Robin Nicholas

Abstract:

The effective mass has been studied in a series of semiconducting and semimetallic InAs/GaSb superlattices as a function of superlattice period and band gap. The mass is found to be determined almost entirely by the superlattice period, and is relatively insensitive to both the ratio of the InAs to GaSb thickness, and the structure of the interface layer, which was grown as both a monolayer of InSb and GaAs. Using pulsed magnetic fields of up to 180 T it was possible to observe spin-split cyclotron resonance at room temperature for all samples studied. On cooling the spin-splitting was found to be temperature dependent. This is attributed to the importance of electron-electron interactions which couple the two spin transitions as observed recently in high purity GaAs/GaAlAs heterojunctions at low temperatures.

Abstract:

We have performed 4 K magnetotransport measurements on intrinsic InAs/GaSb multi quantum wells (MQWs) under hydrostatic pressure. Through careful configuration of the growth we are able to produce samples that have differing interface monolayers (either InSb or GaAs). Analysing the data to calculate the band overlap (Delta), we find that InSb-like samples have an overlap 30 meV larger than GaAs-like in good agreement with recent theoretical predictions.

Abstract:

We report studies of sequential resonant tunneling in GaAs/AlGaAs multi-quantum well p-i-n structures in the presence of parallel magnetic fields up to 15 T. New features are observed which are attributed to inter-Landau level resonances involving a change of Landau index of +1 and +2. In one of the samples the tunnelling resonances saturate and shift with the magnetic field. This result may be related to the similar effects observed in coupled two-dimensional electron gases at high magnetic fields.