Electronic structures and photoemission spectroscopy

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:

Semimetallic InAs/GaSb structures are known to contain simultaneously both two dimensional electrons in the InAs and two dimensional holes in the GaSb layers. Following successful anodisation of undoped GaSb, we describe transport measurements performed on a wide area gated sample and also a single quantum point contact. In the large area gated sample, the electron density increases and the hole density decreases when a positive gate voltage is applied. Under negative bias, an additional layer of holes is created at the interface between the insulating and GaSb capping layers, which is confirmed by self-consistent modelling of the band profile under external bias. The conductance of the point contact is found to exhibit quantised values. PACS: 72.20My, 23.80Ey, 73.40Qv. © 1994 Academic Press. All rights reserved.

Abstract:

Low-field negative magnetoresistance has been studied on Ga+ ion focused-ion-beam-patterned GaAs/Ga1-xAlxAs heterojunctions as a function of carrier density and temperature. The negative magnetoresistance (NMR) is very large at low densities and decreases with increasing carrier density, giving a magnetoconductance linear in T at low densities but closer to a lnT dependence at higher values. The NMR of this grid structure is well explained using weak localization modified by boundary scattering in an array of one-dimensional point contacts. The NMR disappears after illumination as the patterning is screened by the increased electron density. From this model, we fit the phase-breaking rate as 1/τφ=A+BT, where the constant term is attributed to boundary scattering and the linear temperature dependence arises from electron-electron scattering. © 1993 The American Physical Society.