Analysis of the structural and optoelectronic properties of semiconductor materials and devices using photoacoustic spectroscopy and synchrotron x-ray topography

摘要

This thesis deals with the characterisation of semiconductor materials and devices through two complimentary experimental modalities. Synchrotron X-ray topography and photoacoustic spectroscopy are rapid, non-destructive and non-invasive techniques. The former may be used to elucidate the strain within a crystalline material due to localised structural defects causing deviations in the recorded X-ray intensity; whilst the latter can indirectly probe the non-radiative de-excitation processes within the bandstructure by measuring pressure variations within the gas in contact with the sample.ududIn the first half of this work, a review of the theoretical description of the photoacoustic effect in condensed matter samples is presented. This classical review is extended to encompass the photoacoustic effect in semiconductor materials. Criteria governing the design o f a spectrometer are then extracted. A photoacoustic spectrometer based on the gas-microphone technique, with a wide spectral range (0.5 eV to 6.2 eV) was designed and constructed. The spectrometer was characterised across its spectral range using common semiconductor materials.ududThe latter half of the thesis commences with a review of the kinematical and dynamical theories of X-ray diffraction. The properties of synchrotron radiation are discussed, with particular focus on their applicability to X-ray topography. The large area, section and grazing incidence topography techniques are presented. Several topographic studies of semiconductor materials and devices were performed. These included an analysis of the evolution of strain in ultra-bright light emitting diodes under varying degrees of electrical stress, strain induced by the epitaxial lateral overgrowth of gallium nitride on sapphire, stress due to rapid thermal processing of silicon wafers, characterisation of diamond crystals for use in a high energy monochromator, misfit dislocation generation at a Si/SiGe heterointerface and dynamical imaging of microdefects in nearly perfect silicon.