Robin Nicholas

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.

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.