InAs Inserted Channel HEMT

2003-21667MDCL

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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

1. Advantage for use in low noise and high frequency device

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

3. 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)a) As Lg decreases, an appropriate aspect ratio has to be maintained to alleviate sho

rt channel Effect.b) Also, Channel thickness has to be reduced for proper aspect ratio (∵ The thinning

of barrier layer is limited by current tunneling)c) Disadvantage ( Reducing of sheet carrier density in a channel and Undesired scatte

ring phenomena because of hetero-junction interface and the enhancement of ionized dopant in supply layer)

InAs Inserted Channel HEMT

Conventional InP HEMT vs InAs Inserted HEMT (Ref. 1)

Cap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48As

Cap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48As

Barrier I In0.52Al0.48As Barrier I In0.52Al0.48As

Spacer i In0.52Al0.48As Spacer i In0.52Al0.48As

Channel i InxGa1-xAsChannel i InxGa1-xAs

Channel i InxGa1-xAsChannel i InAs

Buffer i In0.52Al0.48As Buffer i In0.52Al0.48As

InP Substrate InP Substrate

Delta-doping

Conventional InP HEMT InAs Inserted HEMT

Carrier Transport Characteristic (Ref. 6)

a) Modified Composite Channel b) Conventional InGaAs HEMT c) Conventional Composite chanel HEMT

High Indium Composition Layer

Mobility (cm2/Vs) Sheet Carrier density (cm-2)

Carrier Confinement

In0.8Ga0.2As/InAs/In0.8Ga0.2As

18300 1.9e12 92%

In0.8Ga0.2As 16200 1.6e12 74%

InAs 16000 1.9e12 61%

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 InGaA

s layer High field channel region => The energy of the electrons increases and more and more electrons p

opulate 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 hi

gh-field transport properties, especially the saturation velocity, are better in InP

Physics Band Structure Calculation and Electron Transport (Ref.2)

Γ-valley mass of strained InAs (parallel<Perpendicular) => The strain brings about an increase of the InAs band gap of 0.12eV

InGaAs (x=0.53)

Strained InAs InAs

E(l-Γ) (eV) 0.72 0.84 0.98

E(Γ-X)(eV) 1.06 1.04 1.39

m ＊ (Γ) 0.042 0.037(//), 0.04( ㅗ )

0.033

ml ＊ (L) 1.18 0.647 3.57

mt*(L) 0.11 0.135(t1)0.091(t2)

0.12

ml ＊ (X) 0.49 0.926 1.32

mt*(X) 0.23 0.296(t1)0.150(t2)

0.28

α(Γ)(eV-1) 0.806 0.858 1.188

α(Γ)(eV-1) 0.896 0.09 0.075

α(Γ)(eV-1) 0.068 0.06 0.0198

a(A) 5.87 5.87(//) 6.054

Physics Monte Carlo Simulation Include polar optical phonon scattering and inter-valley deformation potential

scattering at 300K

26% enhancement

16% enhancement

In0.53GA0.47As Unstrained InAs Strained InAs

Mobility (cm2/Vs) 13000 17800 16400

Peak Drift Velocity (m/s)

3.1e7 3.65e7 3.65e7

The reduction of slopeWide Γ-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 test’s result is Z=3nm and Lw=4nm (Consideration of Carrier Modulation and Sho

rt Channel Effect) => 13000cm2/Vs

II. The Design of Subchannel The Thickness of InAs Inserted HEMT (Another Test) (Ref. 4) Double Sided Delta-doping 을 이용 (for low output conductance and kink-free I/V C

haracteristic)

a) The Enhancement of the electron transport propertyb) 47% electron mobility improvement 40% the effective electron velocity increment (@ 300K)

II. The Design of Subchannel Design 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/In0.52Al0.48As

Barrier I In0.52Al0.48As Barrier I In0.52Al0.48As

Spacer i In0.52Al0.48As Spacer i In0.52Al0.48As

Channel i In0.53Ga0.47As

Channel i InAs

Buffer i In0.52Al0.48As

InP Substrate InP Substrate

Buffer i In0.52Al0.48As

Channel i InAsChannel i In0.3Ga0.7AsChannel i

In0.7Ga0.3As

Channel i In0.53Ga0.47As

Channel i In0.53Ga0.47As

Channel i In0.53Ga0.47As

Channel i In0.7Ga0.3As Channel i In0.3Ga0.7As

Compressively strained channelStructure A

Tensilely strained channelStructure B

17% population increment10% gm increment8% ft increment(A: 220 GHz B:238 GHz @0.1um Lg)

II. The Design of Subchannel AlAs/InAs Superlattice Structure (Channel Composition Modula

tion Transistor) (Ref. 7)a) For high electron sheet carrier density and good carrier confinement and high electro

n transportb) To improve the thermal stability of InP HEMT

a) Epi-Structure b) 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 voltageb) InAs 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 HEMT The enhancement of mobility characteristic The scattering cased by ionized donor and interface roughness

Low effective mass and high mobility in Inverted HEMT

IV. 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-Structure b) Band Structure

IV. AlSb/InAs HEMT Lattice 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 개선방안

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 c

onfinement (In0.8Ga0.2As/InAs/In0.8Ga0.2As channel) ∵ 3.5 % InAs mismatch in the channel

II. 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 HEMT Reference1. 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 InAsHori, 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 channelAkazaki, 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. Böhm, D. Xu, H. Heiß, S. Kraus, G. Tränkle and G. Weimann

5. Impact of subchannel design on DC and RF performance of 0.1 μm MODFETs with InAs-inserted channelXu, 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/V·s InAlAs/InGaAs pseudomorphic structure by channel indium composition modulationNakayama, T.; Miyamoto, H.; Oishi, E.; Samoto, N.;Indium Phosphide and Related Materials, 1995. Conference Proceedings., Seventh International Conference on , 9-13 May 1995 Pages:733 - 736

InAs Inserted Channel HEMT7. InAlAs/InGaAs channel composition modulated transistors with InAs channel and AlAs/InAs superlattice barrier layer

Onda, K.; Fujihara, A.; Wakejima, A.; Mizuki, E.; Nakayama, T.; Miyamoto, H.; Ando, Y.; Kanamori, M.; Electron Device Letters, IEEE , Volume: 19 , Issue: 8 , Aug. 1998 Pages:300 - 302

8. Improving the characteristic of an InAlAs/InGaAs Inverted HEMT by inserting an InAs layer into the InGaAs channel Solid State Electronics vol. 38 NO. 5 pp997-1000 1995 Tatsushi Akazaki, Tatamoto Enoki, Kunihiro Arai and Yasunobu Ishi 9. 0.1um AlSb/InAs HEMTs with InAs subchannel Electronics Letters 23rd July 1998 Vol. 34 No.15 J.B boos, M.J. Yang, B.R. Bennett, D. Park, W. Kruppa, C.H. Yang and R. Bass

10. InAs channel HFETs: current status and future trends Bolognesi, C.R.; Signals, Systems, and Electronics, 1998. ISSSE 98. 1998 URSI International Symposium on , 29 Sept.-2 Oct. 1998 Pages:56 - 61