-pulse-

test (DPT) method, which does not specify blocking

time and will ignore any effects that accumulate over

multiple switching cycles. Absent consistent

measurements, designers are left without an

accurate conduction loss estimate in converters with

GaN HEMTs. We discuss the underlying causes of

charge trapping to find the key influences over dRon ,

and show that the DPT technique gives invalid

results. Our measurements validate that each

operating parameter must be independently

controlled and that only steady-state dRon

measurements will predict dRon performance. For

the commercial GaN HEMT tested in this paper, the

worst-case dRon is nearly 2× higher than the DC

resistance at the same temperature, confirming that

accurate dRon characterization remains critical to

predicting converter characteristics. Finally, we

provide a reporting framework for GaN HEMT

manufacturers and methods to estimate conduction

losses in converters with GaN HEMTs.

High ION and ION/IOFF Ratio Enhancement-Mode

Buried p-Channel GaN MOSFETs on p-GaN Gate

Power HEMT Platform Department of Electronic and Computer Engineering, The

Hong Kong University of Science and Technology, Clear

Water Bay, Hong Kong

InnoScience Technology, Zhuhai, China

IEEE Electron Device Letters

https://doi.org/10.1109/LED.2019.2954035

Enhancement-mode (E-mode) buried p-channel GaN

metal-oxide-semiconductor field-effect-transistors (p-

GaNMOSFET’s) with threshold voltage (VTH) of -1.7 V,

maximum ON-state current (ION) of 6.1 mA/mm and

ION/IOFF ratio of 107 are demonstrated on a

standard p-GaN/AlGaN/GaN-on-Si power HEMT

substrate. An oxygen plasma treatment (OPT) was

deployed to the gated p-GaN region where a

relatively thick (i.e. 31 nm) GaN is retained without

aggressive gate recess. The OPT converts the top

portion of the GaN layer to be free of holes so that

only the bottom portion remains p-type while being

spatially separated from the etched GaN surface and

gate-oxide/GaN interface. As a result, E-mode

operation is enabled while a high-quality p-channel is

retained. Multi-energy fluorine ion implantation was

implemented for planar isolation of GaN p-channel

FETs with mesa edges and sidewalls eliminated.

Consequently, high ION/IOFF ratio is obtained.

Two-Step Mesa Structure GaN p-n Diodes with Low

On-resistance, High Breakdown Voltage and

Excellent Avalanche Capabilities

IEEE Electron Device Letters

https://doi.org/10.1109/LED.2019.2955720

Vertical structure GaN power devices fabricated on

freestanding GaN substrates have high potentials in

ideally efficient energy conversion systems. This

letter describes successful acquisition of high

avalanche capabilities for high breakdown voltage

GaN p-n junction diodes. We have already reported

the high avalanche capability by applying a punch-

GaNEX | III-N Technology Newsletter No. 83 | 22

through structure in p-GaN layer, however; the

structure caused a drawback of increase in on-

resistance and turn-on voltage. By applying a newly

developed two-step mesa structure consisting of the

first inner mesa with partially thinned p-GaN layer

and the second outer mesa etched to n-GaN drift

layer, the high avalanche capabilities with reversible

current-voltage characteristics have been realized at

high breakdown voltages of 4.7-4.8 kV without

sacrificing the forward I-V characteristics. The two-

step mesa structure transferred the position of the

peak electric field in the p-n junction from the dry-

etch damaged second outer mesa to the first mesa

covered by the thinned p-GaN layer, which could lead

the mild breakdown. The high avalanche capability

was obtained with good reproducibility regardless of

the anode electrode diameter. This structure can

contribute to the construction of robust power

systems.

Time-dependent characteristics and physical

mechanisms of AlGaN/GaN metal–insulator–

semiconductor high electron mobility transistors

under different bias conditions School of Materials Science and Engineering, The Key

Laboratory of Key Film Materials and Application for

Equipments (Hunan Province), Xiangtan University,

Xiangtan, Hunan 411105, People's Republic of China

Science and Technology on Reliability Physics and

Application of Electronic Component Laboratory, No.5

Electronics Research Institute of the Ministry of Industry

and Information Technology, Guangzhou 510610, People's

Republic of China

School of Electronics and Information Technology, Sun Yat-

sen University, Guangzhou 510275, People's Republic of

China

Journal of Physics D: Applied Physics

https://doi.org/10.1088/1361-6463/ab3d52

We experimentally investigate the time-dependent

degradation of AlGaN/GaN metal–insulator–

semiconductor high electron mobility transistors

subjected to different bias conditions. By means of

the combined performance under OFF/SEMI-ON/ON

state bias conditions, the dependence of threshold

voltage (V th), maximum transconductance (g m) and

saturation drain current (I dsat) on stress mode are

revealed. In the OFF-state, with the high temperature

reverse bias stress, the main mechanism is the

charge-trapping in the gate dielectric layer, leading to

the recoverable negative shift of the V th. In the

SEMI-ON-state, because of the hot-carrier injection,

the hot electrons could break the Si–H bonds,

resulting in the generation of interface states and can

also be captured by the trap states in the AlGaN

barrier or GaN buffer. This effect will cause the

decrease of saturation drain current and an

unrecoverable V th negative shift. In the ON-state,

due to the attenuation of hot electrons effect, V th

hardly changes, while I dsat has a dramatic decrease

caused by the self-heating effect. Low frequency

noise characteristics were used to extract the defect

state density, which then increases by about three

orders of magnitude after SEMI-ON-state stress.

Transmorphic epitaxial growth of AlN nucleation

layers on SiC substrates for high-breakdown thin

GaN transistors Thin Film Physics Division, Department of Physics (IFM),

Linköping University, SE-581 83 Linköping, Sweden

SweGaN AB, Teknikringen 8D, SE-583 30 Linköping,

Sweden

Institute of Electronic, Microelectronic and

Nanotechnology, Av. Poincaré, 59650 Villeneuve d'Ascq,

France

Applied Physics Letters

https://doi.org/10.1063/1.5123374

Interfaces containing misfit dislocations deteriorate

electronic properties of heteroepitaxial wide bandgap

III-nitride semiconductors grown on foreign

substrates, as a result of lattice and thermal

expansion mismatches and incompatible chemical

bonding. We report grain-boundary-free AlN

nucleation layers (NLs) grown by metalorganic

chemical vapor deposition on SiC (0001) substrates

mediated by an interface extending over two atomic

layers L1 and L2 with composition (Al1/3Si2/3)2/3N

and (Al2/3Si1/3)N, respectively. It is remarkable that

the interfaces have ordered vacancies on one-third of

the Al/Si position in L1, as shown here by analytical

scanning transmission electron microscopy and ab

initio calculations. This unique interface is coined the

out-of-plane compositional-gradient with in-plane

vacancy-ordering and can perfectly transform the in-

plane lattice atomic configuration from the SiC

GaNEX | III-N Technology Newsletter No. 83 | 23

substrate to the AlN NL within 1 nm thick transition.

This transmorphic epitaxial scheme enables a critical

breakdown field of ∼2 MV/cm achieved in thin GaN-

based transistor heterostructures grown on top.

Lateral breakdown voltages of 900 V and 1800 V are

demonstrated at contact distances of 5 and 20 μm,

respectively, and the vertical breakdown voltage is ≥3

kV. These results suggest that the transmorphic

epitaxially grown AlN layer on SiC may become the

next paradigm for GaN power electronics.

Solid-State Carbon-Doped GaN Schottky Diodes by

Controlling Dissociation of the Graphene Interlayer

with a Sputtered AlN Capping Layer Department of Materials Science and Engineering, National

Taiwan University of Science and Technology, Taipei 106,

Taiwan

Department of Materials Science and Engineering, Korea

University, Seoul 02841, Korea

Materials and Electro-Optics Research Division, National

Chung-Shan Institute of Science and Technology, Taoyuan

320, Taiwan

ACS Appl. Mater. Interfaces

https://doi.org/10.1021/acsami.9b18976

Carbon-doped GaN (GaN:C) Schottky diodes are

prepared by controlling the destruction status of

graphene interlayer (GI) on the substrate. The GI

without a sputtered AlN capping layer (CL) was

destroyed due to ammonia precursor etching

behavior in a high-temperature epitaxy. The

damaged GI, like nano-graphite as a solid-state

carbon doping source, incorporated the epitaxial

growth of GaN layer. The secondary ion mass

spectroscopy depth profile indicated that the carbon

content in GaN layer can be tuned further by

optimizing the sputtering temperature of AlN CL due

to the better capping ability of high crystalline quality

AlN CL on GI being achieved at higher temperature.

The edge-type threading dislocation density (TDD)

and carbon concentration of the GaN:C layer with an

embedded 550 °C-grown AlN CL on a GI substrate can

be significantly reduced to 2.28x10^9 cm^-2 and

~2.88x10^18 cm^-3, respectively. Thus, a Ni-based

Schottky diode with ideality factor of 1.5 and barrier

height of 0.72 eV was realized on GaN:C. The series

resistance increased from 28 k-ohm at 303 K to 113 k-

ohm at 473 K, while the positive temperature

coefficient (PTC) of series resistance was ascribed to

the carbon doping that induced the compensation

effect and lattice scattering effect. The decrease of

the donor concentration was confirmed by

temperature-dependent capacitance-voltage (C-V-T)

measurement. The PTC characteristic of GaN:C

Schottky diodes created by dissociating the GI as a

carbon doping source should allow for the future use

of high-voltage Schottky diodes in parallel, especially

in high temperature environments.

Enhancement‐Mode AlGaN/GaN Vertical Trench

Metal–Insulator–Semiconductor

High‐Electron‐Mobility Transistors with a High Drain

Current Fabricated Using the AlGaN Regrowth

Technique Graduate School of Engineering, University of Fukui, 3-9-1

Bunkyo, Fukui 910-8507, Japan

physica status solidi a

https://doi.org/10.1002/pssa.201900622

Herein, the first successful fabrication of

enhancement (E)‐mode AlGaN/GaN vertical trench

metal–insulator–semiconductor (MIS)

high‐electron‐mobility transistors (HEMTs) using

n+‐GaN/p‐GaN/n−‐GaN epistructures on

free‐standing n+ substrates is reported. A trench with

smooth semipolar planes (sidewalls) with angles of

45° and 135° from the c‐plane is formed by reactive

ion etching. Using metalorganic vapor‐phase epitaxy,

a uniform thickness of the AlGaN layer is regrown in

the trench. Devices fabricated without Mg activation

treatment for p‐GaN show depletion (D)‐mode

operation. The operation mode is changed from D to

E when Mg activation annealing temperature exceeds

700 °C. A high drain current (ID) ≥ 0.8 A mm−1 is

obtained in the devices with a relatively low Mg

concentration (≤1 × 1018 cm−3), whereas a threshold

voltage (VTH) as high as 22 V is obtained in the

devices with a high Mg concentration

(5 × 1018 cm−3). The poorly controlled VTH with

doped Mg concentration is discussed from the

viewpoint of dehydrogenation of the p‐GaN layer.

GaNEX | III-N Technology Newsletter No. 83 | 24

Study of E-Mode AlGaN/GaN MIS-HEMT with La-

silicate Gate Insulator for Power Applications Department of Electronics Engineering, National Chiao-

Tung University, Hsinchu, Taiwan, ROC

Department of Materials Science and Engineering, National

Chiao-Tung University, Hsinchu, Taiwan, ROC

Institute of Lighting and Energy Photonics, National Chiao-

Tung University, Tainan, Taiwan, ROC

International College of Semiconductor Technology,

National Chiao-Tung University, Hsinchu, Taiwan, ROC

Department of Physical Electronics, Tokyo Institute of

Technology, O-okayama, Meguro-ku, Japan

Journal of Electronic Materials

https://doi.org/10.1007/s11664-019-07790-7

An enhancement-mode (E-mode) AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistor (MIS-HEMT) with La2O3/SiO2 gate insulator is investigated for high power application. The La2O3/SiO2 composite oxide formed amorphous La-silicate after post deposition annealing. Good oxide film quality and excellent La-silicate/AlGaN interface properties were achieved as evidenced by the capacitance–voltage (C–V) curves and hysteresis effect of the La-silicate on AlGaN/GaN metal–oxide–semiconductor capacitors. As a result, the E-mode AlGaN/GaN MIS-HEMT with La-silicate gate insulator shows good threshold voltage (Vth) stability and demonstrated only slightly increase in the dynamic on-resistance (Ron) after high drain bias stress test. The device also exhibits high current density of 752 mA/mm, high maximum transconductance of 210 mS/mm, low subthreshold swing of 104 mV/decade, and ION/IOFF = 107 when tested at VDS = 10 V. Furthermore, low on-resistance of 7.6 Ω mm, high

breakdown voltage of 670 V, and excellent delay time of 4.2 ps were achieved, demonstrating the La-silicate MIS-HEMTs have the potential to be used for power electronic applications. Influence of Oxygen–Plasma Treatment on In-Situ

SiN/AlGaN/GaN MOSHEMT with PECVD SiO2 Gate

Insulator School of Electronic and Electrical Engineering, Hongik

University, Seoul 04066, Korea

Materials

https://doi.org/10.3390/ma12233968

The influence of oxygen–plasma treatment on in situ

SiN/AlGaN/GaN MOS high electron mobility

transistor with SiO2 gate insulator was investigated.

Oxygen–plasma treatment was performed on in situ

SiN, before SiO2 gate insulator was deposited by

plasma-enhanced chemical vapor deposition

(PECVD). DC I-V characteristics were not changed by

oxygen plasma treatment. However, pulsed I-V

characteristics were improved, showing less

dispersion compared to non-treated devices. During

short-term gate bias stress, the threshold voltage

shift was also smaller in a treated device than in an

untreated one. X-ray photoemission spectroscopy

also revealed that SiO2 on in situ SiN with oxygen–

plasma treatment has an O/Si ratio close to the

theoretical value. This suggests that the oxygen

plasma treatment-modified surface condition of the

SiN layer is favorable to SiO2 formation by PECVD.

GaNEX | III-N Technology Newsletter No. 83 | 25

GROUP 4 - Advanced Electronics and RF Group leader: Jean-Claude Dejaeger (IEMN)

Information selected by Jean-Claude Dejaeger (IEMN) and Yvon Cordier (CRHEA-CNRS)

Linearity Improvement with AlGaN Polarization-Graded Field Effect Transistors with Low Pressure Chemical Vapor Deposition Grown SiNx Passivation Department of Electrical and Computer Engineering, The

Ohio State University, Columbus, OH-43210, USA

Qorvo, Inc., Richardson, TX-75081, USA

IEEE Electron Device Letters

https://doi.org/10.1109/LED.2019.2951655

In this letter, we discuss the application of low

pressure chemical vapor deposition (LPCVD) grown

SiNx passivation-first process to improve the power

density and linearity performance of a metal oxide

chemical vapor deposition (MOCVD) grown AlGaN

channel polarization-graded field-effect transistor

(PolFET). Significantly improved dispersion behavior

was observed compared to plasma enhanced

chemical vapor deposition (PECVD) grown SiNx

passivation. The Current collapse at 30 V drain

quiescent condition for pulsed I-V was reduced to 8%

(LPCVD) from 25% (PECVD). 10 GHz load-pull

measurement showed a maximum output power

density of 3.4 W/mm with a peak power added

efficiency (PAE) of 40%. Twotone intermodulation

distortion measurement at 10 GHz for devices with

150..m width revealed an OIP3 of 39 dBm and an

excellent corresponding linearity figure of merit

OIP3/PDC of 13.3 dB. This is the best device level

OIP3/PDC reported to date at Xband for III-Nitride

microwave transistors.

High Performance and Highly Robust AlN/GaN

HEMTs for Millimeter-Wave Operation CNRS-IEMN, Institut d’Electronique, de Microélectronique

et de Nanotechnologie, Villeneuve-d’Ascq, France

IEEE Journal of the Electron Devices Society

https://doi.org/10.1109/JEDS.2019.2952314

We report on a 3 nm AlN/GaN HEMT technology for

millimeter-wave applications. Electrical

characteristics for a 110 nm gate length show a

maximum drain current density of 1.2 A/mm, an

excellent electron confinement with a low leakage

current below 10 μA /mm, a high breakdown voltage

and a F T /F max of 63/300 GHz at a drain voltage of

20V. Despite residual trapping effects, state of the art

large signal characteristics at 40 GHz and 94 GHz are

achieved. For instance, an outstanding power added

efficiency of 65% has been reached at V DS = 10V in

pulsed mode at 40 GHz. Also, an output power

density of 8.3 W/mm at V DS = 40V is obtained

associated to a power added efficiency of 50%. At 94

GHz, a record CW output power density for Ga-polar

GaN transistors has been reached with 4 W/mm.

Additionally, room temperature preliminary

robustness assessment at 40 GHz has been

performed at V DS = 20V. 24 hours RF monitoring

showed no degradation during and after the test.

Improving the transconductance flatness of

InAlN/GaN HEMT by modulating VT along the gate

width Key Laboratory of Wide Band-Gap Semiconductor

Materials and Devices, School of Microelectronics, Xidian

University, Xi'an 710071, People's Republic of China

School of Advanced Materials and Nanotechnology, Xidian

University, Xi'an 710071, People's Republic of China

School of Physics and Optoelectronic Engineering, Xidian

University, Xi'an 710071, People's Republic of China

Applied Physics Express

https://doi.org/10.7567/1882-0786/ab48bf

A modulated V T HEMT with improved g m flatness is

demonstrated for high linearity application. The

modulated V T HEMT was achieved by connecting

two elements with different V T values in parallel

along the gate width, realizing a flat resulting transfer

curve, and the two different V T elements were

fabricated by recessing part area of the barrier along

the gate width under the gate region. The proposed

HEMT shows a gate voltage swing as high as 5.4 V, a

high drain current of approximately 2 A mm−1, and

an f T/f max of 63/125 GHz with a much flatter profile

within the large gate voltage range.

GaNEX | III-N Technology Newsletter No. 83 | 26

X-Band High-Efficiency Continuous Class B Power

Amplifier GaN MMIC Assisted by Input Second-

Harmonic Tuning School of Aeronautics and Astronautics, Zhejiang

University, Hangzhou 310027, China

The Project Management Center, Equipment Development

Department, Beijing 100000, China

Electronics

https://doi.org/10.3390/electronics8111312

This paper presents a high-efficiency continuous class

B power amplifier MMIC (Monolithic Microwave

Integrated Circuit) from 8 GHz to 10.5 GHz, fabricated

with 0.25 μm GaN-on-SiC technology. The Pedro

load-line method was performed to calculate the

optimum load of the GaN field-effect transistor (FET)

for efficiency enhancement. Optimized by an output

second-harmonic tuned network, fundamental to

second-harmonic impedance, mapping was

established point-to-point within a broad frequency

band, which approached the classic continuous class

B mode with an expanded high-efficiency bandwidth.

Moreover, the contribution to the output capacitance

of the FET was introduced into the output second-

harmonic tuned network, which simplified the

structure of the output matching network. Assisted

by the second-harmonic source-pull technique, the

input second-harmonic tuned network was optimized

to improve the efficiency of the power amplifier over

the operation band. The measurement results

showed 51–59% PAE (Power Added Efficiency) and

19.8–21.2 dB power gain with a saturated power of

40.8–42.2 dBm from 8 GHz to 10.5 GHz. The size of

the chip was 3.2 × 2.4 mm2.

Degradation of Ka-Band GaN LNA Under High-Input

Power Stress: Experimental and Theoretical Insights Microsystem and Terahertz Research Center, Institute of

Electronic Engineering, China Academy of Engineering

Physics, Chengdu 610200, China

Department of Physics, School of Science, Wuhan

University of Technology, Wuhan 430070, China

IEEE Transactions on Electron Devices

https://doi.org/10.1109/TED.2019.2947311

A 23-30-GHz gallium nitride (GaN) low-noise amplifier

(LNA) with a noise figure (NF) of 0.87-1.51 dB is

presented in this article. This LNA was fabricated with

100-nm gate-length GaN-on-silicon (GaN/Si)

microwave monolithic integrated circuit (MMIC)

process. The linear gain is 14-17 dB within the band.

For investigating the robustness of this LNA, 1-W

continuous wave (CW) at 27 GHz was stressed on the

input port of the LNA. The gain decreased, and the NF

increased after stress. Experimental research and

first-principles calculations were carried out to

investigate the physical origin of the degradation. The

dehydrogenation of VGa-H3 complexes causes the

decrease of gain, and the creation of VAl-H4in the

AlN barrier is supposed to cause an increase of NF.

Tensile Strain and Fermi Level Alignment in

Thermally Grown TiO2 and Al2O3 Based AlGaN/GaN

MOS-HEMTs Department of Electrical Engineering, Indian Institute of

Technology Bombay, Mumbai 400076, India

Solid-State Electronics

https://doi.org/10.1016/j.sse.2019.107702

This work reports on the origin of performance

improvement for thermally grown TiO2 and Al2O3

based AlGaN/GaN metal-oxide-semiconductor high

electron mobility transistors (MOS-HEMTs). The

oxides have been used as gate dielectrics and

passivation layer. High resolution X-ray diffraction, X-

ray photoelectron spectroscopy, and transistor

characteristics are analysed to investigate the

improvements in the two dimensional electron gas

(2DEG) concentration. The HRXRD analysis reveals

that in-plane tensile stress of AlGaN layer is increased

by 23% (12%) for TiO2 (Al2O3) sample as compared

to that of an as-grown sample. The induced tensile

stress in the AlGaN barrier layer enhances the

piezoelectric polarization charges which effectively

improve the carrier confinement and mobility at the

interface. The improvement in the DC characteristics

is observed as a reduction in the gate leakage current

without deteriorating gate control and

transconductance. The output characteristics of TiO2

(Al2O3) based MOS-HEMTs have shown a 60% (40%)

increment in the maximum saturation drain current

and 50% (40%) increment in the transconductance as

compared to that of a control sample. The RF

characteristics also show similar order of

improvements.

GaNEX | III-N Technology Newsletter No. 83 | 27

High frequency guided mode resonances in mass-

loaded, thin film gallium nitride surface acoustic

wave devices Quantum Engineering Technology Labs and Department of

Electrical and Electronic Engineering, University of Bristol,

Woodland Road, Bristol BS8 1UB, United Kingdom

Center for Device Thermography and Reliability, H.H. Wills

Physics Laboratory, University of Bristol, Woodland Road,

Bristol BS8 1UB, United Kingdom

Applied Physics Letters

https://doi.org/10.1063/1.5123718

We demonstrate high-frequency (>3 GHz), high

quality factor radio frequency (RF) resonators in

unreleased thin film gallium nitride (GaN) on sapphire

and silicon carbide substrates by exploiting acoustic

guided mode (Lamb wave) resonances. The

associated energy trapping, due to mass loading from

gold electrodes, allows us to efficiently excite these

resonances from a 50 Ω input. The higher phase

velocity, combined with lower electrode damping,

enables high quality factors with moderate electrode

pitch and provides a viable route towards high-

frequency piezoelectric devices. The GaN platform,

with its ability to guide and localize high-frequency

sound on the surface of a chip with access to high-

performance active devices, will serve as a key

building block for monolithically integrated RF front-

ends.

Enhancement of Hot Spot Cooling by Capped

Diamond Layer Deposition for Multifinger

AlGaN/GaN HEMTs Department of Mechanical and Aerospace Engineering,

Rutgers University, Piscataway, NJ 08854 USA

Department of Electrical and Computer Engineering,

University of Nebraska, Lincoln, NE 68588 USA

IEEE Transactions on Electron Devices

https://doi.org/10.1109/TED.2019.2951190

The impact of a capped diamond layer for enhanced

cooling of multifinger AlGaN/GaN high-electron-

mobility transistors (HEMTs) has been investigated

under the steady-state operating condition. By

depositing a capped diamond thin film onto the

HEMTs, the temperature distribution around the hot

spots tends to be more uniform and the junction

temperature can be suppressed significantly. The

capped diamond serves as a highly effective heat

spreader, and its thermal spreading ability depends

on the structural design patterns and working

conditions. Some key parameters affecting the

thermal performance of the capped diamond have

been examined, including the heat dissipation power

density, gate pitch distance, embedding depth of the

heat source, thermal boundary resistance, substrate

material, as well as the cap thickness. For the 12-

finger model with 20-μm gate pitch distance and gate

power density of 6 W/mm, a 20-μm layer of capped

diamond could reduce the junction temperature by

12.1% for GaN-on-diamond HEMTs and by 25.3% for

GaN-on-SiC HEMTs. Even with a 1-μm capped

diamond layer, the reduction would be 7.6% and

9.9%, respectively. The temperature reduction for

GaN-on-Si is more significant.

DC and RF Characterization of AlGaN/AlN/GaN/AlN

DH‐HEMT on Sapphire Nano-Optical Engineering, Korea Polytechnic University

(KPU), Siheung, Gyeonggi 427-793, Republic of Korea

School of Electronic and Electrical Engineering, Hongik

University, Seoul 04066, Republic of Korea

Department of Electrical and Computer Engineering, and

Inter-university Semiconductor Research Center, Seoul

National University, Seoul 08826, Republic of Korea

WAVICE inc. 2/F, 46, Samsung 1-ro 5-gil, Hwaseong-si,

Gyeonggi-do, 18449, Republic of Korea

physica status solidi a

https://doi.org/10.1002/pssa.201900695

We introduce the AlGaN/AlN/GaN/AlN

double‐heterostructure high electron mobility

transistor (DH‐HEMT) on sapphire substrate, and

compare its direct current (DC) and radio frequency

(RF) characteristics to the conventional GaN‐based

single‐heterostructure HEMT (SH‐HEMT) on SiC

substrate. The devices having the two‐finger gate

were fabricated with gate width of 200 μm (2 × 100

μm) and gate length of 500 nm. The DC performance

of the DH‐HEMT showed a transconductance of 0.233

S/mm and a maximum drain current density of 0.93

A/mm, comparable to that of the SH‐HEMT. There

was less pronounced kink‐effect in the DC I‐V

characteristics, whereas, the off‐state subthreshold

current was approximately four orders of magnitude

higher than that of SH‐HEMT. A pulsed I‐V

GaNEX | III-N Technology Newsletter No. 83 | 28

measurement showed a greatly suppressed slump

ratio Z1 and Z2 of 1.6 and 4.3% for the DH‐HEMT. It

was shown that the performances of a small and a

large signal characteristics of the DH‐HEMT were

equivalent to the GaN SH‐HEMT: the current gain

cut‐off frequency (fT) and the maximum oscillation

frequency (fmax) were 20.1 and 47.6 GHz, and the

output power density and the power added efficiency

(PAE) at the peak PAE, at 20 V drain voltage and 3.5

GHz frequency were 3.83 W/mm and 57.2%,

respectively.

A 23‐31 GHz gallium nitride high‐robustness

low‐noise amplifier with 1.1‐dB noise figure and

28‐dBm saturation output power Microsystem and Terahertz Research Center, China

Academy ofEngineering Physics, Chengdu, China

Institute of Electronic Engineering, China Academy of

EngineeringPhysics, Mianyang, China

Microwave and Optical Technology Letters

https://doi.org/10.1002/mop.32130

A 23 to 31 GHz low‐noise amplifier (LNA) based on

0.1‐μm gallium nitride (GaN) on silicon (Si) microwave

monolithic integrated circuit process is presented in

this work. Three‐stage cascade topology was used in

the LNA design with chip area of 1.9 × 0.8 mm2. The

measured linear gain is 22 to 27 dB with low input

and output return loss. The noise figure (NF) was

measured with cold source methodology, which is

0.93 to 1.36 dB across the working frequency band.

The power characteristics were measured, which

indicate that this LNA has 1‐dB compression point

output power (P1dB) of 23 dBm and saturated output

power (Psat) of 28 dBm. The measured

output‐referred third‐order intercept point (OIP3)

was at 34 dBm level, which indicates the high

linearity of this LNA. To inspect the robustness,

30 dBm continuous wave input power was injected

into the working LNA for 5 minutes, no obvious

degradation was found after stress. Compared with

the traditional gallium arsenide (GaAs) and indium

phosphide (InP) LNA, GaN LNA reported in this work

has comparable NF but much higher robustness.

Moreover, this LNA has very high linearity, which

increases the immunity to jamming signal, enables

more complicated modulation mode and improves

data throughput. As we know, there is no GaN LNA

achieving such high P1dB and Psat with NF below 1.4

dB at this frequency band. This GaN LNA has a great

potential in the applications of electronic war,

anti‐electromagnetic interference and signal

detection.

Enhancement of Johnson figure of merit in III‐V

HEMT combined with discrete field plate and AlGaN

blocking layer Department of Electronics andCommunication

Engineering, KarunyaInstitute of Technology and

Sciences,Coimbatore, Tamilnadu, India

Department of Electronics andCommunication

Engineering, SNSCollege of Technology,

Coimbatore,Tamilnadu, India

Department of Electronics andCommunication, Malaviya

NationalInstitute of Technology, Jaipur, Rajasthan,India

International Journal of RF and Microwave Computer-

Aided Engineering

https://doi.org/10.1002/mmce.22040

The performance of AlGaN/GaN HEMT is enhanced

by using discrete field plate (DFP) and AlGaN blocking

layer. The AlGaN blocking layer provides an excellent

confinement of electrons toward the GaN channel,

resulting very low subthreshold drain current of 10−8

A/mm. It reveals very high off state breakdown

voltage (BV) of 342 V for 250 nm gate technology

HEMT. The breakdown voltage achieved for the

proposed HEMT is 23% higher when compared to the

breakdown voltage of conventional field plate HEMT

device. In addition, the DFP reduces the gate

capacitance (CG) from 12.04 × 10−13 to

10.48 × 10−13 F/mm. Furthermore, the drain current

and transconductance (gm) reported for the

proposed HEMT device are 0.82 A/mm and 314

mS/mm, respectively. Besides, the cut‐off frequency

(fT) exhibited for the proposed HEMT is 28 GHz.

Moreover, the proposed HEMT records the highest

Johnson figure of merit (JFOM) of 9.57 THz‐V for

250 nm gate technology without incorporating

T‐gate.

GaNEX | III-N Technology Newsletter No. 83 | 29

Impact of the in-situ SiN Thickness on Low-

Frequency Noise in MOVPE InAlGaN/GaN HEMTs Normandie Univ., UNICAEN, ENSICAEN, CNRS, GREYC,

14000 Caen, France. He is now with the DEI, University of

Padova, 35122 Padua, Italy

III-V Lab, Thales Research and Technology, 91767

Palaiseau, France

IEMN, 59650 Villeneuve d'Ascq, France

IEEE Transactions on Electron Devices

https://doi.org/10.1109/TED.2019.2945296

This article reports on sub-10-nm quaternary barrier

InAlGaN/GaN high electron mobility transistors

(HEMTs) grown by metal-organic-vapor-phase-

epitaxy (MOVPE) with an in situ SiN passivation layer

and an ultrashort gate length of 200 nm. Two batches

of HEMTs with two SiN thicknesses (tSiN) of 14 and

22 nm are studied. Low-frequency noise (LFN)

measurements of the drain current have been carried

out in the linear regime and showed that the in situ

SiN thickness has no impact on the noise

performance. SID/ID² in the linear regime

dependence over the gate overdrive shows that the

channel noise is located under the gate and that the

noise is not impacted by the thickness of the in situ

SiN layer.

Computer‐aided design methodology for linearity

enhancement of multiwatt GaN HEMT amplifiers

using multiple parallel devices Bradley Department of Electrical andComputer

Engineering, Virginia Tech,Arlington, Virginia

AMCOM Communications, Inc.,Gaithersburg, Maryland

University of Massachusetts, Amherst,Massachusetts

International Journal of RF and Microwave Computer-

Aided Engineering

https://doi.org/10.1002/mmce.22010

This article presents a design methodology for

linearizing GaN HEMT amplifiers based on splitting a

large FET into multiple parallel FETs with same total

gate periphery and by biasing them individually. By

varying the biases, the magnitude and the phase of

the IMD3 components at the output of FET changes.

A detailed simulation methodology using commercial

microwave CAD software is presented. Simulation

results show that by biasing one device in Class AB

and other(s) in deep Class AB mode, IMD3

components of parallel FETs can be made out of

phase to each other leading to cancellation and

improvement in linearity. Three prototype circuits

were simulated using (a) a single 5 mm FET

(1 × 5 mm), (b) two parallel 2.5 mm FETs (2 × 2.5 mm),

and (c) four parallel 1.25 mm FETs (4 × 1.25 mm), for

a total gate periphery of 5 mm, over the frequency

range of 0.8 to 1.0 GHz. IMD3 improvement up to

20 dBc was achieved with the 4 × 1.25 mm circuit

when the FET biases were optimized. Measurement

results show improvement in linearity up to 20 dBc

for 4 × 1.25 mm circuit. The proposed method

improves linearity without a substantial penalty on

the power consumption and is straightforward to

implement.

Sensitivity analysis for an electron transport system:

application to the case of wurtzite gallium nitride Mathematics, and Computer Science and Engineering,

University of North Texas, Denton, USA

Department of Mathematics, New Mexico Tech, Socorro,

USA

School of Engineering, The University of British Columbia,

Kelowna, Canada

Electrical, Computer, and Systems Engineering and Physics,

Applied Physics, and Astronomy, Rensselaer Polytechnic

Institute, Troy, USA

School of Computing and Scientific Computing and Imaging

Institute, University of Utah, Salt Lake City, USA

Journal of Computational Electronics

https://doi.org/10.1007/s10825-019-01424-1

Monte Carlo simulations, which are widely used for

predicting the transport properties of

semiconductors, use a large number of parameters,

such as the effective masses, the non-parabolic

constants, the deformation potential, the phonon

energies, and the elastic constants. Most of these

parameters are not very well known or have different

reported computed or measured values. In this

paper, we employ an uncertainty quantification

technique that allows us to determine the effect of

the uncertainty of parameter values on the transport

properties computed using the Monte Carlo

technique and establish the key parameters that

strongly affect the results in contrast to the

parameters whose wide variation has a small overall

impact.

GaNEX | III-N Technology Newsletter No. 83 | 30

Comparative Study of Variations in Gate Oxide

Material of a Novel Underlap DG MOS-HEMT for

Analog/RF and High Power Applications Electronics and Communication Engineering, Heritage

Institute of Technology, Kolkata, India

Silicon

https://doi.org/10.1007/s12633-019-00316-0

In this paper an Underlap Double Gate (U-DG)

Symmetric Heterojunction AlGaN/GaN Metal Oxide

Semiconductor High Electron Mobility Transistor

(MOS-HEMT) with gate oxide materials of different

dielectric constant has been studied using gate oxide

materials such as Hafnium dioxide (HfO2), Silicon

dioxide (SiO2) and a symmetric gate stack (GS) of

HfO2-SiO2. In this work, the analog performance of

the devices has been studied on the basis of

parameters like transconductance (gm),

transconductance generation factor (gm/ID) and

intrinsic gain (gmR0). This paper depicts the effect of

varying oxide materials on the analog and RF figure of

merits (FOMs) such as the gate to drain capacitance

(CGD), gate to source capacitance (CGS) and total

gate capacitance (CGG), intrinsic resistances, cut-off

frequency (fT) and maximum frequency of oscillation

(fMAX) using non-quasi-static approach. Studies show

that the introduction of a gate oxide layer in the

MOS-HEMT device increases the gate controllability

reducing gate leakage currents improving RF

performance. U-DG AlGaN/GaN MOS-HEMT with

HfO2 gate dielectric shows superior Power output

efficiency (POE) of 55% compared to the HfO2-SiO2

composite structure and SiO2 with 26% and 20%

respectively.

A Study on the First‐Derivative Output Properties of

GaN Static Induction Transistor with Submicrometer

Fin Width Department of Electrical Engineering, Stanford University,

Stanford, CA 94305, USA

Department of Electrical and Computer Engineering,

University of California, Davis, CA 95616, USA

physica status solidi b

https://doi.org/10.1002/pssb.201900545

The first derivative of output curves of a

Schottky‐junction vertical channel GaN static

induction transistor (SIT) with a submicrometer‐sized

fin is studied to understand its fundamental electrical

properties. It is found that the derivative of output

curves increases with the increase in drain voltage

(Vds) in ohmic region because of the raised potential

minima in the channel, which is not seen in SITs with

a relatively long fin width. The influence of the gate

voltages (Vgs) and Vds on electric potential in the

channel is demonstrated by evaluating the

contribution of Vgs and Vds, expressed through two

coefficients α and β. The ratio of α to β increases up

to 31.1 from 16.3 with decrease in the fin width from

0.9 to 0.5 μm, showing a higher dependency of the

potential minima on Vgs and the fin width. The

voltage gain expressed by α/β is 14.9 dB for the GaN

SIT with a fin width of 0.5 μm.

GaNEX | III-N Technology Newsletter No. 83 | 31

GROUP 5 – MEMS and Sensors Group leader: Marc Faucher (IEMN) Information selected by Knowmade

Fabrication of AlN/GaN MSM photodetector with

platinum as schottky contacts Department of Applied Sciences Universiti Teknologi

MARA, Cawangan Pulau Pinang 13500 Permatang Pauh,

Penang, Malaysia

Universiti Kuala Lumpur, Malaysian Institute of Industrial

Technology (MITEC), Persiaran Sinaran Ilmu, Bandar Seri

Alam, 81750 Johor, Malaysia

Institute of Nano-Optoelectronics Research and

Technology Universiti Sains Malaysia, 11800 Penang,

Malaysia

Materials Research Express

https://doi.org/10.1088/2053-1591/ab4a40

The epitaxial aluminium nitride (AlN) layer was

fabricated on a silicon (111) substrate by solid phase

radio frequency (RF) MBE The samples morphological

characteristic was successfully studied by field

emission SEM. Low photo-response of the hetero-

structure layers is one of the main obstacles in order

to fabricate a high performance of photodetector

device. The platinum contacts on AlN/GaN metal-

semiconductor-metal (MSM) photodetector were

formed by RF sputtering machine. The conductivity

behaviours, Schottky barrier height (SBH), photo-

responses of the device were examined by source

meter measurement. The SBH values of photo-device

sensing were calculated as 0.488 eV and 0.479 eV for

dark current and photo current, respectively. Good

response times of the device were recorded as 21.48

ms and 12.69 ms for the bias voltage of 1 volt.

Static and dynamic simulation studies on the

AlGaN/GaN pressure sensor School of Information Science and Engineering, Chengdu

University, Chengdu 610106, People's Republic of China

School of Mechanical Engineering, Southwest Jiaotong

University, Chengdu 610031, People's Republic of China

Semiconductor Science and Technology

https://doi.org/10.1088/1361-6641/ab478a

In this paper, electro-thermo-mechanical coupled

static and dynamic FEM simulations are adopted to

study the AlGaN/GaN pressure sensor. The sensor

sensitivity is expressed as the drain current change of

transistor integrated on the AlGaN/GaN cantilever or

circular diaphragm with the applied pressure, namely

piezoresistive effect, which is caused essentially by

the change of piezoelectric polarization charge. In the

static simulation study, how the transistor self-

heating, gate metal layer, AlGaN donor-like surface

states, and bulk acceptor-like traps in GaN influence

the sensitivity are separately illustrated. In the

dynamic simulation study, transient behavior of the

sensor with the bulk acceptor-like traps and

dependences of the natural frequency of circular

diaphragm on the self-heating as well as the position

of transistor integrated on the diaphragm are

analyzed. This work would provide useful guidelines

for the design and optimization of AlGaN/GaN

pressure sensor.

On-diaphragm Thermistor for High-temperature

Dynamic Pressure Sensors University of Texas at Austin, Austin, TX 78758 USA

Silicon Audio, Inc., Austin, TX 78702 USA

IEEE Sensors Journal

https://doi.org/10.1109/JSEN.2019.2953397

This article presents the fabrication and

characterization of on-diaphragm Pt thermistors for

temperaturecompensated calibration of piezoelectric

pressure sensors. The micromachined pressure-

sensitive diaphragms are 700 µm in diameter and

employ AlN as the piezoelectric material. The

thermistors reside on top of the diaphragms and are

patterned into a 100-nm-thick sputtered Pt electrode

layer. Experimental characterization up to 600 °C

demonstrates the importance of annealing to realize

hysteresis-free resistance vs. temperature

characteristics. Dynamic frequency response

measurements of the pressure-sensitive diaphragms

vs. temperature demonstrate a marked shift in

compliance with temperature, and therefore

demonstrates the importance of temperature-

GaNEX | III-N Technology Newsletter No. 83 | 32

compensated pressure calibration in high-

temperature measurement environments.

TCAD model for TeraFET detectors operating in a

large dynamic range Electrical, Computer and Systems Engineering, Rensselaer

Polytechnic Institute, 8024 Troy, New York United States

IEEE Transactions on Terahertz Science and Technology

https://doi.org/10.1109/TTHZ.2019.2952248

Technology computer-aided design (TCAD) models

for AlGaAs/InGaAs and AlGaN/GaN and silicon SOI

TeraFETs are in good agreement with the measured

current-voltage characteristics and the response to

the sub-THz radiation. They allowed us to establish

the physical mechanism of the observed response

saturation at high intensities, not reproduced by the

analytical model. By activating or deactivating

different physical mechanisms in the TCAD models,

we show that the response saturation is caused by

the gate leakage for AlGaAs/InGaAs HFETs and

AlGaN/GaN HFETs and by the avalanche effect for Si

SOI MOSFETs.

Converse Magnetoelectric Composite Resonator for

Sensing Small Magnetic Fields Institute for Materials Science, Kiel University, Kiel, 24143,

Germany

Institute of Electrical and Information Engineering, Kiel

University, Kiel, 24143, Germany

MIREA - Russian Technological University, Moscow,

119454, Russia

IFW Dresden, SAWLab Saxony, Dresden, 01171, Germany

Scientific Reports

https://doi.org/10.1038/s41598-019-52657-w

Magnetoelectric (ME) thin film composites consisting

of sputtered piezoelectric (PE) and magnetostrictive

(MS) layers enable for measurements of magnetic

fields passively, i.e. an AC magnetic field directly

generates an ME voltage by mechanical coupling of

the MS deformation to the PE phase. In order to

achieve high field sensitivities a magnetic bias field is

necessary to operate at the maximum piezomagnetic

coefficient of the MS phase, harnessing mechanical

resonances further enhances this direct ME effect

size. Despite being able to detect very small AC field

amplitudes, exploiting mechanical resonances

directly, implies a limitation to available signal

bandwidth along with the inherent inability to detect

DC or very low frequency magnetic fields. The

presented work demonstrates converse ME

modulation of thin film Si cantilever composites of

mesoscopic dimensions

(25 mm × 2.45 mm × 0.35 mm), employing

piezoelectric AlN and magnetostrictive FeCoSiB films

of 2 µm thickness each. A high frequency mechanical

resonance at about 515 kHz leads to strong induced

voltages in a surrounding pickup coil with matched

self-resonance, leading to field sensitivities up to

64 kV/T. A DC limit of detection of 210 pT/Hz1/2 as

well as about 70 pT/Hz1/2 at 10 Hz, without the need

for a magnetic bias field, pave the way towards

biomagnetic applications.

Study of a GaN Schottky diode-based hydrogen

sensor with a hydrogen peroxide oxidation

approach and platinum catalytic metal Department of Chemical Engineering, National Cheng Kung

University, Tainan, 70101, Taiwan, Republic of China

Institute of Microelectronics, Department of Electrical

Engineering, National Cheng Kung University, Tainan,

70101, Taiwan, Republic of China

Department of Computer Science and Information

Engineering, Chaoyang University of Technology, Taichung,

41349, Taiwan, Republic of China

International Journal of Hydrogen Energy

https://doi.org/10.1016/j.ijhydene.2019.10.112

A platinum (Pt) catalytic metal and a hydrogen

peroxide oxidation approach are utilized to fabricate

a hydrogen sensor based on a GaN Schottky diode.

The presence of a gallium oxide dielectric layer

between the Pt metal and the GaN surface can

increase the adsorption sites for dissociated

hydrogen species, thereby improving the related

sensing ability towards hydrogen gas. Experimentally,

under introduced 1% hydrogen/air gas, the studied

device shows a high sensing response ratio of 1.03 ×

105 at 300 K. In addition, the lowest detecting level

of 1 ppm hydrogen at 300 K is obtained. This device

also exhibits good high-temperature durability (≥573

K) and a high sensing speed. The response (recovery)

time constant at 300 K is only 74 (103) sec even

under a very low hydrogen concentration of 1 ppm;

these time constant values are much smaller than

GaNEX | III-N Technology Newsletter No. 83 | 33

those of palladium metal-based sensors. Under the

1% hydrogen/air, the response (recovery) time

constant at 300 K is drastically reduced to 15 (19) sec.

Furthermore, in order to improve the feasibility of

transmitting the sensing data, the concept of linear

differentiation method is employed to eliminate

redundant data. The simulation result shows that the

average of the reduced ratios can achieve 77.88%.

Therefore, this Schottky diode device not only shows

promise to detect hydrogen gas, but also can be

utilized effectively in the transmission of sensing

data.

Seeing pressure in color based on integration of

highly sensitive pressure sensor and emission

tunable light emitting diode Graduate Institute of Applied Physics, National Taiwan

University, Taipei 10617, Taiwan

Department of Physics, National Taiwan University, Taipei

10617, Taiwan

Department of Electro-physics, National Chiao Tung

University, Hsinchu 30010, Taiwan

Department of Materials Science and Engineering, National

Tsing Hua University, Hsinchu 30013, Taiwan

Department of Photonics and Institute of Electro-optical

Engineering, National Chiao Tung University, Hsinchu

30010, Taiwan

Department of Chemical Engineering and Biotechnology,

National Taipei University of Technology, Taipei 10617,

Taiwan

Department of Physics, National Sun Yat-sen University,

Kaohsiung 80424, Taiwan

Optics Express

https://doi.org/10.1364/OE.27.035448

We demonstrate a highly sensitive, low-cost,

environmental-friendly pressure sensor derived from

a wool-based pressure sensor with wide pressure

sensing range using wool bricks embedded with a Ag

nano-wires. The easy fabrication and light weight

allow portable and wearable device applications. Wth

the integration of a light-emitting diode possessing

multi-wavelength emission, we illustrate a hybrid

multi-functional LED-integrated pressure sensor that

is able to convert different applied pressures to light

emission with different wavelengths. Due to the high

sensitivity of the pressure sensor, the demonstration

of acoustic signal detection has also been presented

using sound of a metronome and a speaker playing a

song. This multi-functional pressure sensor can be

implemented to technologies such as smart lighting,

health care, visible light communication (VLC), and

other internet of things (IoT) applications.

Fabrication and characterization of AlN-based

flexible piezoelectric pressure sensor integrated into

an implantable artificial pancreas CNR-IMM Institute for Microelectronics and Microsystems,

Via Monteroni, 73100, Lecce, Italy

BioRobotics Institute and Department of Excellence in

Robotics & AI, Scuola Superiore Sant’Anna, 56025,

Pontedera, Italy

Scientific Reports

https://doi.org/10.1038/s41598-019-53713-1

This study reports on the fabrication and

characterization of an event detection subsystem

composed of a flexible piezoelectric pressure sensor

and the electronic interface to be integrated into an

implantable artificial pancreas (IAP) for diabetic

patients. The developed sensor is made of an AlN

layer, sandwiched between two Ti electrodes,

sputtered on Kapton substrate, with a preferential

orientation along c-axis which guarantees the best

piezoelectric response. The IAP is made of an

intestinal wall-interfaced refilling module, able to

dock an ingestible insulin capsule. A linearly actuated

needle punches the duodenum tissue and then the

PDMS capsule to transfer the insulin to an implanted

reservoir. The device is located at the connection of

the needle with the linear actuator to reliably detect

the occurred punching of the insulin-filled capsule.

Finite Element Analysis (FEA) simulations were

performed to evaluate the piezoelectric charge

generated for increasing loads in the range of

interest, applied on both the sensor full-area and

footprint area of the Hamilton needle used for the

capsule punching. The sensor-interface circuit was

simulated to estimate the output voltage that can be

obtained in real operating conditions. The

characterization results confirmed a high device

sensitivity during the punching, in the low forces (0–

4 N) and low actuator speed (2–3 mm/s) ranges of

interest, meeting the requirement of the research

objective. The choice of a piezoelectric pressure

sensor is particularly strategic in the medical field due

to the request of self-powered implantable devices

GaNEX | III-N Technology Newsletter No. 83 | 34

which do not need any external power source to

output a signal and harvest energy from natural

sources around the patient.

Neutron detection performance of gallium nitride-

based semiconductors Department of Electrical and Computer Engineering,

Missouri University of Science and Technology, Missouri,

65409, USA

Department of Electrical and Computer Engineering,

University of North Carolina at Charlotte, Charlotte, North

Carolina, 28223, USA

Nuclear Engineering Program, Idaho State University,

Pocatello, Idaho, 83209, USA

Nuclear Engineering Program, Georgia Institute of

Technology, Atlanta, Georgia, 30332, USA

Southern Polytechnic College of Engineering and

Engineering Technology, Kennesaw State University,

Marietta, GA, 30060, USA

Scientific Reports

https://doi.org/10.1038/s41598-019-53664-7

Neutron detection is crucial for particle physics

experiments, nuclear power, space and international

security. Solid state neutron detectors are of great

interest due to their superior mechanical robustness,

smaller size and lower voltage operation compared to

gas detectors. Gallium nitride (GaN), a mature wide

bandgap optoelectronic and electronic

semiconductor, is attracting research interest for

neutron detection due to its radiation hardness and

thermal stability. This work investigated thermal

neutron scintillation detectors composed of GaN thin

films with and without conversion layers or rare-

earth doping. Intrinsic GaN-based neutron

scintillators are demonstrated via the intrinsic 14N(n,

p) reaction, which has a small thermal neutron cross-

section at low neutron energies, but is comparable to

other reactions at high neutron energies (>1 MeV).

Gamma discrimination is shown to be possible with

pulse-height in intrinsic GaN-based scintillation

detectors. Additionally, GaN-based scintillation

detector with a 6LiF neutron conversion layer and

Gd-doped GaN detector are compared with intrinsic

GaN detectors. These results indicate GaN scintillator

is a suitable candidate neutron detector in high-flux

applications.

Suspended tungsten trioxide (WO3) gate

AlGaN/GaN heterostructure deep ultraviolet

detectors with integrated micro-heater Department of Microelectronics, Delft University of

Technology, 2628 CD Delft, Netherlands

Research and Development Center for Solid State Lighting,

Institute of Semiconductors, Chinese Academy of Sciences,

Qinghua East Road 35A, 100083, Beijing, China

State Key Laboratory of Solid State Lighting, Beijing,

100083, China

Institute of Microelectronic, Tsinghua University 100084,

Beijing, China

Optics Express

https://doi.org/10.1364/OE.27.036405

A suspended WO3-gate AlGaN/GaN heterostructure

photodetector integrated with a micro-heater is

micro-fabricated and characterized for ultraviolet

photo detection. The transient optical characteristics

of the photodetector at different temperatures are

studied. The 2DEG-based photodetector shows a

recovery (170 s) time under 240 nm illumination at

150 ℃. The measured spectral response of WO3-gate

AlGaN/GaN heterostructure shows a high response in

deep ultraviolet range. Responsivity at 240 nm

wavelength is 4600 A/W at 0.5 V bias. These

characteristics support the feasibility of a high

accuracy deep UV detector based on the suspended

AlGaN/GaN heterostructure integrated with a micro-

heater.

Ultrafast pyroelectric photodetection with on-chip

spectral filters Department of Electrical and Computer Engineering, Duke

University, Durham, NC, USA

Sensors Directorate, Air Force Research Laboratory,

Wright–Patterson Air Force Base, Dayton, OH, USA

Ginzton Laboratory, Department of Electrical Engineering,

Stanford University, Stanford, CA, USA

Department of Physics, Duke University, Durham, NC, USA

Nature Materials

https://doi.org/10.1038/s41563-019-0538-6

Thermal detectors, such as bolometric, pyroelectric

and thermoelectric devices, are uniquely capable of

sensing incident radiation for any electromagnetic

frequency; however, the response times of practical

devices are typically on the millisecond

GaNEX | III-N Technology Newsletter No. 83 | 35

scale1,2,3,4,5,6,7. By integrating a plasmonic

metasurface with an aluminium nitride pyroelectric

thin film, we demonstrate spectrally selective, room-

temperature pyroelectric detectors from 660–

2,000 nm with an instrument-limited 1.7 ns full width

at half maximum and 700 ps rise time. Heat

generated from light absorption diffuses through the

subwavelength absorber into the pyroelectric film

producing responsivities up to 0.18 V W−1 due to the

temperature-dependent spontaneous polarization of

the pyroelectric films. Moreover, finite-element

simulations reveal the possibility of reaching a 25 ps

full width at half maximum and 6 ps rise time rivalling

that of semiconductor photodiodes8. This design

approach has the potential to realize large-area,

inexpensive gigahertz pyroelectric detectors for

wavelength-specific detection from the ultraviolet to

short-wave infrared or beyond for, for example, high-

speed hyperspectral imaging.

Low Voltage High-Energy α-Particle Detectors by

GaN-on-GaN Schottky Diodes with Record-High

Charge Collection Efficiency School of Electrical and Electronics Engineering, Nanyang

Technological University, Singapore 639798, Singapore

Temasek Laboratories @ NTU, Research Techno Plaza, 50

Nanyang Drive, Singapore 639798, Singapore

Center for Integrated Research of Future Electronics

(CIRFE), IMaSS, Nagoya University, Nagoya 464-8603,

Japan

National Isotope Center, GNS Science, Lower Hutt 5010,

New Zealand

Sensors

https://doi.org/10.3390/s19235107

A low voltage (−20 V) operating high-energy (5.48

MeV) α-particle detector with a high charge

collection efficiency (CCE) of approximately 65% was

observed from the compensated (7.7 × 1014 /cm3)

metalorganic vapor phase epitaxy (MOVPE) grown 15

µm thick drift layer gallium nitride (GaN) Schottky

diodes on free-standing n+-GaN substrate. The

observed CCE was 30% higher than the bulk GaN (400

µm)-based Schottky barrier diodes (SBD) at −20 V.

This is the first report of α–particle detection at 5.48

MeV with a high CCE at −20 V operation. In addition,

the detectors also exhibited a three-times smaller

variation in CCE (0.12 %/V) with a change in bias

conditions from −120 V to −20 V. The dramatic

reduction in CCE variation with voltage and improved

CCE was a result of the reduced charge carrier density

(CCD) due to the compensation by Mg in the grown

drift layer (DL), which resulted in the increased

depletion width (DW) of the fabricated GaN SBDs.

The SBDs also reached a CCE of approximately 96.7%

at −300 V.

GaNEX | III-N Technology Newsletter No. 83 | 36

GROUP 6 - Photovoltaics and Energy harvesting Group leader: Eva Monroy (INAC-CEA)

Information selected by Knowmade

Improved ability of artificial photosynthesis by using

InGaN/AlGaN/GaN electrode Key Lab. for New Type of Functional Materials in Hebei

Province, School of Materials Science and Engineering,

Hebei University of Technology, Tianjin 300132, People's

Republic of China

School of Electronic Engineering, Tianjin University of

Technology and Education, Tianjin 300222, People's

Republic of China

Applied Physics Express

https://doi.org/10.7567/1882-0786/ab495c

We have successfully demonstrated the enhanced

capability of CO2 conversion using InGaN/AlGaN/GaN

photoelectrode. The CO2 conversion ability of the

system is improved due to the improvement of the

cathode potential by changing the light absorbing

layer which effectively combines the piezoelectric

polarization effect of the AlGaN/GaN structure and

the high absorption for light by InGaN. Our results

suggest that the photocurrent is increased by two

times than that produced by AlGaN/GaN.

Furthermore, the ability of convert to CO is

enhanced. Aside from H2 and CO, the concentration

of hydrocarbons is also improved.

A new lattice-matched In0.17Al0.83N ~ GaN based

heterostructure IMPATT diode for terahertz

application State Key Discipline Laboratory of Wide Bandgap

Semiconductor Technology, School of Microelectronics,

Xidian University, Xi'an 710071, People's Republic of China

Weifang University, Weifang 261061, People's Republic of

China

Semiconductor Science and Technology

https://doi.org/10.1088/1361-6641/ab4786

Simulation studies are made on the dc and

microwave performance of a novel lattice-matched

In0.17Al0.83N/GaN heterostructure impact

avalanche transit time (IMPATT) diode designed at

the low-end terahertz frequency of 220 GHz. The

electric field, breakdown voltage, rf output power

and the dc-to-rf conversion efficiency of the

heterostructure IMPATT diodes are compared with

the GaN homostructure IMPATT diode. The results

show that, a more localized avalanche region width is

obtained for the heterostructure IMPATT diodes.

With value of 45 nm of the In0.17Al0.83N layer

width, the heterostructure IMPATT diode gives the

highest efficiency (15.4%) with moderate rf output

power density (1.62 MW cm−2), and the lowest Q-

factor (6.57) as compared to other heterostructure

and homostructure IMPATT diodes.

Development of InxGa1-xN/GaN Axial Multiple

Quantum Well Nanowire for Solar Cell Applications Faculty of Technology University of Blida.1, 09000, Blida,

Algeria

Institut d’Electronique, de Microe´lectronique et de

Nanotechnologie (IEMN), UMR CNRS 8520, Universite´ des

Sciences et Technologies de Lille 1, Avenue Poincare´, BP

60069, 59652, Villeneuve d’Ascq, France

Optik

https://doi.org/10.1016/j.ijleo.2019.163844

In this paper, we report a simulation and

investigation of a single InxGa1-xN/GaN axial multiple

quantum well nanowire (MQWNW) solar cell of

radius r = 190 nm and a length of L = 1165 nm. Our

results have been shown that 15 In0.15Ga0.85N

(QW) /GaN (barrier) periods is the maximum number

that our structure can be supported with an optimal

efficiency of about 1.65% achieved with ε = 1.5%. The

insertion of MQWs in nanowire permits the growth of

InxGa1-xN MQWs with high indium concentration of

about 50% and ε = 5%. At this indium concentration,

the optimal efficiency obtained was 1.70%.

Moreover; the structure has been studied with

respect to the nanowire radius. In this context, we

have shown that the efficiency enhancement

achieved through the increase of radius is attributed

to the increase of photo-carriers. Study of

polarization and proton irradiations has indicated the

negative effect of polarization on structure

GaNEX | III-N Technology Newsletter No. 83 | 37

performances and high resistance of III-N

semiconductor materials against the radiations,

respectively. From these novel structures we can

improve solar cell performance for new applications.

Boosting photoelectrochemical performance of GaN

nanowall network photoanode with

bacteriorhodopsin Central Scientific Instruments Organization, Sector-30C,

Chandigarh, 160030, India

AcSIR, Council of Scientific and Industrial Research,

Ghaziabad, 201002, India

School of Materials Science, Indian Association for the

Cultivation of Science, Kolkata, 700032, India

Institute of Microbial Technology, Sector 39A, Chandigarh,

160036, India

Jawaharlal Nehru Centre for Advanced Scientific Research,

Bangalore, 560064, India

International Journal of Hydrogen Energy

https://doi.org/10.1016/j.ijhydene.2019.10.184

The ever-increasing demand for renewable and clean

energy sources has prompted the development of

novel materials for photoelectrochemical (PEC) water

splitting, but efficient solar to hydrogen conversion

remains a big challenge. In this work, we report a bio-

nanohybrid strategy in a photo-system to

simultaneously enhance the charge separation and

water splitting efficiency of photoanode (PA) by

introducing Bacteriorhodopsin (bR), a natural proton

pumping photosystem and GaN nanowall network

(NWN), a direct band gap and corrosion-resistant

semiconductor. The experimental study reveals that

this combination of bR and GaN NWN has huge

potential as a light-activated sensitizer as well as

proton pumping source to achieve enhance

photocurrent density in hydrogen evolution reaction

(HER). Consequently, this synergistic effect in bR/GaN

NWN PA gives rise to largely enhanced applied bias

photon-to-current efficiency (ABPE) ~7.8% and

photocurrent density (28.74 mA/cm2 at 1.0 V vs

RHE). It is worth mentioning that the photocurrent

density of bR/GaN NWN, to the best of our

knowledge, is superior to previously reported bR-

based PAs and bio-photoelectric devices reported till

today for solar-to-hydrogen fuel generation.

Rotation Tunable Photocatalytic Properties of

ZnO/GaN Heterostructures School of Electronic Information Engineering, Key

Laboratory of Extraordinary Bond Engineering and

Advanced Materials Technology of Chongqing, Yangtze

Normal University, Chongqing 408100, China

School of Physical Science and Technology, Southwest

University, Chongqing 400715, China

Department of Physics, Chongqing University of Arts and

Sciences, Chongqing 402160, China

physica status solidi b

https://doi.org/10.1002/pssb.201900663

Using hybrid density functional calculations, we

explore how rotation angles can influence the

photocatalytic performance of two‐dimensional (2D)

ZnO/GaN heterostructures. Our results show that the

bandgaps and band alignments for ZnO/GaN

heterostructures can be tuned by rotation angles.

Rotated ZnO/GaN heterostructures are favorable for

visible light absorption. Band alignments of different

rotated ZnO/GaN heterostructures are severally

thermodynamically favorable for spontaneous

generation of hydrogen and oxygen with the pH

scope of 0‐14, 3‐14, 2‐14, 1‐14, 1‐14, and 4‐14.

Besides, the formed built‐in electric field across

ZnO/GaN heterostructure interface promotes

photogenerated carrier migration and inhibits

photogenerated carrier recombination. These factors

make rotated ZnO/GaN heterostructures promising

for visible light water‐splitting. Our findings pay a

new way to design 2D heterostructures used for

photocatalytic water‐splitting.

Surface Electronic Properties of Si‐Doped AlGaN and

Thermionic Emission Characteristics with Adsorption

of Alkali Metal Atoms Corporate Research and Development Center, Toshiba

Corporation 1, Komukai-toshiba-cho, Saiwai-ku, Kawasaki,

Kanagawa, 212-8584, Japan

physica status solidi a

https://doi.org/10.1002/pssa.201900719

A thermionic energy converter (TEC) is a heat engine

with a high theoretical efficiency, but a reduction in

operating temperature is required for practical

applications. Herein, the experimentally determined

thermionic conversion characteristics of Si‐doped

GaNEX | III-N Technology Newsletter No. 83 | 38

GaN films with Cs adsorption at 600 °C are reported.

Low‐temperature thermionic emission around 300 °C

is also reported for Si‐doped AlGaN surfaces with Cs

adsorption. This emission temperature is

considerably lower than the operating temperatures

of conventional systems with a metal emitter. The

AlGaN thin films are grown on n‐type 6H‐SiC

substrates, and it is confirmed by ultraviolet

photoelectron spectroscopy that the work function

decreases as the AlN mole fraction x in the AlGaN

samples is increased. Threshold temperatures of

thermionic emission decrease with increasing AlN

mole fraction and a corresponding reduction in the

work function.

Two dimensional ZnO/AlN composites used for

photocatalytic water-splitting: a hybrid density

functional study School of Electronic Information Engineering, Key

Laboratory of Extraordinary Bond Engineering and

Advanced Materials Technology of Chongqing, Yangtze

Normal University, Chongqing 408100, China

School of Physical Science and Technology, Southwest

University, Chongqing 400715, China

Institute for Advanced Study, Nanchang University,

Nanchang 330031, China

RSC Advances

https://doi.org/10.1039/C9RA06104E

Using hybrid density functionals, we study the

interfacial interactions and electronic properties of

ZnO/AlN composites with the consideration of

rotation angles and biaxial strains in order to enhance

the photocatalytic performance for water-splitting.

The different rotated composites, and −2% strained,

original, and 2% strained ZnO/AlN composites can be

easily prepared owing to the negative interface

formation energies. The bandgaps and band

alignments of ZnO/AlN composites can be

significantly tuned by biaxial strains. Particularly, the

appropriate bandgap for visible light absorption,

proper band alignment for spontaneous water-

splitting, and the formed electric field promoting

photoinduced carrier separation make the 2%

strained ZnO/AlN composite a potential candidate for

photocatalytic water-splitting. This work shines some

light on designing two dimensional heterostructured

photocatalysts.

Long-Term Stability Studies of a Semiconductor

Photoelectrode Protected by Gallium Nitride

Nanostructures

Journal of Materials Chemistry A

https://doi.org/10.1039/C9TA09926C

Improving the stability of semiconductor materials is

one of the major challenges for sustainable and

economic photoelectrochemical water splitting. N-

terminated GaN nanostructures have emerged as a

practical protection layer for conventional high

efficiency but unstable Si and III-V photoelectrodes,

due to their near-perfect conduction band-alignment,

which enables efficient extraction of photo-

generated electrons, and N-terminated surfaces,

which protects against chemical and photo-corrosion.

Here, we demonstrate that Pt-decorated GaN

nanostructures on n+-p Si photocathode can exhibit

ultrahigh stability of 3000 h (i.e., over 500 days for

usable sunlight ~5.5 h per day) at a large

photocurrent density (> 35 mA/cm2) under AM 1.5G

one-sun illumination. The measured applied bias

photon-to-current efficiency of 11.9%, with an

excellent onset potential of ~ 0.56 V vs. RHE, is one of

the highest values reported for a Si photocathode

under AM 1.5G one-sun illumination. This study

provides a paradigm shift for the design and

development of semiconductor photoelectrodes for

PEC water splitting: stability is no longer limited by

the light absorber, but rather by co-catalyst particles.

Built-in magnetic-electrical coupling enhances

photocatalytic performance of GaN/ZnO: a first

principle study College of Materials Science and Engineering, Inner

Mongolia University of Technology, Hohhot 010051, PR

China

College of Physics, Mudanjiang Normal University,

Mudanjiang 157011, PR China

Inner Mongolia Key Laboratory of Thin Film and Coatings,

Hohhot 010051, PR China

Physica B: Condensed Matter

https://doi.org/10.1016/j.physb.2019.411902

The electronic structure and transfer characteristic of

holes and electrons of GaN/ZnO heterojunction polar

interface with cation vacancy were calculated by first-

GaNEX | III-N Technology Newsletter No. 83 | 39

principle. Results show that the defect levels induced

by VZn in Zn-N interface are made up of N-2p and O-

2p states. The degeneracy of the defect levels and

intrinsic CBM reduce the band gap of system.

However, the defect level formed by the O-2p state

may become a recombination center, which is not

conducive to the separation of holes and electrons. In

contrast, the defect level induced by VGa in the Ga-O

interface does not become a recombination center,

and the larger built-in electric polarization intensity in

the interface can effectively prevent the

recombination of holes and electrons. In addition, the

spin polarization of p states weakly bound electrons

induced by cation vacancy leads to spin-band-

splitting in the conduction band, which reduces the

effective mass of electron and increases the transfer

velocity difference between holes and electrons, so

that photogenerated holes and electrons can be

effectively separated.

GaNEX | III-N Technology Newsletter No. 83 | 40

GROUP 7 - Materials, Technology and Fundamental Group leader: Jean-Christophe Harmand (LPN-CNRS)

NANO

Information selected by Jesús Zúñiga Pérez (CRHEA-CNRS)

Effect of KOH passivation for top-down fabricated

InGaN nanowire light emitting diodes Department of Microsystems Engineering, Rochester

Institute of Technology, Rochester, New York 14623, USA

Department of Electrical and Microelectronic

Engineering, Rochester Institute of Technology,

Rochester, New York 14623, USA

Journal of Applied Physics

https://doi.org/10.1063/1.5123171

Gallium nitride (GaN) nanowire (NW) light emitting

diodes (LEDs) are promising candidates for

microdisplay applications due to smaller dimensions

and potential for novel integration approaches. For

the commonly adopted top-down GaN NW

fabrication, the required dry etching steps tend to

result in surface states, leading to reduced radiative

recombination rates in LEDs. To passivate the

surface and tune the diameter of the NWs,

hydroxyl-based chemicals such as potassium

hydroxide (KOH) are widely used to treat the

surface of these nanostructures. However, studies

on the effects of temperature, concentration, and

the damage recovery aspects of hydroxyl etching of

GaN NWs are very scarce. These etching

parameters are of great importance for device

performance. Here, these effects are explored

thoroughly with a focus on the correlation of

InGaN/GaN NW LED performances to KOH etching

temperature, concentration, and time, together

with a fundamental crystallographic analysis. The

KOH concentration resulting in total removal of the

NW base tapering and a collimated etch profile for

InGaN NW LEDs was found to be 0.8 wt. % at a

temperature of 45 °C. A 20 min etch at 23 °C with a

0.1 wt. % KOH concentration will remove surface

states from a top-down fabricated NW LED to

recover up to 90% of the peak photoluminescence

(PL) intensity lost by the dry etch step. The

oscillation behavior in PL intensity with regard to

the KOH etch time has been demonstrated in

InGaN/GaN NW LEDs for the first time, which will

shed light upon the design and passivation of these

devices for microdisplays.

Subliming GaN into ordered nanowire arrays for

ultraviolet and visible nanophotonics Nanophotonics Center, NTT Corp., 3-1, Morinosato

Wakamiya, Atsugi, Kanagawa 243-0198, Japan

NTT Basic Research Laboratories, NTT Corp., 3-1,

Morinosato Wakamiya, Atsugi, Kanagawa 243-0198,

Japan

Université Côte d’Azur, CNRS, CRHEA,Rue B. Grégory,

06560 Valbonne, France

NTT Device Technology Laboratory, NTT Corp., 3-1,

Morinosato Wakamiya, Atsugi, Kanagawa 243-0198,

Japan

ACS Photonics

https://doi.org/10.1021/acsphotonics.9b01435

We report on the fabrication of ordered arrays of

InGaN/GaN nanowire quantum disks by a top-down

selective-area sublimation method. Using a

combination of two-dimensional molecular beam

epitaxy of InGaN/GaN quantum wells, electron-

beam lithography and ultra-high-vacuum

sublimation techniques, we demonstrate that the

position, geometry and dimensions of nanowires

can be finely controlled at nano-, micro- and macro-

scales. Relying on a large set of structural data, we

evaluate in particular the relative sublimation rates

of GaN crystal planes that drive the nanowire

formation, we assess the intrinsic limits of selective

area sublimation for the fabrication of NW arrays

and we evaluate the homogeneity of the process

across the wafer. Because the sublimation method

preserves the crystal quality of the NW material, we

show that InGaN/GaN NWs present good optical

properties, which can be leveraged for photonic

applications in the ultraviolet and the visible range.

In particular, we demonstrate that it is possible to

realize on the same wafer not only arrays of

nanowires that individually support room-

temperature lasing based on Fabry-Pérot

resonances, but also subwavelength nanowires that

GaNEX | III-N Technology Newsletter No. 83 | 41

we integrate in photonic crystals for the realization

of nanowire-induced nanocavities.

Mg and In Codoped p-type AlN Nanowires for pn

Junction Realization IRIG-PHELIQS, NPSC, University Grenoble Alpes, CEA,

38000 Grenoble, France

Grenoble INP, Institut Néel, University Grenoble Alpes,

CNRS, 38000 Grenoble, France

Institute of Materials Science, Universidad de Valencia,

Valencia, Spain

NanoLetters

https://doi.org/10.1021/acs.nanolett.9b01394

Efficient, mercury-free deep ultraviolet (DUV) light-

emitting diodes (LEDs) are becoming a crucial

challenge for many applications such as water

purification. For decades, the poor p-type doping

and difficult current injection of Al-rich AlGaN-

based DUV LEDs have limited their efficiency and

therefore their use. We present here the significant

increase in AlN p-doping thanks to Mg/In codoping,

which leads to an order of magnitude higher Mg

solubility limit in AlN nanowires (NWs). Optimal

electrical activation of acceptor impurities has been

further achieved by electron irradiation, resulting in

tunnel conduction through the AlN NW p–n

junction. The proposed theoretical scenario to

account for enhanced Mg incorporation involves an

easy ionization of In-vacancy complex associated

with a negative charging of Mg in In vicinity. This

leads to favored incorporation of negatively

charged Mg into the AlN matrix, opening the path

to the realization of highly efficient NW-based LEDs

in the DUV range.

Atomistic Modeling of Fine Structure Splitting in

InGaN/GaN Dot-in-Nanowire Structures for Use in

Entangled Photon Pair Generation Department of Electrical and Computer Engi-neering,

Southern Illinois University Carbondale, IL 62901 USA

IEEE Journal of Quantum Electronics

https://doi.org/10.1109/JQE.2019.2955938

Fine structure splitting (FSS) is a bottleneck in

quantum dot (QD) based solid-state entangled

photon pair sources for application in quantum key

distribution (QKD). In QDs, entangle photon pairs

are generated through a cascaded emission

process: biexciton to exciton to the ground state.

The FSS of the excitonic states destroys the

entanglement of the photon pairs, hence needs to

be eliminated. For numerical in-vestigation of FSS

and design optimization, a multiscale-multiphysics

many-body calculation is required. In this work, we

report the coupling of full configuration interaction

(FCI) method with 10-band (sp3s*-spin) tight-

binding (TB) model to calculate the excitonic

energetics of realistically-sized InGaN/GaN dot-in-

nanowire structures. Model benchmarking has been

done against a recently-reported InGaN/GaN

multiple quantum well (MQW) structure in the a-

plane orientation. Computational methodology of

implementing hexagonal-base truncated pyramid

shaped QD has been presented. The effects of QD

shape/thickness, material composition, and crystal

growth direction (polar c-plane and non-polar m-

plane and a-plane) on the FSS of InGaN/GaN based

photon emitters have been investigated.

Polarization profiles of the emitted photons from

the excitonic transitions have been derived

quantum me-chanically from transition dipole

moments. With the smallest FSS, the non-polar m-

plane device has been found to be most promising

for the QKD application.

Exploring the potential of c-plane indium gallium

nitride quantum dots for twin-photon emission Tyndall National Institute, University College Cork, Cork

T12 R5CP, Ireland

Department of Electrical Engineering, University College

Cork, Cork T12 YN60, Ireland

NanoLetters

https://doi.org/10.1021/acs.nanolett.9b03740

Non-classical light emission, such as entangled and

single-photon emission, has attracted significant

interest due its importance for future quantum

technology applications. In this work, we study the

potential of wurtzite (In,Ga)N/GaN quantum dots

for novel non-classical light emission namely twin-

photon emission. Our calculations, based on a fully

atomistic many body framework, reveal that the

combination of carrier localization due to random

alloy fluctuations in the dot, spin-orbit coupling

effects, underlying wurtzite crystal structure and

GaNEX | III-N Technology Newsletter No. 83 | 42

built-in electric fields lead to an excitonic fine

structure that is very different from more

"conventional" zincblende (In,Ga)As dots, which

have been used so far for twin photon emission. We

show and discuss here that the four energetically

lowest exciton states are all bright and emit linearly

polarized light. Furthermore, three of these

excitonic states are basically degenerate. All these

results are independent of the alloy microstructure.

Also, our calculations reveal large exciton binding

energies (>35 meV), which exceed the thermal

energy at room temperature. Therefore,

(In,Ga)N/GaN dots are very promising candidates to

achieve efficient twin photon emission, potentially

at high temperatures and over a wide emission

wavelength range.

Displacement Talbot lithography for nano-

engineering of III-nitride materials Department of Electrical & Electronic Engineering,

University of Bath, Bath, BA2 7AY, UK

Université Côte d’Azur, CNRS, CRHEA, rue B. Gregory,

06560, Valbonne, France

Ferdinand-Braun-Institut, Leibniz-Institut für

Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489,

Berlin, Germany

Technische Universität Berlin, Institute of Solid State

Physics, 10623, Berlin, Germany

Microsystems & Nanoengineering

https://doi.org/10.1038/s41378-019-0101-2

Nano-engineering III-nitride semiconductors offers

a route to further control the optoelectronic

properties, enabling novel functionalities and

applications. Although a variety of lithography

techniques are currently employed to nano-

engineer these materials, the scalability and cost of

the fabrication process can be an obstacle for large-

scale manufacturing. In this paper, we report on the

use of a fast, robust and flexible emerging

patterning technique called Displacement Talbot

lithography (DTL), to successfully nano-engineer III-

nitride materials. DTL, along with its novel and

unique combination with a lateral planar

displacement (D2TL), allow the fabrication of a

variety of periodic nanopatterns with a broad range

of filling factors such as nanoholes, nanodots,

nanorings and nanolines; all these features being

achievable from one single mask. To illustrate the

enormous possibilities opened by DTL/D2TL,

dielectric and metal masks with a number of

nanopatterns have been generated, allowing for the

selective area growth of InGaN/GaN core-shell

nanorods, the top-down plasma etching of III-

nitride nanostructures, the top-down sublimation of

GaN nanostructures, the hybrid top-down/bottom-

up growth of AlN nanorods and GaN nanotubes,

and the fabrication of nanopatterned sapphire

substrates for AlN growth. Compared with their

planar counterparts, these 3D nanostructures

enable the reduction or filtering of structural

defects and/or the enhancement of the light

extraction, therefore improving the efficiency of the

final device. These results, achieved on a wafer

scale via DTL and upscalable to larger surfaces, have

the potential to unlock the manufacturing of nano-

engineered III-nitride materials.

Mask-less MOVPE of arrayed n-GaN nanowires on

site- and polarity-controlled AlN/Si templates University of Duisburg-Essen, Dept. Components for High

Frequency Electronics, Faculty of Engineering, and

CENIDE, Duisburg, Germany

CrystEngComm

https://doi.org/10.1039/C9CE01151J

We present a novel approach to attain Ga-polar n-

GaN nanowires on n-Si(111)/AlN templates, by site-

and polarity-controlled metal organic vapor phase

epitaxy. A three-stage process is developed to (i)

form equally-sized Ga-polar GaN islands, (ii) change

the growth direction towards the vertical direction

and finally, to (iii) obtain continuous nanowire

epitaxy. Homogeneous islands are achieved by

minimizing parasitic nucleation and adjusting the

adatom diffusion length to the used nanoimprint

pattern. The influence of the carrier gas

composition on the polarity is studied, achieving

pure Ga-polarity by mostly using nitrogen carrier

gas. Enhancing the Si/Ga-ratio leads to an

amplification of the vertical growth, but also to a

reduced number of NWs. 100% growth is attained

by a height dependent V/III-ratio adjustment. The

results are supported by a qualitative model,

explaining how suppression of multi-pod, parasitic

and inhomogeneous crystallization can be realized

GaNEX | III-N Technology Newsletter No. 83 | 43

by trading off in situ SiNx passivation and localized

GaN growth.

Strongly Confined Excitons in GaN/AlN

Nanostructures with Atomically Thin GaN Layers

for Efficient Light Emission in Deep-Ultraviolet Ioffe Institute, St. Petersburg 194021, Russia

University of Notre Dame, Notre Dame, Indiana 46556,

USA

Université Montpellier, L2C, UMR 5221, 34095

Montpellier Cedex 5, France

NanoLetters

https://doi.org/10.1021/acs.nanolett.9b03517

Fascinating optical properties governed by

extremely confined excitons have been so far

observed in 2D crystals like monolayers of transition

metal dichalcogenides. These materials, however,

are limited for production by epitaxial methods.

Besides, they are not suitable for the development

of optoelectronics for challenging deep ultraviolet

spectral range. Here we present a single monolayer

of GaN in AlN as a heterostructure fabricated by

molecular beam epitaxy, which provides extreme

2D confinement of excitons, being ideally suited for

light generation in the deep ultraviolet. Optical

studies in the samples, supplemented by a group-

theory analysis and first-principle calculations,

evidence a giant enhancement of the splitting

between the dark and bright excitons due to short-

range electron-hole exchange interaction that is a

fingerprint of the strongly confined excitons. The

practical significance of our results is in the

observation of the internal quantum yield of the

room-temperature excitonic emission as high as

~75% at 235 nm.

NON POLAR / SEMI POLAR Information selected by

Philippe de Mierry Impact of 3D growth and SiN x interlayer on the

quality of (11–22) semi-polar GaN grown on m-

plane sapphire School of Electronic Science & Applied Physics, Hefei

University of Technology, 193 Tunxi Road, Hefei 230009,

People's Republic of China

School of Metallurgy and Materials, University of

Birmingham, Birmingham B15 2TT, United Kingdom

Anhui San'an Optoelectronics Co., Ltd., 8 Dongliang

Road, Wuhu 241000, People's Republic of China

Applied Physics Express

https://doi.org/10.7567/1882-0786/ab47b7

We report the growth of semi-polar (11−22) GaN

films with low defect densities on m-plane sapphire

substrates by incorporating a porous SiN x

interlayer in a three-stage growth process. The

linewidth of X-ray diffraction rocking curves for our

semi-polar GaN films decrease with increasing SiN x

deposition time. Cross-sectional transmission

electron microscopy analyzes confirm that the

proposed three-stage growth process greatly

reduces the semi-polar GaN threading dislocation

densities down to 7 × 108 cm−2.

Photoluminescence measurements demonstrate

that InGaN/GaN quantum wells grown on our semi-

polar GaN films provide peak intensities that are 26-

fold greater than those grown on semi-polar GaN by

a standard method.

Untwinned semipolar (10-13) Al x Ga1-x N layers

grown on m-plane sapphire Institute of Materials and Systems for Sustainability,

Nagoya University, Nagoya 464-8601, Japan

School of Engineering, Nagoya University, Nagoya 464-

8603, Japan

Akasaki Research Center, Nagoya University, Nagoya

464-8603, Japan

Semiconductor Science and Technology

https://doi.org/10.1088/1361-6641/ab4d2c

Heteroepitaxial growth of untwinned mono-

crystalline semipolar (10-13) Al x Ga1-x N layers on

(10-13) AlN template was investigated by

metalorganic vapour phase epitaxy. The templates

were initially deposited on (10-10) m-plane

sapphire substrates by directional sputtering.

Different Al/Ga ratios in gas phase were used to

adjust the AlN mole fraction over the entire range

of composition. All the layers show a triclinic

distortion in the wurtzite unit cell due to anisotropic

in-plane strain. The AlN mole fraction of the (10-13)

layers and c-plane co-loaded layers estimated by x-

ray diffraction is comparable. This is consistent both

GaNEX | III-N Technology Newsletter No. 83 | 44

with their comparable effective bandgap energy

estimated from optical transmission measurements

and their near band-edge emission energy obtained

from room-temperature photoluminescence. The

dependence of the bandgap and near band-edge

emission energies on the AlN mole fraction

indicates a bowing parameter of 0.9 eV.

Reduced nonradiative recombination in semipolar

green-emitting III-N quantum wells with strain-

reducing AlInN buffer layers Institute of Applied Physics, Technische Universität

Braunschweig, Mendelssohnstr. 2, 38106 Braunschweig,

Germany

Laboratory for Emerging Nanometrology, Technische

Universität Braunschweig, Langer Kamp 6a, 38106

Braunschweig, Germany

Centre de Recherche sur l'Hétéro-Epitaxie (CNRS-CRHEA),

Rue Bernard Grégory, 06560 Valbonne, France

Applied Physics Letters

https://doi.org/10.1063/1.5118853

Using strain-reducing partially relaxed AlInN buffer

layers, we observe reduced nonradiative

recombination in semipolar green-emitting

GaInN/GaN quantum wells. Since strain is a key

issue for the formation of defects that act as

nonradiative recombination centers, we aim to

reduce the lattice mismatch between GaInN and

GaN by introducing an AlInN buffer layer that can

be grown lattice-matched along one of the in-plane

directions of GaN, even in the semipolar (112⎯⎯2)

orientation. With the increasing thickness, the

buffer layer shows partial relaxation in one

direction and thereby provides a growth template

with reduced lattice mismatch for the subsequent

GaInN quantum wells. Time-resolved

photoluminescence measurements show reduced

nonradiative recombination for the structures with

a strain-reducing buffer layer.

Inhomogeneous Current Injection and Filamentary

Lasing of Semipolar (2021¯) Blue GaN‐Based

Vertical‐Cavity Surface‐Emitting Lasers with Buried

Tunnel Junctions Materials Department, University of California, Santa

Barbara, CA 93106, U.S.A

Department of Electrical and Computer Engineering,

University of California, Santa Barbara, CA 93106, U.S.A

physica status solidi a

https://doi.org/10.1002/pssa.201900718

Blue (202-1) semipolar vertical‐cavity

surface‐emitting lasers with a buried tunnel

junction current aperture are demonstrated under

continuous‐wave operation with a differential

efficiency of 4% and a threshold current of 2.7 mA

for a lasing mode at 452 nm. The effects of the

aperture diameter on these 9λ cavity length devices

are presented, showing that the differential

efficiency increases with aperture size, whereas the

threshold current density remains constant for

apertures larger than 10 μm. Filamentary lasing is

observed in the larger aperture sizes, and it is

suggested that this mode behavior is due to current

injection inhomogeneity across the aperture. This

theory is supported by the correlation between

optical nearfield images and thermal microscopy

images.

MATERIAL / CHARACTERIZATION / EQUIPMENT / NUMERICAL SIMULATION

Information selected by Agnès Trassoudaine (Université d'Auvergne), Yvon

Cordier and Mathieu Leroux (CRHEA-CNRS)

Electric-field-induced simultaneous diffusion of Mg

and H in Mg-doped GaN prepared using ultra-high-

pressure annealing Toyota Central R&D Labs., Inc., Yokomichi, Nagakute

480-1192, Japan

Nagoya University, Nagoya 464-8601, Japan

ULVAC, Inc., 2500 Hagisono, Chigasaki 253-8543, Japan

Institute of High Pressure Physics Polish Academy of

Sciences, 01-142 Warsaw, Poland

Applied Physics Express

https://doi.org/10.7567/1882-0786/ab4934

To investigate Mg diffusion during ultra-high-

pressure annealing, which activates Mg acceptors in

GaN, GaN samples with p–n junctions prepared via

epitaxial growth were annealed at 1573 K under 1

GPa. The profiles of Mg diffusion toward the

underlying n-type layer cannot be explained by a

GaNEX | III-N Technology Newsletter No. 83 | 45

simple diffusion model. We found that H atoms

diffused along with Mg atoms. By considering the

suppressed diffusion of positively charged

interstitial H atoms due to the electric field in the

depletion layer, we could better reproduce the Mg–

H diffusion profiles, suggesting that H atoms play a

key role in the Mg diffusion process.

Metalorganic chemical vapor deposition of

aluminum nitride on vertical surfaces Aalto University, Department of Electrical Engineering

and Automation, PO Box 13500, 00076 Aalto, Finland

Aalto University, Department of Electronics and

Nanoengineering, PO Box 13500, 00076 Aalto, Finland

Murata Electronics Oy, Myllynkivenkuja 6, 01621 Vantaa,

Finland

Journal of Crystal Growth

https://doi.org/10.1016/j.jcrysgro.2019.125345

Metalorganic chemical vapor deposited (MOCVD)

aluminum nitride (AlN) on vertical sidewalls can be

used to implement piezoelectric in-plane actuation

and sensing in microelectromechanical system

(MEMS) sensors. The AlN films should optimally

cover conformally the sidewalls and have good

crystal quality with c-axis oriented microstructure

for optimal piezoelectric properties. Previous

MOCVD AlN research has focused on using AlN as a

buffer layer for other III-nitrides and so far, AlN

growth has not been studied on large vertical

surfaces. In this study, AlN thin films were grown

using MOCVD on vertical sidewalls of fabricated

templates and the conformality and crystal quality

was characterized. The growth template fabrication

was optimized with respect to surface roughness,

the conformal coverage was analyzed by measuring

the thickness profiles of the films, and the crystal

quality was investigated using in-plane XRD and

TEM. The AlN films have good crystal quality

(FWHM 1.70°–3.44°) and c-axis orientation on

vertical Si(1 1 1) sidewalls. However, the

thicknesses of the films reduce approximately at a

rate of 0.8–1.2 nm/m down the sidewall. Lowering

the reactor pressure improved the conformal

coverage while changing the growth mode from

columnar to step-flow, which also improved the

film morphology.

Analysis of growth rate and crystal quality of AlN

epilayers by flow-modulated metal organic

chemical vapor deposition Key Laboratory of Semiconductor Materials Science,

Beijing Key Laboratory of Low Dimensional

Semiconductor Materials and Device, Institute of

Semiconductors, Chinese Academy of Sciences, Beijing,

100083, China

College of Materials Science and Opto-Electronic

Technology, University of Chinese Academy of Sciences,

Beijing, 101408, China

Superlattices and Microstructures

https://doi.org/10.1016/j.spmi.2019.106336

AlN templates have been grown on sapphire by

flow-modulated metal organic chemical vapor

deposition (MOCVD). By analyzing the TMAl duty

ratio R, TMAl utilization ratio β and parasitic

reaction ratio α, we obtained the quantitative

relationship between flow-modulated modes and

growth rate, and then proposed two kinds of flow-

modulated modes to increase the growth rate of

AlN. Besides, we found the continuous growth in

flow-modulated mode can transform the AlN

growth mode from the step-bunching growth into

the two-dimension growth and accordingly improve

the crystal quality of AlN. Finally, the AlN template

with a relatively fast growth rate (0.98 μm/h) and

flat surface morphology (RMS = 0.5 nm) was

obtained by NH3 pulse-flow mode with a small duty

ratio of NH3.

Accurate surface band bending determination on

Ga-polar n-type GaN films by fitting x-ray valence

band photoemission spectrum Vacuum Interconnected Nanotech Workstation (Nano-X),

Suzhou Institute of Nano-Tech and Nano-Bionics

(SINANO), Chinese Academy of Sciences (CAS), Suzhou

215123, China

Suzhou Institute of Nano-Tech and Nano-Bionics

(SINANO), Chinese Academy of Sciences (CAS), Suzhou

215123, China

AIP Advances

https://doi.org/10.1063/1.5120324

The surface band bending in Ga-polar n-type GaN

surfaces, as well as the effect of Si doping levels and

in situ Ar+ ion processing on band bending, was

GaNEX | III-N Technology Newsletter No. 83 | 46

systematically investigated. To precisely determine

the valence band maximum (VBM) of GaN beyond

instrumental and material surface environments by

XPS, a valence band feature fitting procedure based

on photoemission spectra and theoretical densities

of states has been developed. Poisson calculation

with quadratic depletion approximation on surface

potential has been used to model the band bending

and further correct the VBM energy. Then, the

actual surface band bending was correctly

evaluated. Upward band bending of 1.55 ± 0.03 eV

with highly Si doped n-GaN, which is about 0.88 eV

higher than that of the moderately doped sample,

was found. After in situ Ar+ plasma treatment, the

varying degree of band bending was observed

distinctly depending on the Si doping density. The

surface components associated with the Ga/N ratio

and Ga–O bonding concentration on the n-GaN

surface have been used to evaluate the

contribution to surface band bending.

Selective terahertz emission due to electrically

excited 2D plasmons in AlGaN/GaN

heterostructure Department of Physics of Semiconductors and

Nanoelectronics, Peter the Great St. Petersburg

Polytechnic University, 29 Polytechnicheskaya Str., St.

Petersburg 195251, Russia

Institute for Physics of Microstructures of RAS, Nizhny

Novgorod 603950, Russia

Department of Theoretical Physics, Institute of

Semiconductor Physics NASU, Kyiv 03028, Ukraine

Ioffe Institute, 26 Polytechnicheskaya Str., St. Petersburg

194021, Russia

Submicron Heterostructures for Microelectronics

Research and Engineering Center of RAS, 26

Polytechnicheskaya Str., St. Petersburg 194021, Russia

Department of Electronics and Nanoengineering, Aalto

University, P.O. Box 13500, Aalto FI-00076, Finland

Journal of Applied Physics

https://doi.org/10.1063/1.5118771

Terahertz radiation emission from an electrically

excited AlGaN/GaN heterostructure with a surface

metal grating was studied under conditions of two-

dimensional (2D) electron heating by the lateral

electric field. Intensive peaks related to

nonequilibrium 2D plasmons were revealed in the

terahertz emission spectra with up to 4 times

selective amplification of the radiation emission in

the vicinity of 2D plasmon resonance. This selective

emission was shown to be frequency-controllable

by the grating period. Exact spectral positions of the

2D plasmon resonances were preliminarily

experimentally detected with the help of

equilibrium transmission spectra measured at

various temperatures. The resonance positions are

in a satisfactory agreement with the results of

theoretical simulation of the transmission spectra

performed using a rigorous solution of Maxwell’s

equations. The effective temperature of hot 2D

electrons was determined by means of I–V

characteristics and their analysis using the power

balance equation. It was shown that for a given

electric field, the effective temperature of

nonequilibrium 2D plasmons is close to the hot 2D

electron temperature. The work may have

applications in GaN-based electrically pumped

emitters of terahertz radiation.

Impact of dislocations on the thermal conductivity

of gallium nitride studied by time-domain

thermoreflectance Department of Electrical and Computer Engineering,

University of Illinois at Urbana-Champaign, Urbana,

Illinois 61801, USA

Nick Holonyak, Jr. Micro and Nanotechnology

Laboratory, University of Illinois at Urbana-Champaign,

Urbana, Illinois 61801, USA

Journal of Applied Physics

https://doi.org/10.1063/1.5126970

GaN thermal conductivity (κGaN) of hydride vapor

phase epitaxy grown GaN (HVPE GaN), high nitride

pressure grown GaN (HNP GaN), and metal-organic

chemical vapor deposition grown GaN on sapphire

(GaN/sapphire) and on Si(111) (GaN/Si) are

measured as 204.7 (±4.6), 206.6 (±6.8), 191.5

(±10.5), and 164.4 (±3.2) W/m K, respectively, using

the time-domain thermoreflectance technique.

Dislocation densities (σD) of HVPE GaN, HNP GaN,

GaN/sapphire, and GaN/Si are measured as 4.80

(±0.42) × 105, 3.81 (±0.08) × 106, 2.43 (±0.20) × 108,

and 1.10 (±0.10) × 109 cm−2, respectively, using

cathodoluminescence and X-ray diffraction studies.

Impurity concentrations of Si, H, C, and O are

measured by secondary ion mass spectroscopy

GaNEX | III-N Technology Newsletter No. 83 | 47

studies. The relationship between κGaN and σD is

modeled through a new empirical model

κGaN = 210 tanh0.12(1.5 × 108/σD). A modified

Klemens's model, where dislocation induced

scattering strength is increased, is proposed to

explain the experimental rate of decrease in κGaN

with increasing σD. Overall, this work reports how

κGaN of heteroepitaxially-grown GaN can be

estimated based on σD, providing key design

guidelines for thermal management in GaN

semiconductor devices.

Thermal conductivity of crystalline AlN and the

influence of atomic-scale defects Electrical Engineering, Stanford University, Stanford,

California 94305, USA

Thermal and Fluid Engineering, University of Twente,

Enschede 7500 AE, Netherlands

Electrical and Computer Engineering, Cornell University,

Ithaca, New York 14853, USA

Mechanical Engineering, Stanford University, Stanford,

California 94305, USA

Stanford Institute for Materials and Energy Sciences,

SLAC National Accelerator Laboratory, Menlo Park,

California 94025, USA

Physics and Astronomy, University of California, Los

Angeles, California 90095, USA

LITEN, CEA-Grenoble, 17 Avenue des Martyrs, 38054

Grenoble, France

Centre for Modeling and Simulation (CMS), Savitribai

Phule Pune University, Ganeshkhind, Pune 411007,

Maharashtra, India

Materials Science and Engineering, Stanford University,

Stanford, California 94305, USA

Materials Science and Engineering, Cornell University,

Ithaca, New York 14853, USA

Journal of Applied Physics

https://doi.org/10.1063/1.5097172

Aluminum nitride (AlN) plays a key role in modern

power electronics and deep-ultraviolet photonics,

where an understanding of its thermal properties is

essential. Here, we measure the thermal

conductivity of crystalline AlN by the 3ω method,

finding that it ranges from 674 ± 56 Wm−1 K−1 at

100 K to 186 ± 7 Wm−1 K−1 at 400 K, with a value of

237 ± 6 Wm−1 K−1 at room temperature. We

compare these data with analytical models and

first-principles calculations, taking into account

atomic-scale defects (O, Si, C impurities, and Al

vacancies). We find that Al vacancies play the

greatest role in reducing thermal conductivity

because of the largest mass-difference scattering.

Modeling also reveals that 10% of heat conduction

is contributed by phonons with long mean free

paths (MFPs), over ∼7 μm at room temperature,

and 50% by phonons with MFPs over ∼0.3 μm.

Consequently, the effective thermal conductivity of

AlN is strongly reduced in submicrometer thin films

or devices due to phonon-boundary scattering.

An in situ monitored and controlled etch process

to suppress Mg memory effects in MOCVD GaN

growth on Si substrate Centre for Nano Science and Engineering, Indian Institute

of Science, Bangalore 560012, India

Department of Electrical Communication Engineering,

Indian Institute of Science, Bangalore 560012, India

Materials Research Centre, Indian Institute of Science,

Bangalore 560012, India

Semiconductor Science and Technology

https://doi.org/10.1088/1361-6641/ab5006

Mg is the most common p-type dopant in III-nitride

devices and is becoming increasingly important in

the design and development of transistors for

power applications. The diffusion of Mg atoms to

adjacent layers during growth has been a persistent

problem. We report on a simple method involving

in situ etching by hydrogen, the most commonly

used carrier gas in nitride growth, for suppressing

Mg diffusion. This method can be implemented

during growth itself without removing the wafer

from the chamber and can be controlled by in situ

monitoring. A Mg concentration decay rate of 24

nm/dec, is reported for the etched sample

compared to 160 nm/dec for the unetched one. An

increase in 2DEG mobility in AlGaN/GaN HEMT

structures on silicon substrate from 591 cm2 V−1

s−1 for the unetched sample to 1214 cm2 V−1 s−1

for the etched sample was observed. Capacitance–

voltage studies to understand the effect of diffused

Mg atoms on conduction channel are also reported.

GaNEX | III-N Technology Newsletter No. 83 | 48

High-mobility two-dimensional electron gases at

AlGaN/GaN heterostructures grown on GaN bulk

wafers and GaN template substrates School of Electrical and Computer Engineering, Cornell

University, Ithaca, NY 14853, United States of America

Department of Materials Science and Engineering,

Cornell University, Ithaca, NY 14853, United States of

America

Kavli Institute for Nanoscale Science, Cornell University,

Ithaca, NY 14853, United States of America

Applied Physics Express

https://doi.org/10.7567/1882-0786/ab512c

We report a comparative study of the mobility of

two-dimensional electron gases (2DEG) formed at

AlGaN/GaN heterostructures by simultaneously

growing on substrates with very different

dislocation densities. The mobility is seen to depend

on the 2DEG charge density directly, but

surprisingly, dislocations do not cause a discernible

impact on the mobility of the samples within the

measured region <25 000 cm2 V−1 s−1. This

experimental observation questions the generally

accepted belief that dislocations are one of the

dominant low-temperature scattering mechanisms

for low-density 2DEG at AlGaN/GaN structures.

Experimental Determination of Velocity-Field

Characteristic of Holes in GaN Department of Electrical Engineering, Stanford

University, CA, 94305 USA

Department of Electrical and Computer Engineering,

University of California, Davis, CA, 95616 USA

IEEE Electron Device Letters

https://doi.org/10.1109/LED.2019.2953873

This study presents a photo-assisted method to

measure the drift velocity of carriers in

semiconductors, and successfully used to determine

the drift velocity of holes in GaN. A p-i-n diode with

a buried p-type layer was designed and fabricated

on a free-standing GaN substrate. By reverse-

biasing the p-i-n diode and illuminating the cathode

layer using an ultraviolet light simultaneously,

photo-generated holes were injected into the

depletion region and accelerated by the electric

field to reach the saturation velocity. The drift

velocity (vd). electric field (E) characteristic can be

obtained from the photocurrent induced by photo-

generated holes. The measured hole drift velocity

can be written as vd= µLF E/[1+(µLF E/vsat)β]1/β,

where µLF=17 cm2/Vs is the low-field hole mobility,

vsat=6.63×106 cm/s is the saturation velocity,

β=1.75 is the fitting parameter. The method

presented in this study is a unique way of

determining the saturation drift velocity of holes in

GaN.

Modeling the simultaneous effects of thermal and

polarization in InGaN/GaN based high electron

mobility transistors Department of Physics, College of Science, Majmaah

University, Al Zulfi, 11932, Saudi Arabia

Electronics and Microelectronics Laboratory, Faculty of

Science of Monastir, University of Monastir, Monastir,

5019, Tunisia

Quantum and Statistical Physics Laboratory, Faculty of

Sciences of Monastir, University of Monastir, Monastir,

5019, Tunisia

Laboratoire de Matière Condensée et Sciences

Interdisciplinaires (LaMCScI), Group of Optoelectronic of

Semiconductors and Nanomaterials, ENSET, Mohammed

V University in Rabat, Morocco

Université de Lorraine, LCP-A2MC, F-57000, Metz, France

Department of Mechanical and Industrial Engineering,

College of Engineering, Majmaah University, Al-Majmaah

11952, Saudi Arabia

Computer Science Department, College of Science and

Humanities at Alghat, Majmaah University, Majmaah

11952, Saudi Arabia

Computer and Embedded System Laboratory, Sfax

University, Sfax, 3011, Tunisia

Optik

https://doi.org/10.1016/j.ijleo.2019.163883

In this paper, we propose the modeling of the two-

dimensional electron gas (2DEG) density in

InGaN/GaN hetero-interface based high electron

mobility transistors (HEMT). The Schrodinger-

Poisson equations, as well as the polarization-

induced charges, have been utilized. The

temperature effect on the effective mass, band gap

energy, dielectric constant and the lattice thermal

expansion is taken into account. Our numerical

calculation shows that the 2DEG density decreases

with temperature. This is due to the shrinkage of

the conduction band offset at high temperatures.

GaNEX | III-N Technology Newsletter No. 83 | 49

The improvement of the sheet carrier density and

the carrier confinement at the InGaN/GaN hetero-

interface based heterostructures is made at low

temperature.

Influence of plasma-activated nitrogen species on

PA-MOCVD of InN Department of Physics and Astronomy, Georgia State

University, Atlanta, Georgia 30303, USA and Center for

Nano-Optics, Georgia State University, Atlanta, Georgia

30303, USA

Department of Geosciences, Georgia State University,

Atlanta, Georgia 30303, USA

Applied Physics Letters

https://doi.org/10.1063/1.5126625

We report on the influence of various plasma

species on the growth and structural properties of

indium nitride in plasma-assisted metalorganic

chemical vapor deposition. Atomic emission

spectroscopy was used to quantify the molecular,

neutral, and ionized nitrogen species

concentrations above the growth surface.

Reflectance and Raman spectroscopy and X-ray

diffraction techniques were used to characterize

the grown InN films. It has been found that ionized

rather than molecular or neutral nitrogen species is

positively correlated with the InN growth rate. We

conclude that InN formation in the present case is

due to the chemical combination of atomic nitrogen

ions with indium.

Improving Ni/GaN Schottky diode performance

through interfacial passivation layer formed via

ultraviolet/ozone treatment Department of Electronics and Electrical Convergence

Engineering, Hongik University, Sejong, 30016, Republic

of Korea

School of Electronics Engineering, Kyungpook National

University, Daegu, 41566, Republic of Korea

Current Applied Physics

https://doi.org/10.1016/j.cap.2019.11.017

Electrical passivation has a significant effect on

metal-semiconductor (MS) device operations

including performance and reliability. In this study,

the improvement in performance of Ni/GaN

Schottky diodes (SDs) through an ultraviolet/ozone

(UV/O3) interface treatment is investigated and the

mechanism of carrier conduction at the MS junction

interfaces is analyzed. The formation of surface

oxide layer at the MS interface through the UV/O3

treatment is confirmed by the measurements using

X-ray photoelectron spectroscopy, contact angle,

and atomic force microscopy. The atomic intensity

and surface energy increased and surface

roughness improved through the implementation of

oxide layer. Electrical measurements reveal reduced

leakage and improved breakdown voltage and are

used to determine the Schottky barrier height and

Richardson constant of the Ni/GaN MS SDs. The

enhancement in the entire performance of the MS

SDs is attributed to the passivation of defect

centers at the dislocation-related pits through the

formation of oxide layer with the UV/O3 treatment,

which thereby improves the carrier transfer

properties of Ni/GaN SDs.

Field Dependent Ultrafast Carrier Dynamics in

InGaN/GaN p-i(MQW)-n Structure Key Laboratory of Polar Materials and Devices,

Department of Optoelectronics, East China Normal

University, Shanghai 200241, P. R. China

Department of Physics, Beijing University of Science and

Technology, Beijing 100083, P. R. China

Superlattices and Microstructures

https://doi.org/10.1016/j.spmi.2019.106354

Field dependent ultrafast carrier dynamics in

InGaN/GaN multiple quantum wells (MQW)

embedded within a p-i-n structure (InGaN/GaNp-

i(MQW)-n) was systematically investigated by

photoluminescence (PL), time-resolved PL and

transient differential reflectivity measurements. We

observed two PL peaks (centered at 450nm and

500nm) originated from MQW and localized defect

states. Excitation density dependent PL spectra

shows that the amplified spontaneous emission

participates in the quantum well emission.

Surprisingly, time-resolved PL clearly exhibits that

quantum well emission has an extremely long decay

time, which is much slower than the lower energy

peak from defect states. We infer that the built-in

PN field affects dominantly the carrier

recombination more than the piezoelectric

polarization field. The distinct excitation-dependent

GaNEX | III-N Technology Newsletter No. 83 | 50

decay kinetic allows us to identify the dynamic

interplay of screening and descreening effect by

photo-generated carriers. Additionally transient

reflectivity measurements also exhibit that carrier

thermalization process becomes faster with

increasing excitation density, which could be due to

the amplified spontaneous emission.

Confirmation of the compensation of

unintentional donors in AlGaN/GaN HEMT

structures by Mg-doping during initial growth of

GaN buffer layer Raja Ramanna Centre for Advanced Technology, Indore,

452013, Madhya Pradesh, India

Homi Bhabha National Institute, Training School

Complex, Anushakti Nagar, Mumbai, 400094, India

Journal of Luminescence

https://doi.org/10.1016/j.jlumin.2019.116904

Effect of partial Mg doping on the compensation of

unintentional donors at epilayer/template interface

and in the GaN channel layer of AlGaN/GaN High

Electron Mobility Transistor (HEMT) structures is

investigated. Photoluminescence excitation

spectroscopy and surface photovoltage

spectroscopy measurements reveal the signature of

high density of unintentional shallow donors and

deep level defects throughout the GaN buffer layer

along with a strong dominance at the GaN/Fe-GaN

template interface. Mg doping during the initial

growth of GaN buffer layer on Fe-GaN template is

found to compensate unintentional donors which

therefore reduces the density of deep defects. Hall

measurements also confirm systematic

improvement in the electronic transport properties

of AlGaN/GaN HEMT for an optimized Mg doping.

Further, Mg-doping driven enhancement of 2-

dimensional electron gas confinement at

AlGaN/GaN interface is also observed in the

spectroscopy measurements. It is shown that the

electrical and optical properties can be improved by

an optimized Mg-doping of the initial part of GaN

buffer layer in AlGaN/GaN HEMT structures.

In Situ Synchrotron X-ray Diffraction Reciprocal

Space Mapping Measurements in the RF-MBE

Growth of GaInN on GaN and InN Department of Applied Physics, School of Advanced

Engineering, Kogakuin University, Tokyo192-0015, Japan

Synchrotron Radiation Research Center, National

Institutes for Quantum and Radiological Science and

Technology (QST), Hyogo 679-5148, Japan

Department of Electrical & Electronic Engineering,

Ritsumeikan University, Kyoto 525-8577, Japan

Crystals

https://doi.org/10.3390/cryst9120631

In this work, in situ synchrotron X-ray diffraction

reciprocal space mapping (RSM) measurements

were carried out for the radio-frequency plasma-

assisted molecular beam epitaxy (RF-MBE) growth

of GaInN on GaN and InN layers, which were also

grown by RF-MBE on commercialized GaN/c-

sapphire templates. In situ XRD RSM measurements

were performed using an MBE apparatus directly

coupled to an X-ray diffractometer at the beamline

of the synchrotron radiation facility SPring-8. It was

observed in situ that both lattice relaxation and

compositional pulling occurred during the initial

growth stage, reducing the strain of GaInN on GaN

and InN. Different initial growth behaviors of GaInN

on GaN and InN were also observed from the

results of the evolution of GaInN integrated peak

intensities.

Suppression of Green Luminescence of

Mg‐Ion‐Implanted GaN by Subsequent

Implantation of Fluorine Ions at High Temperature ASEE Postdoctoral Fellow residing at U.S. Naval

Research Laboratory, Washington, DC, 20375, USA

U.S. Naval Research Laboratory, Washington, DC, 20375,

USA 3Dept. of Physics, University of Notre Dame, Notre

Dame, IN, 46556, USA

NRC Postdoctoral Associate residing at U.S. Naval

Research Laboratory, Washington, DC, 20375, USA

physica status solidi b

https://doi.org/10.1002/pssb.201900554

Gallium nitride (GaN) samples implanted with

magnesium (Mg) and fluorine (F) ions were

investigated by photoluminescence (PL)

measurement. In low‐temperature PL

GaNEX | III-N Technology Newsletter No. 83 | 51

measurements, the characteristic green

luminescence (GL) band attributable to nitrogen

vacancies (VNs) is observed in Mg‐ion‐implanted

GaN. Since VNs are likely to act as donors,

suppressing their formation is essential to realizing

p‐type conductivity. The energy required for a F

impurity to replace VN in GaN and eventually form

F on a N site decreases when the Fermi level

approaches to the valence band maximum, and

therefore F was employed as a subsequent

implantation element to compensate for VN. The

GL band peak disappeared upon implanting Mg and

F ions at a high temperature and adjusting the F

concentration to an appropriate value. This result

suggests that VNs generated by Mg ion

implantation can be suppressed by using an

element with a lower formation energy than VN.

Deep‐Level Defects and Impurities in InGaN Alloys Materials Department, University of California, Santa

Barbara, California 93106-5050, USA

Center for Computational Materials Science,US Naval

Research Laboratory, Washington, D.C. 20375, USA

Department of Physics and Astronomy, Stony Brook

University, Stony Brook, New York 11794-3800, USA

Center for Computational Quantum Physics, Flatiron

Institute, 162 5th Avenue, New York, NY 10010

Department of Materials Science and Engineering,

University of California, Berkeley, CA 94720-1760, USA

Center for Physical Sciences and Technology (FTMC),

Vilnius LT-10257, Lithuania

physica status solidi b

https://doi.org/10.1002/pssb.201900534

In this study, density functional theory calculations

with a hybrid functional are used to examine the

charge‐state transition levels of native point defects

and impurities in InGaN alloys, with the goal of

identifying centers that play a role in

defect‐assisted recombination. Explicit alloy

calculations are used to monitor the dependence of

defect levels on indium content and distribution of

In atoms. The relative shift (or lack thereof) of the

charge‐state transition levels of the different

defects is explained by the atomic character of the

defect state and whether it is derived from

valence‐band or conduction‐band states of the host

material or acts as an atomic‐like impurity. The

various possible atomic configurations of In and Ga

cations for a given composition of InGaN lead to a

distribution of charge‐state transition levels.

Defects on the nitrogen site lead to a larger spread

in levels compared with defects on the cation site.

Role of Capping Material and GaN Polarity on Mg

Ion Implantation Activation

physica status solidi a

https://doi.org/10.1002/pssa.201900789

Ion implantation of magnesium for p‐type GaN

presents many opportunities, however, activation

has proven difficult due to the decomposition of

GaN at relevant annealing temperatures. Here we

present testing the efficacy of multiple in‐situ and

ex‐situ caps based on aluminum nitride and silicon

nitride for GaN protection during annealing.

Photoluminescence shows better activation for

in‐situ MOCVD grown aluminum nitride caps

compared to ex‐situ sputtered aluminum nitride

and the best performance by ex‐situ PECVD silicon

nitride. Furthermore, only samples annealed at the

highest temperatures tested showed preferential

growth of UV luminescence to yellow‐green

luminescence reinforcing the need for better

capping solutions and higher temperature

annealing.

Effect of Wafer Off‐Angles on Defect Formation in

Drift Layers Grown on Free‐Standing GaN

Substrates Graduate School of Electrical and Electronics

Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui

910–8507, Japan

Sciocs Company Ltd., Hitachi-Shi, Ibaraki 319-1418, Japan

Research Centre for Micro-Nano Technology, Hosei

University, 3-11-15 Midori-cho, Koganei, Tokyo 184–

0003, Japan

physica status solidi b

https://doi.org/10.1002/pssb.201900561

The effect of the surface off‐angle toward either the

a‐ or m‐axis on the defect formation is

characterized using deep‐level transient

spectroscopy (DLTS) in conjunction with the carrier

concentration for Ni Schottky contacts formed on

GaNEX | III-N Technology Newsletter No. 83 | 52

n‐GaN drift layers. In both noncontact and

conventional capacitance–voltage results, off‐angle

dependence on carrier concentration is observed.

For all samples, a large dominant peak appears at

approximately 270 K in the DLTS spectra and is

attributed to E3 (EC − 0.57–0.61 eV) defects. Carbon

atoms can act as carrier compensators and form E3

defects. These results can be interpreted based on

how C incorporation during crystal growth depends

on the off‐angle.

Growth of AlGaN/InGaN/GaN Heterostructure on

AlN Template/Sapphire Wide-gap semiconductor group, National Institute for

Materials Science, Tsukuba, 305-0044, Japan

High Magnetic Field Measurement Group, National

Institute for Materials Science, Tsukuba, 305-0003, Japan

Department of Condensed Matter Physics, Graduate

School of Science, Hokkaido University, Sapporo 060-

0810, Japan

Department of Electric Engineering and Electronics,

Graduate School of Engineering, Kogakuin University,

Hachioji, Tokyo 192-0015, Japan

physica status solidi b

https://doi.org/10.1002/pssb.201900524

GaN films are grown directly on AlN

templates/sapphire substrates without using

low‐temperature (LT) buffer layers by metalorganic

chemical vapor deposition. AlN templates are

complimentarily deformed at the initial growth of

GaN, adjusting the a‐lattice constant and tilting

crystal orientation slightly. Compared with the film

on sapphire substrates using an LT buffer layer, the

GaN on the AlN template forms a smoother surface

and has better crystalline quality after a shorter

growth time at a lower temperature. Higher‐quality

InGaN films on the GaN/AlN template are

subsequently grown to optimize the thickness

exhibiting the minimum Urbach energy which is

evaluated by photothermal deflection

spectroscopy. A high‐quality AlGaN/InGaN

heterostructure is fabricated in which the

Shubnikov–de Haas oscillation can be clearly

observed from the electron gas of the InGaN

channel at the interface.

The Influence of Ga–OH Bond at Initial GaN

Surface on the Electrical Characteristics of

SiO2/GaN Interface Nara Institute of Science and Technology, Ikoma Nara,

Japan

physica status solidi b

https://doi.org/10.1002/pssb.201900368

Herein, the influence of the Ga–OH bond at the GaN

surface on the electrical characteristics of the

SiO2/GaN metal‐oxide semiconductor structure is

investigated. The GaN surface is modified by three

different surface treatments (O2 annealing, wet

annealing, and ultraviolet [UV]/O3 treatment). The

Ga–OH bond is evaluated by X‐ray photoelectron

spectroscopy and characterized by capacitance–

voltage (CV) measurements and a positive bias

stress test. Increasing the ratio of Ga–OH bonds at

the SiO2/GaN interface decreases the net fixed

charge at the SiO2/GaN interface in the CV

measurements and increases the voltage shift in the

stress test. Therefore, the Ga–OH bond at the

SiO2/GaN interface develops a negative charge and

behaves as an electron trap. The undesirable

influence of the Ga–OH‐related traps is reduced by

low‐temperature annealing.

Prediction of dislocation density in AlN or GaN

films deposited on (0001) sapphire Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMAP,

Grenoble, France

Sil’Tronix Silicon Technologies, Archamps, France

Journal of Materials Science

https://doi.org/10.1007/s10853-019-04240-x

The origin of threading dislocations (TDs) in nitride

films is not completely understood but it is well

established that they degrade the film properties.

This work investigates the assumption that they

arise from the interface between the film and

sapphire substrate owing to small in-plane rotations

between nitride domains. Bollmann’s formalism is

first used to determine the characteristics of

dislocations at the nitride film/sapphire interface

that compensate both for the parametric misfit and

a small in-plane rotation of the film as frequently

observed. It is shown that the dislocation density

GaNEX | III-N Technology Newsletter No. 83 | 53

and line direction depend on the rotation angle.

When islands grow and coalesce in the nucleation

layer, some interfacial dislocations orientate along

[0001] in the boundaries between domains and

transform to so-called TDs. The amount of TDs lying

in the boundaries between nitride domains is

calculated as a function of the rotation angle.

Estimations of TD density in the nucleation layer are

deduced for a range of domain sizes and compared

with experimental values of the literature.

Study of electronic properties on the n-GaN (0001)

surface with points defects Department of Optoelectronic Technology, School of

Electronic and Optical Engineering, Nanjing University of

Science and Technology, Nanjing, People’s Republic of

China

Applied Physics A

https://doi.org/10.1007/s00339-019-3142-3

The influence of defects on the surface of the semiconductor is irreversible. The influence of

intrinsic point defects on the electronic properties of n-doped GaN (0001) surface is studied based on the first principles. The results show that, the N interstitial defect (Ni) and Ga Vacancy (VGa) are the more easily formed in the case of Si doping. The defect level generated by an appropriate amount of defects contributes to the transition of electrons, thereby improving the n-type conductivity characteristics. In particular, the Ga vacancy makes the work function drop significantly, which promotes the emission of electrons. However, once the defects inside the material exceed a certain level, any defects will play a counterproductive role. This paper could provide some guidance for the preparation of n-GaN optoelectronic devices.

GaNEX | III-N Technology Newsletter No. 83 | 54

PRESS RELEASE Technical and economic information selected by Knowmade

ELECTRONICS

RF GaN market growth to accelerate to over $1.7bn in 2023: SEDI, Wolfspeed and Qorvo to benefit SemiconductorToday

Revenue from RF gallium nitride (GaN)-enabled devices grew nearly 22% in 2018 and will accelerate, surpassing

$1.7bn in 2023, forecasts the Strategy Analytics Advanced Semiconductor Applications (ASA) report ‘RF GaN

Market Forecast: 2018 - 2023 (Data Tables)’. The drivers for this growth will be the continuing deployments of

4G and emerging 5G base-stations, along with a variety of defense applications.

“Base stations represent the largest source of GaN revenue,” notes Eric Higham, director of the Advanced

Semiconductor Applications (ASA) service and the Advanced Defense Systems (ADS) service. “Trade tensions

between the US and China remains a wildcard, but Sumitomo Electric Device Innovations and Wolfspeed will

remain the dominant GaN suppliers for base-station applications,” he adds. “The defense market, primarily

radar and communications applications, is seeing strong growth from new systems and major platform

upgrades. This is also providing fuel for the GaN growth engine and should bode well for companies like Qorvo

and Wolfspeed.”

Transphorm ships over half a million GaN power devices for multi-kW-class applications SemiconductorToday

Transphorm Inc of Goleta, near Santa Barbara, CA, USA — which designs and manufactures JEDEC- and AEC-

Q101-qualified 650V gallium nitride (GaN) field-effect transistors (FETs) — says it has shipped more than

500,000 high-voltage GaN FETs.

Customers in the broad industrial, infrastructure & IT and PC gaming markets have publicly announced in-

production devices built with Transphorm’s GaN technology, illustrating the rising confidence in GaN solutions,

says the firm.

In fact, industry analyst firm IHS Markit Technology (now a part of Informa Tech) forecasts that total GaN power

discrete, module and system IC revenue will reach $1.2bn by 2028 (‘SiC & GaN Power Semiconductors Report’,

May 2019). About $750m of that (almost two-thirds of the total market) will be driven by high-voltage GaN

solutions.

“We came to market with the most robust, two-chip normally-off device at a time when the industry was more

familiar with single-chip normally-off silicon MOSFETs,” says Transphorm’s co-founder & chief operating officer

Primit Parikh. “As proven by our public momentum and also that of other reputable manufacturers like Power

Integrations in the consumer adapter space, the two-chip normally-off GaN solution is the most practical high-

voltage GaN FET design today,” he adds. “In fact, it’s this design that enables Transphorm’s GaN to deliver high

performance with strong robustness, which has led to more than 5 billion hours (with <2 FIT) of field reliability

data to date.”

GaNEX | III-N Technology Newsletter No. 83 | 55

Transphorm says that its adoption continues to be driven largely by the quality and reliability (Q+R) of its

products, which is backed by its robust normally-off GaN platform, strong control of its epitaxial process, and

manufacturing capability — positioned to meet the volume and quality requirements of various cross-industry

markets from consumer adapters to automotive.

“Following our success in the core higher-power markets targeted by GaN, we’re also working with customers in

fast-growing markets that are underserved by silicon such as consumer adapters and set-top boxes,” says Philip

Zuk, VP of worldwide technical marketing & North American sales. “Consider that the majority of products

we’ve shipped to date were targeted for higher-power applications. Those 500,000-plus 650V FETs equate to

more than 4 million lower-power (sub-100W) FETs, demonstrating our volume production capabilities.”

A year ago, Transphorm released the first complete set of validation data for high-voltage GaN power

semiconductors. The firm has now formally released its latest field reliability data. With more than 5 billion

hours in the field, Transphorm’s GaN technology currently has a <2.0 FIT rate at <19.8 PPM per year.

Nexperia enters GaN FET market SemiconductorToday

Nexperia BV of Nijmegen, Netherlands, which manufactures discrete and MOSFET components and analog &

logic ICs, has announced its entry into the gallium nitride (GaN) field-effect transistor (FET) market with the

introduction of the 650V GAN063-650WSA, which has a gate-source voltage (VGS) of +/-20V, a temperature

range of -55°C to +175°C, a low on-resistance (RDS(on)) of down to 60mΩ, and fast switching to offer very high

efficiency.

In April 2018, Cree Inc of Durham, NC, USA signed a non-exclusive, worldwide, royalty-bearing patent license

agreement that provided Nexperia with access to its GaN power device patent portfolio, addressing device

structures, materials and processing improvements, and packaging technology.

Nexperia is targeting high-performance application segments including hybrid and all-electric vehicles (xEV),

data centers, telecom infrastructure, industrial automation and high-end power supplies. The firm says that its

GaN-on-silicon process is robust and mature with proven quality and reliability, and that it is highly scalable as

wafers can be processed in existing silicon fabrication facilities. Also, the device is available in the industry-

standard TO-247, allowing the benefit of GaN’s performance in a familiar package.

“This is a strategic move for Nexperia into the high-voltage area, and we can now deliver technology suitable for

xEV power semiconductor applications,” says Toni Versluijs, general manager of Nexperia MOS Business Group.

“Our GaN is a technology that is ready for volume production, and with scalability to meet high-volume

applications,” he adds. “The automotive sector is a key focus for Nexperia and one which is forecast to grow

significantly for two decades as electric vehicles replace those powered by traditional internal combustion

engines as the preferred means of personal and public transport.”

The GAN063-650WSA GaN FET is the first in a portfolio of GaN devices that Nexperia is developing to address

the automotive, communication infrastructure and industrial markets.

GaNEX | III-N Technology Newsletter No. 83 | 56

SweGaN, IEMN and Linköping University unveil Transmorphic Heteroepitaxy GaN-on-SiC growth process for power devices SemiconductorToday

A project funded by the European Union’s Horizon 2020 research and innovation program has contributed to

custom gallium nitride on silicon carbide (GaN-on-SiC) epitaxial wafer manufacturer SweGaN AB of Linköping,

Sweden collaborating with Linköping University and IEMN (a French research group dedicated to high-power

devices) to develop the new epitaxial growth mechanism Transmorphic Heteroepitaxy for producing next-

generation GaN-on-SiC power devices (‘Transmorphic Epitaxial Growth of AlN Nucleation Layers on SiC

Substrates for High-Breakdown Thin GaN Transistors’, Applied Physics Letters, vol115, no22, 25 November

2019).

Specifically, SweGaN collaborated with the scientists in electron microscopy and modeling at Linköping

University and senior researchers at IEMN to explore the nature of the new epitaxial growth mechanism and the

potential of SweGaN’s QuanFINE hybrid GaN–SiC heterostructures for high-power device applications (joining to

the firm’s existing product portfolio for RF components and devices).

“Not only is this a high-impact innovation, but it comes together with a scientific discovery of a novel epitaxial

growth mechanism, which we coin transmorphic,” says the paper’s co-author Lars Hultman, professor at

Linköping University and member of the Royal Swedish Academy of Sciences.

“This breakthrough could significantly reduce the power loss for high-power devices, which would truly manifest

the superiority of GaN power devices over silicon super-junction power devices and silicon carbide MOSFETs for

650V-rated devices,” says chief technology officer Jr-Tai Chen.

The new results show Transmorphic Heteroepitaxy growth where less than 1nm-thick atomic interlayers with

ordered vacancies are created to sufficiently accommodate the lattice mismatch at the interface between the

first epilayer and the substrate.

SweGaN highlights the following features:

• The new growth mechanism suppresses the formation of structural defects in the beginning of the

epitaxy, which enables grain-boundary-free aluminium nitride (AlN) nucleation layers and subsequent

high-quality buffer-free GaN-based heterostructures to be realized on SiC substrates.

• A GaN high-electron-mobility transistor (HEMT) heterostructure with a total thickness of less than

300nm grown by the transmorphic epitaxial scheme on a semi-insulating SiC substrate shows a lateral

critical breakdown field of ~2MV/cm and a vertical breakdown voltage of ≥3kV (measured by senior

researchers at IEMN).

• The critical breakdown field is nearly three times higher than that of GaN-on-Si epiwafers grown by the

conventional thick-buffer approach. So, the device’s ON-resistance has the potential to be lower by

more than one order of magnitude than the value achievable currently, according to Baliga’s figure of

merit (BFOM).

“With these new results, SweGaN will now extend the focus of its QuanFINE technology to include the global

power market in addition to RF devices, particularly in Asia showing the most hunger for new-generation GaN

power devices,” says Chen. “We anticipate releasing more new findings on the performance of QuanFINE based

power devices in the near future.”

GaNEX | III-N Technology Newsletter No. 83 | 57

FBH-led project ‘power transistors based on AlN (ForMikro-LeitBAN)’ launched SemiconductorToday

Coordinated by the Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH) of Berlin,

Germany, the recently launched joint project ‘power transistors based on AlN (ForMikro-LeitBAN)’ aims to

develop highly efficient power semiconductors that can pave the way for a wide range of novel applications –

from e-mobility to artificial intelligence.

Smart energy supply, electro-mobility, broadband communication systems and applications of artificial

intelligence (AI) are driving constant growth in the number of interacting and interconnected systems. However,

with the growing number of systems and increasing data traffic, primary energy consumption is also rising.

Electrical energy must be converted at all times to be usable by the various systems, which is why the need for

electrical conversion is also increasing. In Europe alone, it is estimated that more than 3TeraWatt-hours of

energy (the amount of electricity produced by a medium-sized coal-fired power plant) are lost by energy

conversion each year. Efficient energy conversion is therefore key for applications like AI and Industry 4.0

(representing the fourth industrial revolution based on digitization processes in manufacturing). The

prerequisite for this are efficiently switching power semiconductors that enable high power density. Used to a

large extent, this would result in noticeable energy savings and make a relevant contribution to CO2 reduction.

The project aims to develop aluminium nitride (AlN) semiconductor material for this task, to test it with suitable

devices and to qualify it for future applications in systems. Until 2023, the project will be funded with €3.3m by

Germany’s Federal Ministry of Education and Research (BMBF) within the program ForMikro (Forschung für

neue Mikroelektronik).

Picture: Gallium nitride amplifier from an earlier FBH project. In the ForMikro-LeitBAN project, the technology

for millimeter waves is to be transferred to aluminum nitride. (© FBH/schurian.com)

Aluminum nitride – starting material with potential

The efficiency of systems is limited by static and dynamic power losses of semiconductors, determined by the

respective material. It is becoming increasingly difficult to increase the efficiency of electrical converters and

power amplifiers with conventional silicon-based power components. New semiconductor materials with

improved properties must therefore be investigated and brought to market maturity, says FBH. The project

partners aim to use aluminum nitride (AlN), which has so far been little studied for electronic applications but

GaNEX | III-N Technology Newsletter No. 83 | 58

offers up to 10,000 times less conduction losses than silicon devices. It is also characterized by very high

breakdown strength and thermal conductivity – ideal prerequisites for power semiconductors with high energy

density and efficiency. Free-standing insulating AlN wafers are to be used and qualified as the substrate.

Compared to AlN epitaxy on foreign substrates such as silicon carbide (SiC), the dislocation density can be

reduced by five orders of magnitude. This offers the potential for fast and efficient switching devices while

maintaining high reliability.

Full process chain – from crystal growth to system demonstrators

From a conceptual point of view, the novel AlN components are based on well-researched GaN technology. A

new aspect is the transition from conventional foreign substrates such as silicon carbide, sapphire or silicon to

free-standing AlN substrates. ForMikro-LeitBAN is researching the development of such AlN wafers and testing

them in a tailor-made device process. Test systems for millimeter-wave applications and for power electronic

energy converters qualify the new highly efficient AlN devices for applications in corresponding systems.

ForMikro-LeitBAN involves the following partners, which collectively span the entire value chain (from AlN

wafers to both millimeter-wave and power electronic systems):

• Ferdinand-Braun-Institut (FBH): AlN device design and development;

• Fraunhofer IISB, Erlangen (IISB): AlN crystal growth, wafer manufacturing;

• TU Bergakademie-Freiberg (IAP): Process module development, analytics;

• Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU): material analysis;

• Brandenburgische Technische Universität Cottbus-Senftenberg (BTU): AlN millimetre-wave systems;

• Technische Universität Berlin (TUB): AlN power electronic systems.

The technology will also be prepared for transfer of into an industrial environment. The consortium’s work is

hence being supported by an industrial advisory board comprising Infineon for power electronics, UMS for

millimetre-wave technology and III/V-Reclaim for the recycling of AlN wafers. A respective follow-up project is

also planned.

Sumitomo Electric to begin 150mm GaN-on-SiC production after ordering Aixtron AIX G5+ MOCVD system SemiconductorToday

Deposition equipment maker Aixtron SE of Herzogenrath, near Aachen, Germany says that Japan’s Sumitomo

Electric Device Innovations Inc (SEDI), a subsidiary of Sumitomo Electric Industries Ltd, has ordered an AIX G5+

metal-organic chemical vapor deposition (MOCVD) system with 8x6-inch wafer configuration (for delivery in

2019) in order to expand its production capacity of gallium nitride-on-silicon carbide (GaN-on-SiC) radio

frequency (RF) devices for wireless applications such as radars, satellite communication and base stations for

the rapidly expanding 5G mobile networks.

SEDI has already been relying on Aixtron’s Showerhead technology for the production of 4-inch GaN high-

electron-mobility transistor (HEMT) epitaxial wafers. The progressive deployment of 5G networks but also the

introduction of new technologies like beamforming is expected to drive a rapid upturn in demand, steering the

adoption of more efficient 6-inch substrates for RF applications on Aixtron’s proven Planetary systems.

The new reactor is equipped with an EpiCurve TT metrology system as well as Auto-Feed Forward and P400 UV

Pyrometer Close Loop temperature control. Aixtron adds that the system’s wafer uniformity and precise process

control is especially important for device production on cost-intensive silicon carbide wafers.

GaNEX | III-N Technology Newsletter No. 83 | 59

Sumitomo Electric Device Innovations Inc has an established portfolio of RF components, including a range of

GaN HEMT devices for radar, mobile phone base stations, and general applications. The GaN-on-SiC HEMT

devices enable high power amplification at operating frequencies of 28-40GHz and beyond, as required by new

5G communication standards.

Navitas’ GaNFast Power ICs used by HYPER in smallest 100W 4-port wall charger SemiconductorToday

Navitas Semiconductor Inc of El Segundo, CA, USA has announced its partnership with California-based HYPER

by Sanho Corporation to introduce the HyperJuice 100W 4-port charger with GaNFast power IC technology to

achieve what is reckoned to be the world’s smallest and lightest portable form-factor.

Founded in 2014, Navitas introduced what it claimed to be the first commercial gallium nitride (GaN) power ICs.

The firm says that its proprietary ‘AllGaN’ process design kit (PDK) monolithically integrates GaN power field-

effect transistors (FETs) with GaN power, analog and logic circuits, enabling faster charging, higher power

density and greater energy savings for mobile, consumer, enterprise, eMobility and new energy markets.

Measuring only 85.3mm x 60.8mm x 28.9mm (150cc), the HyperJuice 100W is powerful enough to charge two

15” Macbooks simultaneously (via the 2x USB-C), with flexibility for two more mobile devices via the additional

two USB-A ports.

“We wanted to make the smallest, most flexible 100W charger ever, so the circuit board and components are

laid out in the most compact and space-efficient manner using only the industry’s most efficient components

that can deliver the best performance,” says Daniel Chin, CEO of HYPER by Sanho Corporation. “GaNFast

technology enables 45% lower energy loss than the old, slow silicon chargers in the market today, and for the

ultimate in portability, at only 208g, it’s 50% lighter than competition too,” he adds.

The HyperJuice 100W uses power-sharing technology to deliver optimal charging to a vast array of multiple

devices, from watches and air-pod chargers all the way to a single 100W for the new Apple 16” Macbook. Either

of the two USB-C outputs can deliver the maximum 100W as specified by the USB Power Delivery (PD)

specification, with the two USB-A sockets providing up to 18W each for lower power, quick-charge or legacy

systems. Capable of worldwide AC voltage input, the HyperJuice is supplied with ‘snap-fit’ AC adapters (UK,

EU/Korea, AU) to support the international explorer and business traveler without additional bulky, heavy

converters.

“As shown by the $1.5m Kickstarter backing, confidence in the 100W HyperJuice is extremely high,” comments

Navitas’ CEO Gene Sheridan.

OPTOELECTRONICS

Indium gallium nitride surface-emitting superluminescent light diodes SemiconductorToday

Ireland’s Tyndall National Institute claims a record high 2.2W for output power from indium gallium nitride

(InGaN) superluminescent light-emitting diodes (SLEDs) [R. Cahill et al, Appl. Phys. Lett., vol115, p171102, 2019].

The researchers used slanted facets to direct the amplified spontaneous emission (ASE) through the GaN

substrate with very low feedback, avoiding laser action. The team also claims that their device is the first

surface-emitting structure, since previous reports used edge-emitting geometries.

GaNEX | III-N Technology Newsletter No. 83 | 60

The team comments: “The surface emitting structure provides potential for integration of further functionality

onto the back side of the device, increasing its potential for fiber-based systems and displays.” Other potential

uses include high-resolution optical coherence tomography, compact image projectors and smart solid-state

lighting.

SLEDs combine the operating principles of LEDs and laser diodes. Lasers generally use Fabry-Perot reflecting

structures to feedback light and boost stimulated emission. SLEDs use stimulated emission in a one-pass

structure to amplify spontaneously generated photons. The light from SLEDs benefits from features such as high

power output and high directionality. A number of strategies are used to suppress feedback, such as absorbing

facets or bent cavities.

Figure 1: Epitaxial structure.

The Tyndall InGaN material heterostructure was grown on n-GaN substrates using metal-organic vapor phase

epitaxy (Figure 1). The fabricated device (Figure 2) consisted of a 3μm-wide waveguide with 1mm gain length.

The etched end facets of the waveguide were angled at 45° to form turning mirrors, directing the emitted

radiation through the substrate. The back-side of the GaN substrate was polished to minimize scattering of the

radiation. A further measure to reduce feedback and increase light extraction was to apply a silicon dioxide anti-

reflective layer to the substrate surface.

Figure 2: Schematic of blue surface-emitting LED.

The device was operated with 220ns pulses and 1% duty cycle (Figure 3). The maximum output power of 2.2W

was achieved at 1.5A injection (50kA/cm2 density). The forward voltage was between 6V and 7V. The external

quantum efficiency at the maximum power was 49%. The peak wavelength occurred at 416nm. The researchers

GaNEX | III-N Technology Newsletter No. 83 | 61

comment: “The devices were not observed to degrade under these conditions, testament to the quality of the

low-defect-density substrate.”

Figure 3: Light–current-voltage and gain characteristics of blue SLED under pulsed operation.

Theoretical analysis using a standard gain model suggested that higher powers could be achieved in future. “The

peak optical powers provided by this device are far higher than has been previously reported,” the team writes.

The group attributes the high power to the technique for avoiding feedback: directing the radiation through the

substrate, rather than using absorbing back facets, for example.

The onset of amplified spontaneous emission occurs for an injection current of about 300mA. At lower current

the full-width at half maximum (FWHM) was around 26nm in wavelength. This decreased to the order of 6nm

(corresponding to a 41meV energy spread) above 300mA. FWHM values for InGaN lasers tend to be less than

1nm.

The anti-reflective coating was found to suppress parasitic lasing. In devices without such coating, evidence of

laser action occurred above 700mA injection.

Analysis of spontaneous emission from the top side of the device suggested active-region heating of the order of

110K between 300mA and 1.5A injection. Also, the study suggested that the carrier temperature increased by

about 100K between threshold and maximum power.

Increasing the pulse duration up to 1500ns reduced the output power (~20%) and increased the peak

wavelength slightly, indicating the effects of junction heating on the device. The researchers hope that improved

thermal management measurements could lead to longer pulse lengths or even continuous-wave operation at

higher currents.

Improving metal-organic growth of aluminium nitride on silicon carbide SemiconductorToday

University of California Santa Barbara (UCSB) in the USA have improved metal-organic chemical vapor

deposition (MOCVD) aluminium nitride (AlN) growth on silicon carbide (SiC) with a view to aluminium gallium

nitride (AlGaN) deep-ultraviolet light-emitting diode (DUV LED) and optoelectronics fabrication [Christian J.

Zollner et al, Appl. Phys. Lett., vol115, p161101, 2019].

GaNEX | III-N Technology Newsletter No. 83 | 62

The work was aimed at providing crack-free AlN templates for AlGaN growth with low threading dislocation

density without using costly and time-consuming approaches such as pulsed lateral overgrowth or growing very

thick (>10μm) buffer layers.

The researchers comment: “Combining overall improvements in AlN MOCVD techniques, improved SiC wafer

quality, and growth-mode control concepts demonstrated in molecular beam epitaxy (MBE), we find that

MOCVD growth of AlN/SiC is a viable route to high-quality UV-LED template layers.”

The team also points out that there are highly selective dry etch techniques for efficient SiC substrate removal,

raising the prospect of high-efficiency deep-UV LED fabrication. Such removal would be necessary for sub-

300nm deep-UV wavelengths that include the UV-C 260nm-285nm range, since SiC is highly absorbing of these

high-energy photons. In fact, SiC becomes absorbing around 380nm. UV-C LEDs could be used to kill bacterial

and viral pathogens in air, water, and on surfaces.

AlN can also be grown on much lower-cost sapphire, which is transparent to deep UV. The advantage of SiC is

that it is a much better match in terms of crystal structure. The researchers also point out that “there is no risk

of inadvertent nitrogen-polar growth on the substrate’s Si-face.”

At present, deep-UV LEDs exhibit low wall-plug efficiency due to a number on factors, one of which is the

presence of threading dislocations that direct electric energy into non-radiative recombination processes.

The UCSB MOCVD used trimethyl-aluminium and ammonia precursors as the sources of the aluminium and

nitrogen, respectively. A 250nm AlN initiation layer was grown at 1200°C, followed by 2.7μm AlN at 1400°C. The

growth rates were 1.5Å/s and 6Å/s, respectively. The two-step process targeted reduced numbers of threading

dislocations and a smoother surface.

Figure 1: Symmetric triple-axis 2ω-θ x-ray diffraction scans of AlN/SiC films, with SiC double-peak (blue) for

reference. Growth sequence with (black) and without (orange) ammonia pretreatment compared up to 75nm,

along with full 2.95μm AlN thickness template (black). Logarithmic intensity scale.

GaNEX | III-N Technology Newsletter No. 83 | 63

The 4H SiC substrates came from two suppliers. The ‘sample A’ substrate was mechanically polished with

polishing marks obscuring the atomic steps typically produced during the crystal growth process. In ‘sample B’,

which had a smoother surface from chemical-mechanical planarization (CMP), these steps were visible in

terraced surface structures. Samples A and B were 250μm and 500μm thick, respectively.

AlN films grown on sample B were found to have reduced tensile stress and less cracking. “The marked

reduction in tension when switching to smooth substrates suggests that small island size is a primary driver of

stress generation on rough substrates,” the team comments.

A 10 minute ammonia pretreatment of sample B at 1400°C for 10 minutes changed the slight tensile stress to

strong compression with a value of -1.1GPa. The surface was also crack-free up to a 5μm scale. X-ray rocking

curves also showed reduced full-width at half-maximum (FWHM) diffraction peaks, suggesting higher film

quality (Figure 1).

One effect of the pretreatment was to increase the spacing of the atomic steps from 165nm to 330nm. The

shorter step distance in the initial surface has been found to increase threading dislocation density and to create

lattice stacking mismatch problems.

Figure 2: In-situ curvature of AlN template on three substrate types: rough SiC with ammonia pretreatment

(top, tensile), smooth substrate (middle, weakly tensile), and smooth substrate with ammonia treatment

(bottom, highly compressive). Growth stress and 20-21 FWHM, Δω, listed. Inset: thermal expansion mismatch

stress: data (gray) compared with literature models (red, dashed) and linear least squares fit (black, solid).

Laser monitoring of the substrate curvature during growth (Figure 2) suggested a thermal expansion coefficient

mismatch in sample B of 1.13x10-6/°C, which resulted in a slight lattice mismatch increase of 0.15% at 1375°C. A

thick AlN layer is fully relaxed at its growth temperature, but on cooling to room temperature develops tensile

stress ~700MPa that can lead to cracking.

Plan-view transmission electron microscopy gave a threading dislocation density value of 2.4x108/cm2.

GaNEX | III-N Technology Newsletter No. 83 | 64

SUEZ and AquiSense partner on UV-C LED water disinfection for point-of-use laboratory applications SemiconductorToday

ikkiso Group company AquiSense Technologies LLC of Erlanger, KY, USA (which designs and manufactures water,

air and surface disinfection systems based on UV-C LEDs) has announced a unique product for SUEZ, which

manufactures water purification solutions for the healthcare, laboratory and scientific research sectors. The

partnership provides SUEZ with AquiSense’s patented ultraviolet light-emitting diode (UV-C LED) water

treatment technology for water disinfection directly at the point of use in critical laboratory applications.

AquiSense and SUEZ have been cooperating for over a year in a joint development effort to deliver a laboratory

water purification unit equipped with UV-C LED technology. The new product offers a high-level microbial

disinfection barrier directly at the point of use. Unlike competing units, where pathogens can enter the

upstream pipeline contaminating the system and future samples, the new UV LED disinfection acts as a barrier

preventing contamination from entering the water purification system as a whole.

“This partnership signifies an adaptation of the UV LED technology in the more critical fields of healthcare and

research,” says AquiSense’s European sales director Thomas Arnold.

“The new system developed by SUEZ eliminates recontamination problems by using LED lamps located within

the dispense head, at the point of use,” says SUEZ’s innovation engineer John Higgs. “This is the first time such

technology has been used in this way and brings a number of further important benefits.”

Plessey develops native red InGaN LEDs on silicon for micro-LED displays SemiconductorToday

Plessey of Plymouth, UK, which develops embedded micro-LED technology for augmented-reality and mixed-

reality (AR/MR) display applications, has developed what it claims is the first gallium nitride on silicon (GaN-on-

Si)-based red LED.

While indium gallium nitride (InGaN)-based blue and green LEDs are commercially available, red LEDs are

typically based on aluminium indium gallium phosphide (AlInGaP) material or color-converted red LEDs. For

augmented-reality applications, achieving high-efficiency ultra-fine-pitch red pixels (<5µm) remains elusive due

to severe edge effects from AlInGaP material and cavity losses from color-conversion processes.

InGaN-based red LEDs offer lower manufacturing costs, scalability to larger 200mm- or 300mm-diameter wafers

and better hot/cold factor over incumbent AlInGaP-based red LEDs. However, achieving red spectral emission

with InGaN material is challenging due to the high indium content inducing significant strain in the active region,

GaNEX | III-N Technology Newsletter No. 83 | 65

subsequently reducing crystal quality and creating numerous defects. Plessey says that it has overcome these

challenges by using a proprietary strain-engineered active region to create an efficient InGaN red LED.

Plessey’s InGaN red micro-LEDs have a wavelength of 630nm at an injection current density of 10A/cm2, a full

width at half maximum (FWHM) of 50nm, hot/cold factor over 90% and higher efficiencies over conventional

AlInGaP and color-converted red LEDs at ultra-fine pixel pitches. With this result, Plessey now has the capability

to manufacture native blue, green and red InGaN material or to tune wavelengths from 400nm to 650nm using

its GaN-on-Si platform.

“It creates a path towards low-cost manufacturing of ultra-fine-pitch and efficient red InGaN pixels, which will

accelerate the adoption of micro-LEDs in both AR micro-displays and mobile/large display applications,” says Dr

Wei Sin Tan, Plessey’s director of Epitaxy and Advanced Product Development.

Other recent milestones from Plessey include what is claimed to be the first wafer-level bonded monolithic

3000ppi (pixel-per-inch) GaN-on-Si micro-LED emissive display hybridized to an active-matrix CMOS backplane,

as well as native blue and green emission layers on the same wafer. Plessey is continuing to rapidly develop

micro-LED display solutions, with its roadmap including the production of full-RGB micro-LED displays in 2020.

Plessey is exhibiting in booth #21861 (South Hall 1) at the 2020 Consumer Electronics Show (CES) in the Las

Vegas Convention Center (7–10 January). The firm is joining forces with Compound Photonics of Vancouver, WA,

USA (a provider of compact high-resolution micro-display technologies for AR/MR applications) to develop what

is reckoned to be the smallest 1080p micro-LED-based near-eye display solution for AR/MR applications.

Demonstrated at CES will be active-matrix displays in both native blue and green; as well as the new direct-drive

display with the first-generation development kit. The technology is being showcased within an head-mounted

display (HMD) head-up display (HUD) projection system.

OTHER

University of Illinois reports thermal conductivity dependence on dislocation density of various GaN materials SemiconductorToday

Gallium nitride (GaN) materials are critical for energy conversion, communications and sensing but, despite

material advantages, existing mainstream GaN photonic and electronic devices are limited by the thermal heat

GaNEX | III-N Technology Newsletter No. 83 | 66

extraction, and one of the biggest challenges in GaN devices (including RF transistors and LEDs) is heat

extraction.

A research team at the University of Illinois at Urbana-Champaign (UIUC) led by professor Can Bayram has now

reported what is clamed to be the first systematic study of the thermal conductivity of gallium nitride materials

with various dislocation densities, including hydride vapor phase epitaxy (HVPE)-grown GaN, high nitride

pressure (HNP)-grown GaN, and metal-organic chemical vapor deposition (MOCVD)-grown GaN on sapphire

(GaN/sapphire) and on silicon (111) (GaN/Si) – see K. Park and C. Bayram, ‘Impact of dislocations on the thermal

conductivity of gallium nitride studied by time-domain thermoreflectance’, J. Appl. Phys. 126, 185103 (2019).

GaN thermal conductivities (κGaN) of HVPE GaN, HNP GaN and MOCVD-grown GaN/sapphire and GaN/Si are

measured as 204.7(±4.6), 206.6(±6.8), 191.5(±10.5) and 164.4(±3.2)W/m.K, respectively, using time-domain

thermoreflectance (TDTR). Dislocation densities (σD) of HVPE GaN, HNP GaN, GaN/sapphire, and GaN/Si are

measured as 4.80(±0.42)x105, 3.81(±0.08)x106, 2.43(±0.20)x108 and 1.10(±0.10)x109cm-2, respectively, using

cathodoluminescence and XRD. Impurity concentrations of Si, H, C and O are measured by secondary-ion mass

spectroscopy (SIMS) to complement the analysis.

Graphic: Effect on thermal conductivity of dislocation density in various GaN materials. κGaN of HVPE GaN,

HNP GaN, GaN/sapphire and GaN/Si as a function of σD (open symbols). Empirical model by Mion et al [Appl.

Phys. Lett. 89, 092123 (2006)], κGaN = 230tanh0.12(5×106/σD) (dotted line), new empirical model, κGaN =

210 tanh0.12(1.5×108/σD) (dashed line, University of Illinois work), and modified Klemens’ model (solid line,

University of Illinois work) are plotted together for comparison.

Using the experimental data, the team proposes a new empirical model to describe how thermal conductivity of

GaN is affected by dislocation density, specifically κGaN = 210tanh0.12(1.5x108/σD). They also propose a

GaNEX | III-N Technology Newsletter No. 83 | 67

modification in Klemens’ model, where dislocation-induced scattering strength is increased, to explain the

experimental rate of decrease in thermal conductivity with increasing dislocation density.

Their empirical expression provides a means to estimate the thermal conductivity of heteroepitaxially grown

GaN samples indirectly by determining the dislocation density which is, in many cases, simpler than directly

measuring the thermal conductivity.

The team reckons that the work provides key design guidelines for the thermal management of GaN-based

devices, typically grown on foreign substrates with high dislocation densities.

Veeco’s revenue rebounds in Q3 as 300mm GaN MOCVD cluster system accepted for pilot production SemiconductorToday

For third-quarter 2019, epitaxial deposition and process equipment maker Veeco Instruments Inc of Plainview,

NY, USA has reported revenue of $109m, down 14% on $126.8m a year ago but up 11.5% on $97.8m last

quarter and above the midpoint of the $95-115m guidance range.

The LED Lighting, Display & Compound Semiconductor segment – which includes photonics, 5G RF, power

devices and advanced display applications – contributed $24m (22% of overall revenue), more than doubling

from just $10m last quarter, including service and upgrades for LED customers and shipment of Veeco’s first

300mm fully automated single-wafer gallium nitride (GaN) metal-organic chemical vapor deposition (MOCVD)

cluster system to a “leading-edge semiconductor fab” for a pilot-production environment (after completing

development during the quarter). “We recently obtained acceptance from our customer on this tool,” notes

CEO Bill Miller.

The Front-End Semiconductor segment (formerly part of the Scientific & Industrial segment, before the May

2017 acquisition of lithography, laser-processing and inspection system maker Ultratech Inc of San Jose, CA,

USA) contributed $34m (31% of total revenue), up 36% on $25m last quarter, driven by shipment of Veeco’s

second production extreme ultraviolet (EUV) mask blank system as well as sales of multiple laser spike annealing

(LSA) systems. Also, shipments to data storage customers remained solid as they continued to invest in

technology and capacity.

The Advanced Packaging, MEMS & RF Filter segment – including lithography and Precision Surface Processing

(PSP) systems sold to integrated device manufacturers (IDMs) and outsourced assembly & test firms (OSATs) for

Advanced Packaging in automotive, memory and other areas – contributed $11m (10% of overall revenue),

falling 31% from $16m last quarter, reflecting continued market softness.

The Scientific & Industrial segment fell back by 15% from $47m last quarter to $40m (37% of total revenue),

including ion beam system shipments to data storage customers as well as sales of ion beam sputtering systems

to high-end optical coating customers.

Read more

GaN substrate market to grow at 10% CAGR to 2027 SemiconductorToday

In terms of revenue, the global gallium nitride (GaN) substrate market will expand at a compound annual growth

rate (CAGR) of ~10% to $225m in 2027, estimates a report by Transparency Market Research.

GaNEX | III-N Technology Newsletter No. 83 | 68

GaN substrates promise to dramatically enhance the performance, efficiency and ubiquity of sophisticated

power management and control functions. If low-cost bulk GaN substrate is not available, GaN can be grown on

other substrates such as sapphire, silicon carbide (SiC) or silicon. For better cost economics, GaN devices can be

fabricated on large-diameter silicon substrates in existing silicon CMOS (complementary metal-oxide-

semiconductor) fabs. GaN devices are gaining popularity due to various advantages that they offer including

high breakdown voltage, high switching speed, high thermal conductivity and low on-resistance. This is expected

to have a positive impact on the gallium nitride substrate market.

GaN substrates have evolved

significantly since their

introduction a few years ago. The

growing use of GaN technology

devices for high-frequency, high-

voltage, and high-temperature

applications is expected to drive

the global GaN substrate market

during the forecast period.

Increasing adoption of white-light

LEDs is another factor boosting the

GaN substrate market. GaN

substrates are increasingly being

used to make white-light LEDs, in

addition to power devices, that

exceed the performance of current

devices, as they offer improved electric characteristics. Furthermore, rapid advances in GaN technology have led

to the development of efficient GaN substrates with low defect density and free macro defect density. Hence,

they can increasingly be used for realizing white-light LEDs. The increasing adoption of white-light LEDs is hence

expected to drive growth of the GaN substrate market.

Asia-Paciffic region to remain dominant

Having accounted for a key share of the global GaN

substrate market in 2018, the Asia-Pacific region is

expected to continue to dominate between 2019

and 2027 due to the rising popularity of GaN

devices for various applications in several end-use

industries. China constituted a significant share of

the Asia-Pacific market in 2018, and the country

will see large investments in R&D, targeted at

innovating new technologies. Also, the region is

home to prominent GaN technology companies

that are engaged in R&D on innovative GaN

solutions and their introduction to the

marketplace.

North America has emerged as the second-largest

market for GaN substrates. The region is expected

to maintain a considerable share of the global

market during the forecast period, due to the

GaNEX | III-N Technology Newsletter No. 83 | 69

increasing adoption of GaN substrates for various applications such as white-light LEDs and the increasing

adoption of electric vehicles. GaN-based devices and GaN substrates can be employed in several applications in

the automotive sector, such as LiDAR, 48V–12V power distribution, and high-intensity headlights. The region

therefore presents significant opportunities for the GaN substrate market, the report reckons.

Europe is expected to be a lucrative market for GaN substrates throughout the forecast period due to the

growing popularity of GaN devices and their rising use in the automotive industry in countries in Western

Europe and Central Europe. The European market is anticipated to increase in the next few years due to rapid

industrialization in the region. Furthermore, key players are engaged in making technical advances in GaN

technology to overcome the challenges associated with devices based on this technology.

Key players in the global GaN substrate market are displaying synergies through close cooperation and

collaboration in sales, marketing and technical advances. GaN substrate suppliers are also expanding by forming

strategic alliances with peers as well as various research institutions in order to establish themselves as players

in the global market.

Boost to magnesium doping of gallium nitride on freestanding substrates SemiconductorToday

Japan’s National Institute for Materials Science (NIMS) has found that magnesium doping of gallium nitride

(GaN:Mg) is far more effective in material grown homoepitaxially on freestanding substrates as opposed to

GaN/sapphire templates [Liwen Sang et al, Appl. Phys. Lett., vol115, p172103, 2019].

The researchers point to the reduction of self-compensation as the basis for the enhanced doping performance.

Self-compensation occurs where acceptor states are neutralized by the generation of parasitic deep-donor non-

radiative recombination centers (NRCs). Also, the reduced numbers of threading dislocations in material grown

on freestanding substrates is thought to reduce Mg diffusion effects that adversely affect doping performance.

Freestanding substrates can have threading dislocation densities as low as 104/cm2, some three orders of

magnitude lower than for GaN/sapphire templates. Of course, freestanding substrates are significantly more

expensive than the templates, but the development of potential application opportunities and substrate

production technology should encourage economies of scale in future.

The enhanced GaN:Mg on freestanding substrates was found to have five to ten times the free hole density,

implying higher conductivity. In addition, one would expect higher mobility if lower magnesium concentration

can be used due to reduced impurity scattering.

Another potential use of p-GaN is as a current-blocking layer in vertical metal-oxide-semiconductor field-effect

transistors (MOSFETs) and current-aperture vertical electron transistors (CAVETs). The creation of p-GaN:Mg

during epitaxial growth is preferred over ion implantation. The latter process suffers from excessive out-

diffusion of the dopants during thermal anneal processes.

Metal-organic chemical vapor deposition (MOCVD) was used to grown 1μm Mg-doped GaN on c-plane n+-GaN

freestanding substrates with 4x106/cm2 threading dislocation density. The growth temperature was 1000°C and

bis(methylcyclopentadienyl) magnesium was the precursor for the doping. The Mg-doped layer was grown on

an undoped 2μm GaN buffer with 5x1015/cm3 free electron density. The Mg doping was activated with 30-

minute annealing at 725-820°C.

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One effect of using GaN substrates was narrow peaks in x-ray diffraction (XRD) rocking curves (Figure 1):

68arcsec full-width at half maximum (FWHM) for the (002) plane and 95arcsec for (102). These values

correspond to a threading dislocation density of 7x106/cm2. The same growth process, but using GaN/sapphire

templates, led to FWHM values of 280arcsec and 491arcsec for the (002) and (102) planes, respectively. The

estimated threading dislocation density in this case was 6x109/cm2, almost three orders of magnitude higher

than for the GaN:Mg on freestanding substrate.

Figure 1: (left) XRD omega rocking curves of (002)- and (102)-plane reflection for homoepitaxial and

heteroepitaxial GaN:Mg films. (right) Free hole concentration and [Mg] values for homoepitaxial and

heteroepitaxial GaN:Mg films.

Hall measurements with lightly doped GaN on GaN/sapphire template with 1.4x1019/cm3 {Mg} concentration

gave a 6x1016/cm2 free hole density. Homoepitaxy on freestanding GaN increased the free hole concentration

five-fold to 3x1017/cm3 with a reduced {Mg} of 8x1018/cm3. The higher Mg incorporation on sapphire was

attributed to a higher density of edge-type dislocations.

Heavier Mg-doping resulted in free hole concentrations of 6.0x1017/cm3 on freestanding substrate (1.8x1019

Mg concentration). This was ten times the 6.1x1016/cm3 on sapphire for the same Mg flow. The team

comments: “The marked enhancement of the doping efficiency is attributed to the suppression of the Mg-

related self-compensation centers or non-radiative recombination centers benefitting from the greatly reduced

dislocation density.”

The researchers also found that the relation between photoluminescence (PL) spectral structure and p-type

conductivity in GaN:Mg was different on freestanding GaN substrates, compared with heteroepitaxy on

sapphire (Figure 2).

With heteroepitaxial GaN:Mg a blue-band luminescence (BL, ~2.9eV) is associated with onset of p-conductivity.

This luminescence is generally attributed to deep donor-acceptor pair (DAP) recombination.

By contrast the NIMS researchers found that ultraviolet luminescence (UVL, ~3.26eV) was the signal for

homoepitaxial GaN:Mg on freestanding GaN to be p-type conducting. These emissions were attributed to free

electron or shallow donor recombination with acceptor levels.

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The PL spectra also include near-band-edge (NBE) emissions and yellow luminescence (YL). The YL emissions are

attributed to electron transitions into deep acceptor levels associated with carbon atoms on nitrogen sites.

Figure 2: PL spectra of p-GaN films grown on (a) GaN substrates and (b) GaN/sapphire templates activated at

725°C in N2 with different Mg doping concentrations. (c) and (d) PL spectra of homoepitaxial and

heteroepitaxial GaN:Mg films activated at varying temperatures, respectively.

The homoepitaxial GaN:Mg had increased ultraviolet luminescence with increased activation anneal

temperatures up to 750°C, but then BL emissions started appearing, indicating reduced effectiveness. The

higher activation temperatures also resulted in increased surface roughness measured using atomic force

microscopy: 0.81nm root mean square at 770°C, compared with 0.25nm at 725°C.

The NIMS team comments: “The rough morphology deteriorates the luminescence behaviors, which is related

to the increased thermal emission of electrons from donor levels to the conduction band and their recapture by

the non-radiative recombination centers on the rougher surface. The electrical current of Ohmic contacts is

reduced when the activation temperature is higher than 750°C.”

X-ray photoelectron spectra (XPS) indicated that homoepitaxy also improved the uniformity of surface states,

avoiding regions with excess Mg-Ga-O. Such excess Mg-Ga-O inhibits abrupt interfaces when growing aluminium

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oxide dielectric. Abrupt interfaces are desired for metal-oxide-semiconductor structures in vertical field-effect

transistors with high mobility and stable positive threshold voltages.

Electrochemical membrane release for aluminium gallium nitride devices SemiconductorToday

Researchers in Sweden and Germany have been developing electrochemical etching as a means to create thin-

film aluminium gallium nitride (AlGaN) optoelectronic and power-electronic devices [Michael A. Bergmann et al,

Appl. Phys. Lett., vol115, p182103 2019]. AlGaN alloys are wide-bandgap materials with the potential for deep

ultraviolet (UV) light emission and for electronics that can sustain high electric fields and voltages before

breakdown.

The researchers at Sweden’s Chalmers University of Technology, Germany’s Technische Universität Berlin and

Sweden’s KTH Royal Institute of Technology comment: “Heterogeneously integrated AlGaN epitaxial layers will

be essential for future optical and electrical devices like thin-film flip-chip ultraviolet light-emitting diodes, UV

vertical-cavity surface-emitting lasers, and high-electron-mobility transistors on efficient heat sinks. Such AlGaN

membranes will also enable flexible and micromechanical devices.”

Releasing the AlGaN layers from the epitaxial growth substrate would enable vertical cavities with dielectric

applied to both sides of a membrane. For high-power electronics, thin-film formats would allow better thermal

management by applying the active semiconductor layers directly to heatsinks. However, present methods for

releasing AlGaN such as laser lift-off tend to damage the material, reducing performance in the final device.

Figure 1: (a) AlGaN sample structure, (b) three-electrode setup for electrochemical etching, and (c) etching

current versus time for etching Al0.11Ga0.89N sacrificial layer at 30V.

The researchers first grew a 2x1018/cm3 silicon-doped Al0.5Ga0.5N layer on c-plane sapphire with an AlN

template layer using a close-coupled showerhead metal-organic chemical vapor deposition (MOCVD) reactor

(Figure 1). The n-type conductivity from the silicon doping ensured current spreading for uniform

electrochemical etching.

The current-spreading layer was followed by a 225nm 0.5x1018/cm3 {Si] lightly doped Al0.5Ga0.5N etch-stop

layer. The sacrificial layer for membrane release was 130nm 2x1019/cm3 heavily Si-doped AlxGa1-xN. The

membrane layer was 580nm (1900nm for Al0.11Ga0.89N sacrificial layer sample) unintentionally doped

Al0.5Ga0.5N.

X-ray analysis showed that the Al0.5Ga0.5:Si was ‘pseudomorphic’ - i.e. strained – on all sacrificial layer

compositions.

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The electrochemical etching was enabled by dry reactive-ion etching 10μm-diameter via holes in a 7x9 400μm

pitch array to expose the sacrificial layer. The etched holes reached down to the current-spreading layer. The

electrochemical contact with the current-spreading layer was made through an electron-beam evaporated and

annealed vanadium/aluminium/vanadium/gold metal stack. The top-side of the membrane was protected from

etching damage with a 1.3μm photoresist layer.

The electrochemical etch used three electrodes in 0.3M nitric acid electrolyte, which was constantly stirred with

a magnetic bar. The AlGaN ‘working electrode’ was kept at a constant positive potential relative to the

silver/silver chloride (Ag/AgCl) ‘reference electrode’. Control of the process was through a graphite rod ‘counter

electrode’, which allowed the current flow to vary in the low milliamp range. The samples were 5mmx10mm.

The electrochemical etch was found to proceed isotropically around the etch holes, creating an air gap between

the substrate and membrane. Eventually the etch fronts merge. With an Al0.5Ga0.5N sacrificial layer, an etch

potential of 30V resulted in smooth surfaces on the upper and lower etch-stop layers. At the lower potential of

25V some residues were left on the etch-stop layers. Even lower potentials, of 20V and 15V, resulted in

increasingly porous sacrificial layers.

Figure 2: (a) As-grown MQW sample structure, (b) transferred MQW-containing structure, (c) PL spectrum of

as-grown MQW probed from Ga-polar side and transferred structure probed from etched N-polar side, and

(d) time-resolved PL of structures.

The researchers attribute the etching to the generation of holes at AlGaN/electrolyte interface from Zener

tunneling or avalanche breakdown in a depletion region. “These holes oxidize AlGaN at the interface, and the

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oxidized material can be dissolved by the electrolyte,” the team explains. The researchers propose a chemical

reaction equation:

2AlxGa1-xN + 6h+ → 2xAl3+ + 2(1-x)Ga3+ + N2

Atomic force microscopy on the etched surface of a membrane transferred to a silicon carrier had 3.5nm root-

mean-square (RMS) roughness on a 1μmx1μm area. The sacrificial layer used for the electrochemical etch was

Al0.27Ga0.73N.

A multiple quantum well (MQW) structure was grown on a 130nm Al0.37Ga0.63N sacrificial layer to show that

the electrochemical etch could be used without affecting device performance (Figure 2). The 2x1018/cm3 {Si]

Al0.5Ga0.5N 4μm-thick underlayer was relaxed. The sacrificial layer aluminium content was chosen to be

transparent for photoluminescence (PL) analysis but low enough to contrast with the surrounding layers.

The MQWs were indium aluminium gallium nitride with 21% Al content. The three wells were 2nm thick,

separated by 5nm Al0.3Ga0.7 barriers. The magnesium-doped p-type layers were an Al0.75Ga0.25N electron-

blocking layer, an AlGaN superlattice (SL), and a 20nm p-GaN cap.

The material was prepared for electrochemical etching by dry reactive-ion etching circular mesas. Palladium was

deposited on the p-GaN cap. The mesas were partially covered with 1μm sputtered silicon dioxide (SiO2) to

prevent parasitic etching during the electrochemical process. Finally, a titanium/gold bond pad was deposited

on the palladium.

The electrochemical etch potential was 25V. The released structures were transferred to silicon carriers with

titanium/gold bonding layer using a 300°C thermos-compression process.

The PL analysis showed a small red-shift after transfer. The researchers report “This shift of 2nm could be

caused by small local variations in the Al-composition and thickness over the sample, residual strain in the

epitaxy, and process-induced strain.”

Time-resolved measurements before and after transfer showed the same PL decay rate of 340ps. The team

concludes: “This confirms that the electrochemical etching and transfer process do not influence the quality of

the QWs and, hence, are an appropriate process for fabrication of devices based on free-standing membranes.”

Panasonic to sell its chip unit to Taiwan's Nuvoton for $250 million Reuters

TOKYO (Reuters) - Panasonic Corp (6752.T) said it would sell its loss-making semiconductor unit to Taiwan’s

Nuvoton Technology Corp (4919.TW) for $250 million as the Japanese electronics giant struggles to lift its profit

amid a lack of growth drivers.

The sale is part of Panasonic’s plans to cut fixed costs by 100 billion yen ($920 million) by the year ending in

March 2022 by consolidating production sites and overhauling loss-making businesses.

Panasonic has already divested most of its chip business as it lost to more nimble Korean and Taiwanese rivals,

and has shut down or shifted its manufacturing facilities to its joint venture (JV) with Israel’s Tower

Semiconductor (TSEM.TA).

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Its semiconductor unit currently focuses on designing power-management chips and sensors for smartphones,

cars and security cameras. It sold part of the power management chip business to Japan’s Rohm Co (6963.T) this

month.

The latest deal includes the sale of the entire JV, which is owned 51% by Tower and 49% by the Panasonic chip

unit. The JV operates three Japanese chipmaking facilities.

Panasonic said the sale will not have any significant impact on its earnings. The value of the deal that Panasonic

has announced excludes the amount Nuvoton would pay for Tower Semiconductor’s stake in the joint venture.

Nuvoton said in a statement the all-cash transaction was expected to close by June 2020, and would “increase

Nuvoton’s presence in the global semiconductor industry through greater scale and volume of semiconductor

solutions”.

Nuvoton, which was spun off from Winbond Electronics Corp (2344.TW) in 2008, supplies chips for electronic

devices including computers and audio products.

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PATENT APPLICATIONS

More than 290+ new patent families (inventions) were published in November 2019.

Other patent applicants Asahi Kasei, Chip Foundation Technology, East China Normal University, Exagan, Fujian Prima Optoelectronics, Guangdong Institute of Semiconductor Industrial Technology, Guangdong University of Technology, HC Semitek, Institute of Semiconductors, Jiangsu Ji Cai Intelligent Sensing Technology Research Institute, Julicheng Semiconductor, Meijo University, Nanjing University of Science & Technology, Nuodinghan Intelligent Electrification Research Institute, Osram Opto Semiconductors, Purdue Research Foundation, Qualcomm, Seoul Viosys, Shandong Inspur Huaguang Optoelectronics, Shanghai Huali Microelectronics, Shenzhen Jing Xiang Technologies, Sun Yat Sen University, Suzhou Institute of Nano Technology & Nano Bionics Chinese Academy of Sciences, Suzhou Institute of Nano Technology & Nano Bionics Sinano Chinese Academy of Sciences, Taiwan Semiconductor Manufacturing, University of Colorado, University South Science & Technology China, Wuhan University, Wuhu Qidi Semiconductor, Xi An Keruisheng Innovative Technology, Xiamen Changelight, 3D Floor No 6 Industrial Six Road Pingzhen Industrial Zone Taoyuan City China, ABB Schweiz, Ames Micron, Analog Foundries, Ascatron, Beijing Bozhong Yiyou Technology, Black Peak, Cambridge Enterprise, Cas Spectra Technology, Central South University, Changshaniumidrivetechnologyco, Chunghwa Precision Test Technology, Columbia University, Dalian University of Technology, Delta Electronic Enterprise Management, Dongguan Institute of Opto Electronics Peking University, Ecole Polytechnique Federale De Lausanne (EPFL), Elux, Enkris Semiconductor, Ericsson, ETRA Semiconductor, First Affiliated Hospital of Medical College of Xi An Jiaotong University, Foshan Guoxing Semiconductor Technology, Fuji Electric, General Interface Solution, GIS Technology, Gree Electric Appliances, Guangdong APT Electronics, Guangdong Electronic Information Engineering Research Institute of UESTC, Guangdong Fenghua Advanced Technology Holding, Guangdong Fenghua Core Power Technology, Guangdong Juhua Printed Display Technology, Guangwei Integration Technology, Guangxi Subtropical Crops Research Institute, Gwangju Institute of Science & Technology, Haidike Photoelectric Science & Technology, Harbin Institute of Technology, Hebei Yongsheng Foodstuff, Hengshan Jiacheng New Material, Hosei University, Huaiyin Teachers College, Huangshan Ruixing Automobile Electronic System, Hyperfine Research, Imec;

GaNEX | III-N Technology Newsletter No. 83 | 77

Notable new patent applications

Enhancement-mode high-electron-mobility transistor Publication Number: WO2019/224448 Patent Applicant: EXAGAN

The invention relates to an enhancement-mode high-electron-mobility transistor comprising: • a structure (10) including a stack (1) made of III-V semiconductor materials defining an interface (2) and capable of forming a conduction layer (3) in the form of a two-dimensional electron-gas layer; • a source electrode (20) and a drain electrode (30) forming an electrical contact with the conduction layer (3); and • a gate electrode (40) arranged on top of the structure (10), between the source electrode (20) and the drain electrode (30). The structure (10) comprises a bar (4) that is arranged below the gate electrode (40) and passes through the interface (2) of the stack (1). Said bar (4) comprises two semiconductor portions exhibiting opposite types of doping, defining a p-n junction in proximity to the interface (2).

Micro light-emitting diode display fabrication and assembly Publication Number: US20190363069, WO2019/226255 Patent Applicant: INTEL

Micro light-emitting diode (LED) displays, and fabrication and assembly of micro LED displays, are described. In an example, a pixel element for a micro-light emitting diode (LED) display panel includes a blue color nanowire or nanopyramid LED above a first nucleation layer above a substrate, the blue color nanowire or nanopyramid LED including a first GaN core. A green color nanowire or nanopyramid LED is above a second nucleation layer above the substrate, the green color nanowire or nanopyramid LED including a second GaN core. A red color nanowire or nanopyramid LED is above a third nucleation layer above the substrate, the red color nanowire or nanopyramid LED including a GaInP core.

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Pixel architectures for low power micro light-emitting diode displays Publication Number: WO2019/226246 Patent Applicant: INTEL

Pixel architectures for low power micro light-emitting diode displays are described. In an example, a micro light emitting diode pixel structure includes a substrate having a plurality of conductive interconnect structures in a first dielectric layer thereon. A plurality of micro light emitting diode devices is in a second dielectric layer above the first dielectric layer, individual ones of the plurality of micro light emitting diode devices electrically coupled to a corresponding one of the plurality of conductive interconnect structures. The plurality of micro light emitting diode devices includes an orange micro light emitting diode device, a green micro light emitting diode device, and a blue micro light emitting diode device. A transparent conducting oxide layer is disposed on the plurality of micro light emitting diode devices and on the second dielectric layer.

Photonic and electronic devices on a common layer Publication Number: WO2019/217141 Patent Applicant: RAYTHEON

Photonic devices having A11-xScxN and A1yGa1-yN materials, where A1 is Aluminum, Sc is Scandium, Ga is Gallium, and N is Nitrogen and where 0 is less than x and x is less than or equal to 0.45 and 0 is less than or equal to y and y is less than or equal to 1.

Method of dividing a bar of one or more devices Publication Number: WO2019/222669

Patent Applicant: UNIVERSITY OF CALIFORNIA

A method for dividing a bar of one or more devices. The bar is comprised of island-like III-nitride-based semiconductor layers grown on a substrate using a growth restrict mask; the island-like III-nitride-based semiconductor layers are removed from the substrate using an Epitaxial Lateral Overgrowth (ELO) method; and then the bar is divided into the one or more devices using a cleaving method.

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Gallium-nitride-based transcaps for millimeter wave applications Publication Number: WO2019/226330, US20190363198 Patent Applicant: QUALCOMM

Certain aspects of the present disclosure provide a semiconductor variable capacitor. The semiconductor variable capacitor generally includes a first semiconductor region having a first doping type, a second semiconductor region having a second doping type different from the first doping type, a third semiconductor region disposed between the first semiconductor region and the second semiconductor region, a first terminal disposed adjacent to the first semiconductor region, a second terminal disposed adjacent to the second semiconductor region, and a third terminal disposed above the third semiconductor region. The first semiconductor region, the second semiconductor region, and/or the third semiconductor region include gallium nitride. The third semiconductor region includes multiple semiconductor layers having different materials. A capacitance between the first terminal and the third terminal is configured to be adjusted by varying a control voltage applied to at least one of the first terminal or the second terminal.

Enhanced doping efficiency of ultrawide bandgap semiconductors by metal-semiconductor assisted epitaxy Publication Number: WO2019/227100, US20190363218 Patent Applicant: UNIVERSITY OF MICHIGAN

An epitaxial growth process, referred to as metal-semiconductor junction assisted epitaxy, of ultrawide bandgap aluminum gallium nitride (AIGaN) is disclosed. The epitaxy of AIGaN is performed in metal-rich (e.g., Ga-rich) conditions using plasma- assisted molecular beam epitaxy. The excess Ga layer leads to the formation of a metal-semiconductor junction during the epitaxy of magnesium (Mg)-doped AIGaN, which pins the Fermi level away from the valence band at the growth front. The Fermi level position is decoupled from Mg-dopant incorporation; that is, the surface band bending allows the formation of a nearly n-type growth front despite p-type dopant incorporation. With controlled tuning of the Fermi level by an in-situ metal- semiconductor junction during epitaxy, efficient p-type conduction can be achieved for large bandgap AIGaN.

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Implanted dopant activation for wide bandgap semiconductor electronics Publication Number: US20190341261, WO2019/213001 Patent Applicant: US NAVY

An enhanced symmetric multicycle rapid thermal annealing process for removing defects and activating implanted dopant impurities in a Ill-nitride semiconductor sample. A sample is placed in an enclosure and heated to a temperature T1 under an applied pressure P1 for a time t1. While the heating of the sample is maintained, the sample is subjected to a series of rapid laser irradiations under an applied pressure P2 and a baseline temperature T2. Each of the laser irradiations heats the sample to a temperature Tmax above its thermodynamic stability limit. After a predetermined number of temperature pulses or a predetermined period of time, the laser irradiations are stopped and the sample is brought to a temperature T3 and held at T3 for a time t3 to complete the annealing.

Formation of a III-N semiconductor structure Publication Number: US20190362967 Patent Applicant: IMEC

According to an aspect of the present disclosure, there is provided a III-N semiconductor structure comprising: a semiconductor-on-insulator substrate; a buffer structure comprising a superlattice including at least a first superlattice block and a second superlattice block formed on the first superlattice block, the first superlattice block including a repetitive sequence of first superlattice units, each first superlattice unit including a stack of layers of AlGaN, wherein adjacent layers of the stack have different aluminum content, the second superlattice block including a repetitive sequence of second superlattice units, each second superlattice unit including a stack of layers of AlGaN, wherein adjacent layers of the stack have different aluminum content, wherein an average aluminum content of the second superlattice block is greater than an average aluminum content of the first superlattice block; and a III-N semiconductor channel layer arranged on the buffer structure.

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Method for fabricating a hybrid display using inorganic micro light emitting diodes (uleds) and organic leds (oleds) Publication Number: US20190355708 Patent Applicant: ELUX A hybrid light emitting diode (LED) display and fabrication method are provided. The method forms a stack of thin-film layers overlying a top surface of a substrate. The stack includes an LED control matrix and a plurality of pixels. Each pixel is made up of a first subpixel enabled using an inorganic micro LED (uLED), a second subpixel enabled using an organic LED (OLED), and a third subpixel enabled using an OLED. The first subpixel emits a blue color light, the second subpixel emits a red color light, and the third subpixel emits a green color light. In one aspect, the stack includes a plurality of wells in a top surface of the stack, populated by the LEDs. The uLEDs may be configured vertical structures with top and bottom electrical contacts, or surface mount top surface contacts. The uLEDs may also include posts for fluidic assembly orientation.

Nitride semiconductor light emitting element Publication Number: JP2019197857, CN110473943, US20190348569, EP3567643 Patent Applicant: PANASONIC A flip-chip light emitting diode element capable of reducing lateral resistance. The flip-chip light emitting diode element includes a stacked body structure configured by sequentially stacking a first n-type group III nitride semiconductor layer having a carrier concentration that is at least 1 × 1019cm-3but less than 3 × 1020cm-3, a second n-type group III nitride semiconductor layer having a carrier concentration that is at least 5 × 1017cm-3but less than 1 × 1019cm-3, a light-emitting layer formed by a group III nitride semiconductor, and a p-type group III nitride semiconductor layer. A height of unevenness on an interface between the first n-type group III nitride semiconductor layer and the second n-type group III nitride semiconductor layer is greater than that of unevenness of an interface between the second n-type group III nitride semiconductor layer and the light emitting layer.

Semiconductor element and method for manufacturing the same Publication Number: US20190355580, JP2019201158 Patent Applicant: TOSHIBA

According to one embodiment, a semiconductor element includes a first nitride semiconductor region, a second nitride semiconductor region, and an intermediate region provided between the first nitride semiconductor region and the second nitride semiconductor region. A Si concentration in the intermediate region is not less than 1×1018/cm3 and not more than 1×1019/cm3. A charge density in the intermediate region is 3×1017/cm3 or less.

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Electronic device including an enhancement-mode hemt and a method of using the same Publication Number: DE102018111319, JP2019197894, US20190348568, CN110474230 Patent Applicant: OSRAM

An optoelectronic semiconductor device and a method for manufacturing an optoelectronic semiconductor device are disclosed. In an embodiment an optoelectronic semiconductor device includes a semiconductor body comprising a first region of a first conductive type, an active region, a second region of a second conductive type and a coupling-out surface, wherein the first region, the active region and the second region are arranged along a stacking direction, wherein the active region extends from a rear surface opposite the coupling-out surface to the coupling-out surface along a longitudinal direction transverse to or perpendicular to the stacking direction, wherein the coupling-out surface is arranged plane-parallel to the rear surface, and wherein the coupling-out surface and the rear surface of the semiconductor body are produced by an etching process.

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