InAs Inserted Channel HEMT

InAs Inserted Channel HEMT2003-21667MDCL

ContentsI. Introduction

II. The Design of Subchannel of InAs

III. Normal VS Inverted HEMT

IV. AlSb/InAs HEMT Growth on S.I. GaAs

Overview of InGaAs HEMT

Advantage for use in low noise and high frequency device

their high electron mobility & high sheet carrier density & high saturation drift velocity if the InAlAs/InGaAs 2DEG system

Conventional InP HEMT structure : high contact and gate electrode can cause large parasitic source and drain resistances (by the large conductance band discontinuity between the InGaAs cap layer and InAlAs layer, forming a barrier in the current flow between these layers)

I. Introduction

Why?I. Superior to GaAs or InGaAs channel devices a) their low-field mobilityb) higher-lying satellite valleysc) deeper quantum well depthd) higher overshoot velocity

II. Scaling Factor (for sub 0.1um device)As Lg decreases, an appropriate aspect ratio has to be maintained to alleviate short channel Effect.Also, Channel thickness has to be reduced for proper aspect ratio ( The thinning of barrier layer is limited by current tunneling)Disadvantage ( Reducing of sheet carrier density in a channel and Undesired scattering phenomena because of hetero-junction interface and the enhancement of ionized dopant in supply layer)

InAs Inserted Channel HEMTConventional InP HEMT vs InAs Inserted HEMT (Ref. 1)Cap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48AsCap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48AsBarrier I In0.52Al0.48AsBarrier I In0.52Al0.48AsSpacer i In0.52Al0.48AsSpacer i In0.52Al0.48AsChannel i InxGa1-xAsChannel i InxGa1-xAsChannel i InxGa1-xAsChannel i InAsBuffer i In0.52Al0.48AsBuffer i In0.52Al0.48AsInP SubstrateInP Substrate Delta-dopingConventional InP HEMTInAs Inserted HEMT

Carrier Transport Characteristic(Ref. 6)a) Modified Composite Channelb) Conventional InGaAs HEMTc) Conventional Composite chanel HEMT

High Indium Composition LayerMobility (cm2/Vs)Sheet Carrier density (cm-2)Carrier ConfinementIn0.8Ga0.2As/InAs/In0.8Ga0.2As183001.9e1292%In0.8Ga0.2As162001.6e1274%InAs160001.9e1261%

Issue of the InAs Inserted HEMT

I. The Design of Subchannel of InAs for composite channel (dependence of a) Temperature & Thickness b) Enhancement of carrier transport )

II. The Normal and Inverted HEMT Structure

III. AlSb/InAs HEMT (The Growth on S.I GaAs )

Physics

The Basic Idea of Composite Channel

Low field channel region => electrons are mostly located in the high-mobility, small bandgap InGaAs layerHigh field channel region => The energy of the electrons increases and more and more electrons populate the InP layer => Because of the larger bandgap, the rate of impact ionization in InP is smaller compared to that in the InGaAs channel => While the low-field mobility of InP is smaller than that of InGaAs, the high-field transport properties, especially the saturation velocity, are better in InP

PhysicsBand Structure Calculation and Electron Transport (Ref.2)

-valley mass of strained InAs (parallel The strain brings about an increase of the InAs band gap of 0.12eV

PhysicsMonte Carlo SimulationInclude polar optical phonon scattering and inter-valley deformation potential scattering at 300K

26% enhancement

16% enhancementThe reduction of slopeWide -L band separation in InAs =L enhancement of electron heating

Over 7kV/cmElectron energy of strained InAs> unstrained InAs=> Smaller effective mass L & X valley of strained InAs => Higher energy

II. The Design of Subchannel (Ref.3) a) Mobility tested the function of Z and Lw b) This tests result is Z=3nm and Lw=4nm (Consideration of Carrier Modulation and Short Channel Effect) => 13000cm2/Vs

II. The Design of SubchannelThe Thickness of InAs Inserted HEMT (Another Test) (Ref. 4)Double Sided Delta-doping (for low output conductance and kink-free I/V Characteristic)a) The Enhancement of the electron transport propertyb) 47% electron mobility improvement 40% the effective electron velocity increment (@ 300K)

II. The Design of SubchannelDesign Issue (Ref.5)3.5% lattice mismatch of InAs on InP--- Structure A Structure BCap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48AsCap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48AsBarrier I In0.52Al0.48AsBarrier I In0.52Al0.48AsSpacer i In0.52Al0.48AsSpacer i In0.52Al0.48AsChannel i In0.53Ga0.47AsChannel i InAsBuffer i In0.52Al0.48AsInP SubstrateInP SubstrateBuffer i In0.52Al0.48AsChannel i InAsChannel i In0.3Ga0.7AsChannel i In0.7Ga0.3AsChannel i In0.53Ga0.47AsChannel i In0.53Ga0.47AsChannel i In0.53Ga0.47AsChannel i In0.7Ga0.3AsChannel i In0.3Ga0.7AsCompressively strained channelStructure ATensilely strained channelStructure B17% population increment10% gm increment8% ft increment(A: 220 GHz B:238 GHz @0.1um Lg)

II. The Design of SubchannelAlAs/InAs Superlattice Structure (Channel Composition Modulation Transistor) (Ref. 7)For high electron sheet carrier density and good carrier confinement and high electron transportTo improve the thermal stability of InP HEMT

a) Epi-Structureb) Band Structure-0.12eV ->-0.17eV20% improvement of electron confinement

0.2um T-GateMobility 18300 cm2/Vsft=180GHz gm = 1370 ms/mm

III. Normal VS Inverted HEMT(Ref. 8)a) Normal InAs Inserted Channel HEMT : high output conductance and low breakdown voltageInAs Inserted Channel Inverted HEMT : channel layer located on the carrier supply layer => low output conductance ( superior to electron confinement and smaller distance between gate and channel)C) Little kink-effect and a high breakdown voltage

III. Normal VS Inverted HEMTThe enhancement of mobility characteristic The scattering cased by ionized donor and interface roughness

Low effective mass and high mobility in Inverted HEMT

AlSb/InAs HEMT (ref. 9)a) For high speed and low bias application ( high electron mobility and velocity, high sheet charge density and good carrier confinement)b) Disadvantage : charge control problem associated with impact ionization in the InAs channel (will increase as the Lg is reduced due to the higher fields present) a) Epi-Structureb) Band Structure

IV. AlSb/InAs HEMTLattice Matched System (Ref. 10)

I. Current Status 1. Epitaxial Growth Buffer (interface roughness scattering)

2. Impact Ionization Effect a) dominant for short gate-length when the drain bias exceeds the energy bandgap in the channel => Thinner channel scheme (kink effect and low output conductance, transconductance and peak current density) need for trade-off of channel thickness and device performance.

6.1A lattice constantAlSb/InAs conduction band discontinuity 1.35eV

IV. AlSb/InAs HEMT

a. Need a good buffer for good surface morphology and good carrier transport characteristic

b. Thin InAs channel thickness

ConclusionI. Design of Subchannel Band a. InAs thickness for high speed and carrier confinement b. for better performance high sheet carrier density and mobility and carrier confinement (In0.8Ga0.2As/InAs/In0.8Ga0.2As channel) 3.5 % InAs mismatch in the channel

For Low kink effect and high breakdown voltage and the improvement of carrier mobility and sheet carrier density => Inverted HEMT

III. For low cost and similar bandgap engineering compared with InP HEMT => AlSb/InAs HEMT

InAs Inserted HEMTReference1. Modern Microwave Transistors theory, Design, and performance Frank Schwierz Juin J. Liou Wiley-Interscience

2. First principles band structure calculation and electron transport for strained InAs Hori, Y.; Miyamoto, Y.; Ando, Y.; Sugino, O.; Indium Phosphide and Related Materials, 1998 International Conference on ,11-15 May 1998 Pages:104 - 107 3. Improved InAlAs/InGaAs HEMT characteristics by inserting an InAs layer into the InGaAs channel Akazaki, T.; Arai, K.; Enoki, T.; Ishii, Y.; Electron Device Letters, IEEE ,Volume: 13 ,Issue: 6 ,June 1992 Pages:325 - 327 4. MBE growth of double-sided doped InAlAs/InGaAs HEMTs with an InAs layer inserted in the channel ARTICLE Journal of Crystal Growth, Volumes 175-176, Part 2, 1 May 1997, Pages 915-918 M. Sexl, G. Bhm, D. Xu, H. Hei, S. Kraus, G. Trnkle and G. Weimann 5. Impact of subchannel design on DC and RF performance of 0.1 m MODFETs with InAs-inserted channel Xu, D.; Osaka, J.; Suemitsu, T.; Umeda, Y.; Yamane, Y.; Ishii, Y.; Electronics Letters ,Volume: 34 ,Issue: 20 ,1 Oct. 1998 Pages:1976 - 1977 6. High electron mobility 18,300 cm2/Vs InAlAs/InGaAs pseudomorphic structure by ch