Robin Nicholas

Abstract:

We have studied magnetotransport in a coupled electron-hole system in an InAs/GaSb heterostructure with two-dimensional periodic potential modulations of different strengths. Strong oscillations in low magnetic field longitudinal magnetoresistance have been observed. The amplitude of these oscillations is a function of the magnetic field applied parallel to the two-dimensional system, which modifies the coupling between the electrons and holes.

Abstract:

Electron transport in InAs/GaSb superlattices under intense parallel electric and magnetic fields is investigated. At low electric fields we observe a conduction threshold, which exhibits magnetic field and temperature dependence. At higher biases the superlattice exhibits a large magneto-resistance and in the quantum limit we observe conduction peaks, which satisfy the Stark-Cyclotron-Resonance condition. Eight band k.p calculations show that the miniband width in this system is strongly k dependent.

Abstract:

We report studies of vertical superlattice transport in short period superlattices at high magnetic fields. This shows new magnetophonon resonances can occur in which LO phonons are resonantly scattered between high density of states regions of the superlattice leading to cycling of the carriers through high conductivity regions of the miniband.

Abstract:

We discuss the use of fixed wavelength infrared absorption measurements as a means for observing compositional changes in MOVPE process gas mixtures using relatively simple instrumentation consisting of an incandescent lamp, a narrow bandpass filter matched to the CH stretch modes of the alkyl precursors, and an infrared detector. An advantage of this setup is that the low energy of the infrared radiation does not induce photolysis reactions on the analyser cell windows in contrast to ultraviolet-based techniques. We present preliminary data on gas composition measurements obtained in the alkyl lines of an MOVPE reactor and show that useful information can readily be obtained on absolute gas concentrations, gas switching transients, and reactor line memory effects. (C) 2000 Elsevier Science B.V. All rights reserved.