| The family of III-V nitrides (GaN, InGaN, AlGaN) are currently the object of intense research due to their numerous applications, ranging from optoelectronic devices such as UV or blue-green light emitting diodes, laser diodes, and UV solar blind detectors, to high power/high temperature electronics. Many of these new devices and applications depend on the optical properties of GaN, such as the type of carriers involved in recombination and their lifetime. Carrier lifetime is critical for determining, for example, the frequency response of photoconducting detectors, the gain in bipolar transistors, and the conductivity modulation of thyristors. The lifetime is also a measure of material quality since it is directly affected by traps and recombination centers.; Time-resolved photoluminescence (TRPL) spectroscopy is a powerful experimental tool to investigate carrier dynamics due to the combination of temporal and spectral information. It provides valuable scientific understanding of the materials by investigating properties such as carrier lifetimes, non-radiative processes and optical non-linearities. However, many time domain optical processes are associated with local properties of the materials such as recombination at impurity or defect locations, lifetime in quantum confined systems, local piezoelectric effects and strain, and transport to and recombination near interfaces. Thus high spatial resolution in time dependent processes is required.; This work explores the use of time and spatially resolved photoluminescence experiments to elucidate recombination mechanisms on a macroscopic and microscopic scale in a variety of materials and quantum confined systems. Beginning with the presentation of the experimental instrumentation built to accommodate high temporal and spatial resolution, the dissertation goes on to apply spatially resolved TRPL to study recombination processes in GaN films and InAs self-assembled quantum dots (SAD's).; Typically, epitaxial GaN is grown on lattice mismatched substrates resulting in strained films. Thick films were examined in order to minimize the influence of the strain on the fundamental physical properties of the material system. It is shown, for the first time, that the recombination mechanism in bulk GaN is dominated by radiative recombination at room temperature, and the polariton character of free exciton at 4K is confirmed. In the case of epitaxial lateral overgrown GaN, the saturation of defect levels is responsible for a two-fold increase in the free exciton lifetime. It is also shown that sub-micron resolved photoluminescence studies identify, for the first time, the hydrostatic strain in epitaxial lateral overgrown GaN and its influence on the carrier lifetime. Band filling effects were identified and carrier lifetime was measured in the case of SAD's. |
