Transport properties of InAs/(A1Sb)/GaSb/(A1Sb)/InAs heterostructure systems

by Ma, Pui-wai

(Uncorrected OCR) Abstract of thesis entitled TRANSPORT PROPERTIES OF In As/ (AlSb) /GaSb/ (AlSb) /In As HETEROSTRUCTURE SYSTEMS submitted by Ma Pui Wai for the Degree of Master of Philosophy at The University of Hong Kong in August 2004 In this study, the dynamical conductance of InAs/GaSb/InAs and InAs/AlSb/ GaSb/AlSb/InAs heterostructure systems were calculated within the two-band k-P model, using the general current-conserving theory developed by Biittiker for ac transport and the scattering-matrix approach. These interband systems feature an energy window AE within which the transmission coefficient is nonzero. When the frequency of external bias is comparable to this energy window, the real part of the dynamical conductance shows a series of plateaus which are well correlated with the profile of the transmission coefficient. The number and position of the plateaus can be varied by changing the frequency. At a frequency much smaller than AE1, the phase of the dynamical conductance was well described by the emittance. As the frequency was increased, the capacitive-like and inductive-like behavior observed at off-resonance and on-resonance respectively were enhanced. The conductance and current-voltage curve of a normal-superconducting(NS) junction were also calculated, with normal side being InAs/(AlSb)/GaSb/(AlSb)/ InAs systems. If the energy is far from EF ?A, the conductance resembles the transmission coefficient. In the region of energy just around Ep ?A, the conductance shows two extra peaks, whose heights and positions depend on the relative resonance state. In a symmetric InAs/(AlSb)/GaSb/(AlSb)/InAs system, if there is a resonance state sitting right on the Fermi energy, the conductance shows a high peak with value approaching two. However, in an asymmetric InAs/(AlSb)/GaSb/(AlSb)/InAs system, the conductance shows two sharp peaks or a small peak (depending on the thicknesses of the AlSb layers). For current, compared to a normal system, it shows extra valleys and peaks which can be explained by the conductance behavior.