Reduction of the unintentional background electron
density in AlSb/InAs/AlSb quantum wells
C. Kadow1, H.-K. Lin1, M. Dahlstrom1, M. Rodwell1,
A.C. Gossard1, B. Brar2, G. Sullivan2
1ECE
Dept., University of California, Santa Barbara
2Rockwell Scientific, Thousand Oaks
Funded by DARPA:
Antimonide-based compound semiconductors (ABCS)
AlSb/InAs/AlSb quantum wells
• High room-temperature mobility of 30,000 cm2/Vs.
• High conduction band offset of 1.3 eV.
Good channel for high-frequency HFETs.
BUT: Intrinsic electron
density is 1x1012 cm-2
mainly due to the surface
pinning position.
EF
Control of the channel
charge is essential for the
HFET threshold voltage and
other device parameters.
Nguyen, C. et. al. APL 60, 1854 (1992)
Experiment: Sample structures
75 A
GaSb
200 A
AlSb
130 A
InAs
300 A
AlSb
AlSb-based
metamorphic buffer
GaAs substrate
Be delta-doping sheet
[Be] = 0 to 1.5 x 1012 cm-2
EF
-
1.4 10
12
1.2 10
12
Undoped
-2
Electron concentration [cm ]
Hall data: Electron density
12
1 10
[Be] = 0.25 x 10
12
cm
-2
11
8 10
[Be] = 0.5 x 10
12
cm
-2
[Be] = 1.0 x 10
12
cm
-2
12
cm
11
6 10
11
4 10
[Be] = 1.3 x 10
11
2 10
[Be] = 1.5 x 10
0
10
100
Temperature [K]
12
cm
-2
-2
Hall data: Electron mobility
Undoped
10
10
12
cm
-2
5
2
Electron mobility [cm / Vs]
[Be] = 0.25 x 10
[Be] = 0.5 x 10
12
cm
-2
[Be] = 1.0 x 10
12
cm
-2
4
[Be] = 1.3 x 10
12
cm
-2
10
[Be] = 1.5 x 10
100
Temperature [K]
12
cm
-2
Variations due to cool-down cycle and
sample-to-sample non-uniformity
12
-2
1.5 10
12
1 10
12
10
4
Blue: Sample #1
Gray: Sample #2
11
2
5 10
-2
1000
0
10
100
T [K]
Mobility [cm / Vs]
Density [cm ]
Be modulation doped InAs well; [Be] = 1.3x10 cm
Control of channel charge
0.8
0.4
Fit:
12
-2
n = 1.06x10 cm - 0.56 N
Be
0
0.4
0.8
Be density [10
•
-2
cm ]
T = 300 K
0.8
0.4
Fit:
12
-2
n = 1.26x10 cm - 0.72 N
Be
0
0
•
•
1.2
12
T = 10 K
Electron density [10
Electron density [10
12
-2
cm ]
1.2
1.2
12
-2
cm ]
1.6
0
0.4
0.8
Be density [10
1.2
12
1.6
-2
cm ]
Linear relationship between Be doping and channel charge.
Slopes are different at T = 10 K and T = 300 K, probably due
to different sources of charge (surface and interfaces).
Carrier freeze-out does not fit linear relationship.
Scattering mechanisms
2
T = 10 K
Electron mobility [cm /Vsec]
6
2
Electron mobility [cm /Vsec]
10
10
5
10
4
Fit:  = 2.45 x 10
10
-31
3
0.2
0.4
0.6 0.8 1
Electron density [10
12
n
3
T = 300 K
30000
10000
8000
Fit:  = 2.35 x 10 n
-2
6000
0.1
-2
cm ]
Electron density [10
1/2
1
12
-2
cm ]
Effects of Be modulation doping:
1. Increased ionized impurity scattering.
2. Reduce Fermi wavevector kF
• Phonon scattering (room temperature).
• Interface roughness scattering (low temperature).
Conclusions and summary
• Demonstrated Be-doping as an effective tool to
reduce the unintentional electron density in InAs
quantum wells.
• Channel charge varies linearly with Be doping.
• Hall measurements show the dependence of the
electron mobility on Be doping, electron density
and temperature.
Future work:
• Quantify scattering mechanisms.
• Application to HFETs.