Studies of zinc telluride/indium arsenide/aluminum antimonide heterojunction field-effect transistors and related structures
Abstract
ZnTe/InAs, a II-VI/III-V heterovalent system, is explored in this thesis. The molecular beam epitaxy (MBE) growth of InAs epilayers on InP substrates is established for the first time. Based on the previous results in the studies of the ZnSe/GaAs heterointerfaces, the ZnTe/InAs metal-insulator-semiconductor (MIS) capacitors are grown and characterized. It is found that the change of the surface stoichiometry of InAs before the nucleation of ZnTe yields limited control on the density of interface states; difference in the capacitance-voltage characteristics are observed even though the carriers near the ZnTe/InAs heterointerfaces can not be completely depleted. The ZnTe/InAs/AlSb heterojunction field-effect transistors (HFET) are grown by MBE on semi-insulating InP substrates. Different schemes are used in the preparation of the ZnTe/InAs heterointerfaces. Quantum Hall effect (QHE) is observed in one of the samples with the insertion of two monolayers of AlSb between ZnTe and InAs. Transistor operation at room temperature is observed from the same sample; maximum transconductance measured from a 3-$\mu$m device is around 25 mS/mm. The absence of transistor operation from the direct ZnTe/InAs-interface HFETs motivates us in the exploration of the heterovalent interfaces on the substrates with different orientations. It is speculated that different crystal orientations have different surface cation/anion bonding ratios, which might be an alternative way in achieving the control of the surface stoichiometry. The ZnTe/InAs/AlSb HFETs are grown successfully on (100), (211)B, (311)B, and (110)6$\sp\circ \to$ (111)A substrates. Preliminary results suggest that the use of the less polar orientations indeed reduce the density of interface states; room temperature operation of the direct ZnTe/InAs interface HFETs are observed for the first time from samples with (211)B, (311)B, and (110)6$\sp\circ \to$ (111)A surfaces. This is the first experimental evidence that the electrical properties associated with a heterovalent interface can be controlled by using substrates with different orientations. Nitrogen doping of ZnTe epilayers is studied for the potential application in yellow-green light emitters, as well as contact layers for the ZnSe-based blue light emitters. A hole concentration of nearing 1 $\times$ 10$\sp{19}$ cm$\sp{-3}$ is achieved with the use of a nitrogen plasma source. A novel p-ZnTe/n-AlSb heterojunction diode is also explored.
Degree
Ph.D.
Advisors
Gunshor, Purdue University.
Subject Area
Electrical engineering
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