1. 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)

2. 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.
Control of the channel charge is essential for the HFET threshold voltage and other device parameters. EF
Nguyen, C. et. al. APL 60, 1854 (1992)

3. Experiment: Sample structures
AlSb
GaSb
InAs
AlSb-based
metamorphic buffer
GaAs substrate
75 A
200 A
130 A
300 A
Be delta-doping sheet
[Be] = 0 to 1.5 x 1012 cm-2 EF -

4. Hall data: Electron density

5. Hall data: Electron mobility

6. Variations due to cool-down cycle and sample-to-sample non-uniformity

7. Control of channel charge
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.

8. Scattering mechanisms
Effects of Be modulation doping:
Increased ionized impurity scattering.
Reduce Fermi wavevector kF
Phonon scattering (room temperature).
Interface roughness scattering (low temperature).

9. 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.