Robin Nicholas

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.

Abstract:

The new technique of Far InfraRed Modulated PhotoLuminescence (FIRM-PL) has been used to study the properties of a high mobility 2-D electron gas in a series of GaAs/AlGaAs heterojunctions and quantum wells. When the occupancy of the lowest Landau level is between 1 and 2 very large transfers of PL intensity are observed at the cyclotron resonance condition. The FL intensity is transferred from the E-0 line to F-1 corresponding to emission from the first two quantised electric subbands. A study of the power dependence of this signal allows us to deduce that the relative recombination efficiencies of the two lines are around 5 orders of magnitude different in such structures. This difference leads to a very high sensitivity for this technique for the observation of internal excitations within the electron system. In quantum wells signals are seen for all occupancies due to transfer between PL from higher Landau levels.