Picosecond Time-Resolved Studies of Semiconductors.

Available from UMI in association with The British Library. Requires signed TDF. This work uses time-resolved photoluminescence to study the dynamics of hot carriers in semiconductors, created by light pulses of picosecond duration. The experimental technique employed, consists of using a streak camera which is synchronized with the excitation laser pulses, to time -resolve photoluminescence. Three bulk GaAs samples have been studied, one undoped, one n-type and one p-type, with the intention of carrying out the first systematic study of carrier dynamics in this material, with the advantage of high quality samples, and good time resolution. It was concluded from this that some important relaxation mechanisms were not included in previous measurements such as the influence of a doped in component and the role played by the holes in the cooling process. Another aspect of interest in semiconductor physics was investigated by using modulation doped GaAs/AlGaAs MQWs, the dynamics of electrons and holes under low dimensionality was studied. One p-type sample was used, motivated by the fact that no such study of time-resolved hole dynamics in a quasi-2D system had been undertaken, and such information is extremely relevant from the technological and fundamental viewpoint. This study reveals the important scattering mechanisms, and it was found that under low excitation conditions the hole dynamics could be described by a simple bulk theory for GaAs. Nevertheless under high excitation conditions some anomalous effects were found. Three n -type MQWs with different well widths were studied, to try to find some effect in the cooling process due to the differing degrees of confinement. It is concluded that such effects are not particularly relevant, at least in studies with our time resolution, but some important remarks, and some suggestions for measurements that could probably detect such effects are made.