High-Pressure Photoluminescence of Semiconductor Structures

Available from UMI in association with The British Library. High pressure photoluminescence has been used to study semiconductor structures. The measurements have been made in a miniature cryogenic diamond anvil cell (DAC). The results reported cover a wide range of materials and many different aspects are discussed. This in part serves to demonstrate the versatility and importance of the technique. New developments in DAC technology are fully described, in particular the introduction of electrical feedthroughs and the importance of the gasket geometry. The technologically important material system GaAs/Al_{rm x}Ga _{rm 1-x}As has been studied under hydrostatic pressure. Band offsets and their pressure dependencies are determined with spectroscopic accuracy and show interesting deviations from the expected behaviour. The effect of substrate orientation on the band offsets has also been investigated. The binding energy of excitons in GaAs/AlAs superlattices in the vicinity of Gamma-X (Type I to Type II) crossover is measured for the first time. The emerging new material systems containing strained layers have been studied, particularly In_ {rm x}Ga_{rm 1-x}As grown pseudomorphically on GaAs. In this system the pressure coefficients of the PL from strained quantum wells are found to have an unexpected dependence on the composition. Comparison with strained InAs/InP quantum wells suggests that this is in fact a strain effect rather than alloy. The band line-up in In_ {rm x}Ga_{rm 1-x}As/GaAs and In_{rm x}Ga_{rm 1-x} As/Al_{rm y}Ga _{rm 1-y}As quantum well structures is determined from the crossing of Gamma and X states. A preliminary study of the dilute magnetic semiconductor Cd_{rm 1-x}Mn _{rm x}Te is made. High pressure magnetic field measurements on this material are expected to yield information on the nature of the exchange interactions. To this end CdTe/CdMnTe superlattices have been characterised under hydrostatic pressure. Films of a-Si:H are studied under pressure. The intensity of the PL is found to be maintained upto ~90 kbar, in contrast with previous published data. The PL exhibits a small red shift of 1.9 meV/kbar which is compared with the pressure coefficients of the PL from other amorphous materials.