| Popis: |
This thesis describes an experimental investigation of the photoluminescence emissions from firstly, bulk In0.53 Ga0.47 As and secondly, InGaAs\InP and AlAs\GaAs quantum well structures, as a function of hydrostatic pressure. Two high pressure systems have been developed and successfully used in the course of this work, an 8kbar piston and cylinder system and a miniature diamond anvil cell. From the high pressure measurements on the bulk InGaAs, both at room anti liquid nitrogen temperatures, it is shown that the pressure dependence of the direct band-edge luminescence is non-linear and independent of temperature. Using an empirical equation of state and making some assumptions as to the value of the bulk modulus, it is found that the band-edge luminescence is linearly dependent upon the lattice constant and may be described by a band-edge deformation potential of -8.25 +/- 0.1eV. Theory compares favourably with this value. From low temperature measurements of both quantum well systems it has been possible to deduce a quantitative description of how the conduction and valence band-edge discontinuities vary as a function of the applied pressure. It is shown that the band-offset ratio changes with pressure. This work constitutes the first observation of this phenomenon which had previously been thought either too small to be of consequence, or simply ignored. It is found that the conduction-band discontinuity in InGaAs\InP quantum wells decreases at -2.3 +/- 0.6meV/kbar while its valence-band discontinuity remains constant. The valence-band discontinuity in the AlAs\GaAs superlattice is directly measured to increase at +1.1 +/- 0. ImeV/kbar. An analysis of reported data for A1 Ga As/GaAs quantum wells shows that the pressure coefficient of the X l-x valence-band discontinuity is linearly dependent upon the alloy composition x. Theories of band-offset ratios and in particular the "model-solid" theory of Van de Walle and Martin (Van de Walle 1987), agree exceedingly well with these experimental findings. It is suggested that such agreement lends weight to the assumption that heterojunction band-edge discontinuities are intrinsic to the bulk properties of the host materials. |
