Professor Robert Taylor

Abstract:

Time-resolved photoluminescence experiments in a wide carrier density range up to and beyond the threshold for stimulated emission in ZnSe/ZnSxSe1-x. superlattices are presented. Different localisation mechanisms of free excitons are identified giving rise to different radiative recombination channels. At high carrier density localised energy states merge into miniband that allows for exciton-exciton interaction, such as screening of the free-exciton absorption and inelastic exciton-exciton scattering.

Abstract:

We present a combined experimental and theoretical investigation of intra- and intersubband carrier relaxation in GaAs/AlAs quantum wells following femtosecond laser excitation at low density. Time-resolved optical absorption has been measured using 125 fs pulses from a tunable Ti:sapphire laser which allows carriers to be excited preferentially into different subbands. The experiments have been analyzed using a multi-subband Monte Carlo simulation which contains all the important scattering mechanisms. Electron-phonon scattering rates obtained from dielectric continuum theory have been used, and we find excellent agreement with the experiment. The dominance of interface phonons in intrasubband relaxation is confirmed. © 1995 American Institute of Physics.

Abstract:

We report time-resolved optical transmission and photoluminescence measurements of exciton dynamics and recombination in a ZnSe/ZnSe 0.82S0.18 superlattice which displays low-threshold lasing. The carrier densities in our experiments are below threshold for stimulated emission. We find clear evidence for strong exciton-LO phonon scattering which gives rise to emission at the same wavelength where stimulated emission is reported to occur.

Abstract:

We report time-resolved luminescence measurements of MBE-grown ZnTe/GaSb. Above-bandgap excitation is provided by second-harmonic generation using infrared pulses from a Ti:sapphire laser. Cooling of the hot-carrier distribution is observed on a picosecond time-scale, and is seen to be limited by phonon bottle-necking at these carrier densities, allowing an estimate of the LO phonon lifetime in this material.