Robin Nicholas

Abstract:

The influence of the interface states on the cyclotron resonance (CR) of the broken-gap two carrier InAs/GaSb DHET system has been investigated. Enhanced coupling between electron and hole levels is observed in the samples with a monolayer of InSb formed at one of the interfaces, leading to evidence of strong interband transitions close to that of the electron CR. This is believed to be the result of the asymmetry introduced into the structure. The results are consistent with the theoretical analysis from self-consistent k·p calculations.

Abstract:

The quantum Hall effect in InAs/GaSb heterojunctions at very high fields and low temperatures when both the electrons and holes contribute to the quantized Hall conductance was studied. InAs/GaSb were grown by metal organic vapor phase epitaxy and are known to possess a relatively low level of extrinsic doping so that the majority of charge carriers are created by intrinsic charge transfer from the GaSb layers to the InAs layer. The Hall conductance showed a digital sequence oscillating from 0-1-0 conductance quanta and the diagonal resistivity showed oscillatory insulating behavior due to the formation of a total gap in the energy spectrum.

Abstract:

We present a theoretical study of intersubband transitions (IST) in InAs/GaSb superlattices in the presence of a parallel magnetic field. Starting from a model describing a single electron in a single quantum well and extending it to include many-body effects and the non-parabolicity of the InAs conduction band we are able to explain the recent cyclotron resonance experiments on narrow and wide InAs/GaSb quantum wells.

Abstract:

InGaAs/GaAs quantum well (QW) and quantum dot (QD) structures grown on GaAs (111)B substrates under different growing temperatures are investigated by magneto-photoluminescence (PL) up to 15 T in both Faraday and Voigt configurations. The spatial extents of the carrier wave functions (ECWFs) are deduced from the diamagnetic shift of the PL peak energy. The binding energies of the InGaAs/GaAs QWs are evaluated to be about 5 meV. The QW ECWFs in the growth direction obtained by the diamagnetic shift are consistent with those calculated by the k · p theory. The heights and radii of the InGaAs/GaAs QDs are also estimated from the ECWFs. In addition, we found that the in-plane ECWFs decreased slightly as the growth temperature was varied from 525 to 450°C. The ECWFs in the growth direction decreased when the growth temperature was varied from 525 to 480°C and then increased as the temperature was decreased to 450°C. © 2000 The Japan Society of Applied Physics.

Abstract:

The real and imaginary components of the GaAs refractive index at temperatures between 20-700 degrees C have been obtained. Measurements were made by comparing the variable angle reflectivity of p-polarized and s-polarized 633 nm wavelength light from a deoxidized GaAs surface. By using these temperature-dependent optical constants for GaAs, modeling has allowed the behavior of surface photoabsorption (SPA) signals with temperature and oxide layers present to be predicted for different angles of incidence. The experimentally observed SPA signals during deoxidization of GaAs show strong qualitative agreement with these calculations at each of the angles of incidence considered. The measurement of data and application to modeling provides a platform for the measurement of temperature-dependent optical data for other III-V materials and for the investigation of deoxidation mechanisms.