Robin Nicholas

Abstract:

A new class of insulating and passivating layers on gallium antimonide has been prepared by means of an electrochemical process. In previous work we used this new process of fabrication of passivating and insulating layers for gating devices made from GaSb/InAs/GaSb nanostructures (Chen Y et al 1994 Superlatt. Microstruct. 15 41 and Chen Y 1995 PhD Thesis Hertford College, Oxford, UK). In this publication we describe the effects of the electrochemical process leading to an improvement of the photoluminescence (PL) after the growth of the passivating layer on GaSb. The PL measurements on <100>, <111A> and <111B> GaSb substrates and on GaSb epilayers grown by MOVPE on GaAs indicate significant improvement of the PL intensity even after 12 months. Similar results have been observed on InGaSb/GaSb superlattice structures.

Abstract:

InAs/GaSb strained layer superlattices have been grown by atmospheric pressure MOVPE and the growth conditions optimised by observing, in real time, the in-situ UV absorption of the alkyls in the growth chamber. The Raman scattering of folded longitudinal acoustic phonons in the superlattices has been used as a probe of the periodicity of the superlattice. Atomic force microscopy has also been used to give information about the final surface morphology and RMS roughness of the superlattices. By combining all three techniques, optimum conditions have been found for the growth of short period InAs/GaSb superlattices. These have been used to sandwich a long period superlattice designed for transport measurements. The use of the short period superlattices eliminated additional conducting layers at each end of the semimetallic superlattice and produced structures where the hole and electron densities are equal. Such structures exhibit a dramatic new quantum transport effect where the Hall resistance goes to zero at high pressures and low temperatures.

Abstract:

A correlation between substrate dopant type and the absorption spectra of MQW structures has been identified. Optical absorption spectra from MQW structures grown on S-doped InP can show poorly resolved excitonic features with respect to those obtained from structures grown on both Sn- and Fe-doped substrates. It is proposed that this degradation is due to enhanced interfacial diffusion on the Group V sublattice for structures grown on substrates incorporating low defect densities.