Download InAs Inserted HEMT

InAs Inserted Channel HEMT
2003-21667
MDCL
이종원
Contents
I. 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)
b)
c)
d)
their low-field mobility
higher-lying satellite valleys
deeper quantum well depth
higher overshoot velocity
II. Scaling Factor (for sub 0.1um device)
a)
b)
c)
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 HEMT
 Conventional InP HEMT vs InAs Inserted HEMT (Ref. 1)
Cap n In0.53Ga0.47As
n In0.53Ga0.47As/In0.52Al0.48As
Barrier
I In0.52Al0.48As
Spacer
i In0.52Al0.48As
Channel
i InxGa1-xAs
Buffer
i In0.52Al0.48As
InP Substrate
Conventional InP HEMT
Cap n In0.53Ga0.47As
n In0.53Ga0.47As/In0.52Al0.48As
Delta-doping
Barrier
I In0.52Al0.48As
Spacer
i In0.52Al0.48As
Channel
i InxGa1-xAs
Channel
Channel
i InAs
i InxGa1-xAs
Buffer
i In0.52Al0.48As
InP Substrate
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/In
0.8Ga0.2As
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
InGaAs layer
 High 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
Physics
 Band Structure Calculation and Electron Transport (Ref.2)


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
Γ-valley mass of strained InAs (parallel<Perpendicular)
=> The strain brings about an increase of the InAs band gap of 0.12eV
Physics

Monte Carlo Simulation

Include polar optical phonon scattering and inter-valley deformation potential scattering
at 300K
In0.53GA0.47As
Unstrained InAs
Strained InAs
Mobility (cm2/Vs)
13000
17800
16400
Peak Drift Velocity
(m/s)
3.1e7
3.65e7
3.65e7
26% enhancement
16% enhancement
The reduction of slope
Wide Γ-L band separation in InAs
=L enhancement of electron heating
Over 7kV/cm
Electron 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 Short Channel Effect) => 13000cm2/Vs
II. The Design of Subchannel
 The Thickness of InAs Inserted HEMT (Another Test) (Ref. 4)

Double Sided Delta-doping을 이용 (for low output conductance and kink-free
I/V Characteristic)
a) The Enhancement of the electron transport property
b) 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
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
Channel
i In0.52Al0.48As
i In0.53Ga0.47As
Spacer
Channel
i In0.52Al0.48As
i In0.53Ga0.47As
Channel
Channel
Channel
Channel
i
i
i
i
Channel
Channel
Channel
Channel
i
i
i
i
Buffer
i In0.52Al0.48As
Buffer
i In0.52Al0.48As
In0.7Ga0.3As
InAs
In0.7Ga0.3As
In0.53Ga0.47As
InP Substrate
Compressively strained channel
Structure A
--- Structure A
Structure B
In0.3Ga0.7As
InAs
In0.3Ga0.7As
In0.53Ga0.47As
InP Substrate
Tensilely strained channel
Structure B
17% population increment
10% gm increment
8% ft increment
(A: 220 GHz B:238 GHz @0.1um Lg)
II. The Design of Subchannel
 AlAs/InAs Superlattice Structure (Channel Composition
Modulation Transistor) (Ref. 7)
a)
b)
For high electron sheet carrier density and good carrier confinement and high
electron transport
To improve the thermal stability of InP HEMT
a) Epi-Structure
-0.12eV ->-0.17eV
20% improvement of
electron confinement
b) Band Structure
0.2um T-Gate
Mobility 18300 cm2/Vs
ft=180GHz
gm = 1370 ms/mm
III. Normal VS Inverted HEMT
(Ref. 8)
a)
b)
C)
Normal InAs Inserted Channel HEMT : high output conductance and low breakdown
voltage
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)
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)
b)
For high speed and low bias application
(∵ high electron mobility and velocity, high sheet charge density and good carrier
confinement)
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)
6.1A lattice constant
AlSb/InAs conduction band discontinuity 1.35eV
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.
IV. AlSb/InAs HEMT
 개선방안
a. Need a good buffer for good surface morphology and good carrier
transport characteristic
b. Thin InAs channel thickness
Conclusion
I.
a.
b.
Design of Subchannel Band
InAs thickness for high speed and carrier confinement
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
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
 Reference
1.
2.
Modern Microwave Transistors theory, Design, and performance
Frank Schwierz Juin J. Liou
Wiley-Interscience
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. 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 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/V·s InAlAs/InGaAs pseudomorphic structure by channel indium composition
modulation
Nakayama, T.; Miyamoto, H.; Oishi, E.; Samoto, N.;
Indium Phosphide and Related Materials, 1995. Conference Proceedings., Seventh International Conference on , 913 May 1995
Pages:733 - 736
InAs Inserted Channel HEMT
7.
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