Investigation of new devices and characterization techniques in the III-V semiconductor system

by Cheng, Xiao-chang

Abstract (Summary)
This thesis concerns the investigation of novel devices and material characterization techniques in the III-V semiconductor system. In the first part of the thesis, we demonstrate that novel devices, such as avalanche photodiodes and tunnel switch diodes, can be fabricated from InAs/GaSb/A1Sb heterostructures by molecular beam epitaxy (MBE). In the second part of the thesis, ballistic electron emission microscopy (BEEM) is employed to examine the local band offset in these heterostructures, which is often found to be crucial in device design. In the avalanche photodiode study, devices with near infrared response out to 1.74 [mu]m were demonstrated. Two types of devices were investigated: those with a bulk Al0.04Ga0.96Sb multiplication region and those with a GaSb/A1Sb superlattice multiplication region. Both types of devices were implemented in a MBE grown p[superscript -]n[superscript +] structure that uses a selectively doped InAs/AlSb superlattice as the n-type layer. This particular structure was optimized through several design, fabrication, characterization cycles. It was found that the photodiode dark current depended critically on the InAs/A1Sb superlattice period and the resulting band offset at the p[superscript -]n[superscript +] heterojunction. The InAs/AlSb superlattice was henceforth optimized by using a three stage design. The ionization rates in bulk multiplication layer devices were measured and found to be consistent with hole impact ionization enhancement in Al0.04Ga0.96Sb. However, direct comparison with superlattice multiplication layer devices revealed the latter to be more promising due to more effective dark current suppression from the larger band gap of the superlattice multiplication layer. The second device studied is the tunnel switch diode. We have fabricated the first such device in the antimonide material system and obtained characteristic "S" shaped I-V curves from these devices. The epilayer and barrier dependence of tunnel diode switching were studied and found to deviate significantly from the punch-through model of operation. In addition, the device I-V curve was observed to "hop" between two branches when subjected to high levels of stress. We speculate that this was due to instability associated with mobile charges in the A1Sb tunnel barrier. A computer model was used to simulate the device behavior and generated results consistent with the observed dependence of switching on tunnel barrier thickness. In the second part of the thesis, III-V heterostructures were characterized by using ballistic electron emission microscopy (BEEM). BEEM images were shown to reveal sub surface features in AlxGal-xAs. epilayers, whereas BEEM spectroscopy was used to map out the shift in [capital gamma], X, and L band edges with material composition in AlxGal-xAs. BEEM spectroscopy was also applied to device relevant antimonide heterostructures such as A1Sb barriers and InAs/AlSb superlattices. It was found that electron transport in A1Sb was dictated by the conduction band minium near the X point, and there is large local variation in the AlSb Schottky barrier height. These results were in good correlation with the observed barrier characteristics of A1Sb. Due to the small bandgap of InAs/A1Sb superlattice and the associated high level of noise current, only the shortest period superlattice was examined by BEEM. The resulting band offset agreed with the calculated value and demonstrated that BEEM spectroscopy can be applied to structures with a large number of hetero-interfaces.
Bibliographical Information:

Advisor:T. C. McGill

School:California Institute of Technology

School Location:USA - California

Source Type:Master's Thesis

Keywords:applied physics


Date of Publication:05/04/1999

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