ABCs: InAs/AlSb HEMT development

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AlSb/InAs/InAsP/AlSb Composite-Channel HFETs
Heng-kuang Lin
C. Kadow, J.-U. Bae, M. Dahlstrom, M. Rodwell,
A. C. Gossard University of California, Santa
Barbara G. Nagy, J. Bergman, B. Brar, G.
Sullivan Rockwell Scientific, Thousand Oaks, Ca
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AlSb/InAs/AlSb HFETs

• Disadvantages
• Small Eg (InAs) low Vbr
• High kink current, high Ig
• Degraded noise performance

• Advantages
• High m , vsat
• ft , fmax 162 GHz
• ( Lg 0.25 mm )
  

J. Bergman, et al., IPRM, 2003.
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Our Approach for Breakdown Composite Channel

• Motivation
• ABCS HFETs need higher
• Vbr.
• Approach Composite channel
• Electrons move in high-
• mobility material at low
• fields ? InAs.
• Electrons move in high-Vbr , high-vsat material
  at high
• fields
• ? What material ?

High field region
Low field region

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Why InAsP as subchannel ?

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Characterization of Composite Channel - I
First step Characterize InAs channels
InAs / InAsP 2 DEG
Energy band diagram / Carrier profile
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Characterization of Composite Channel - II
R-T Hall Ns vs P ratio
R-T Hall Mobility vs P ratio

• 430 ºC Optimal InAsP growth temperature
• m gt 20,000 cm2/ V-s for P ratios up to 0.4

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Characterization of Composite Channel - III
Second step Characterize InAsP subchannels
Energy band diagram / Carrier profile
R-T Hall Mobility Ns vs P ratio
?
X

• 430 ºC is again optimal InAsP growth
  temperature
• m gt 7,000 cm2/ V-s in InAs0.8P0.2 subchannels

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Carrier Transfer vs Impact Ionization
e
1.
Vgs
2.
y direction
y
x
h
?
?
x direction
1. Transfers to InAsP 2. Impact-ionizes
Wave functions
e
Ey2.1X105 V/cm
Ey2. 3X105 V/cm
?EEg(InAs)
Ec(InAsP)
e
h
Ec(InAsP)
Ec(InAs)
Ec(InAs)
InAs
InAsP
Surface
substrate
Ev(InAs)
Ev(InAsP)
Ey, max, transfer 2.2X105 V/cm
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Our Approach Introduction of a Doping Dipole
Dipole P-doping (Be) plus N-doping
(Te)

• Advantages
• Reduced external bias to
• reach Ey, max, transfer
• Easier electron transfer
• Improve breakdown
• 2. Hole barrier in buffer
• Prevents hole accumulation
• Reduces kink current

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Suggested Composite-Channel Device Layer
Structure
As-grown material m 14,500 cm2/ V-s (R-T
Hall) Ns1.7x1012
cm-2
3.5 strain
Si 1x1019 cm-3
1.5x1012 cm-2
InSb-like interfaces
InAs Channel 10 nm
InAsP Subchannel 10 nm
Digital alloy 20 P
0.9x1012 cm-2
7 strain, dislocations, buffer

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Standard Processing Flow
1) Ohmic contacts
1)
2)
2) Mesa isolation by dry etch
TLM Rsh 220 ?/square Rc 0.065 ?-mm
3) Optical recessed gate
4)
3)
4) Metal 1

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Comparison between Single and Composite Channel
DC Characteristics - I
HFETs 0.7x40 ?m2 Blue composite channel Red
single channel
No impact ionization peaks
gds (Red) gds (Blue) 14 1 ( Vgs - 0.2 V,
Vds 0.6 V )
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Comparison between Single and Composite Channel
DC Characteristics - II
HFETs 0.7x40 ?m2 Blue composite channel Red
single channel
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RF Performance for Composite Channel
Max fT for single channel
Max fT for composite channel

• fT Lg 32 GHz-µm composite channel
• fT Lg 44 GHz-µm single channel

Slight degradation on RF performance
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Conclusion
Growth - Develop materials for InAs/InAsP
composite-channel HFETs ? (InAs) gt 20,000
cm2/ V-s for 40P in InAsP subchannels Device
performance DC - Increased Vbr (0.5V to
0.8V) - Reduced kink currents ( gds 141) -
Suppressed impact ionization in Ig RF -
fT,max 46 GHz, fmax,max 61 GHz (0.7-µm gate)
- fT Lg degrades from 44 to 32 GHz-µm
InAs/InAsP composite-channel HFETs are
a promising enhancement to InAs
single-channel HFETs.