III-Nitride semiconductor films and device structures grown by low-pressure MOCVD

III-Nitride materials, such as aluminum nitride, gallium nitride, indium nitride and their alloys, are wide bandgap semiconductors. Their exceptional physical properties, notably their wide energy bandgap, physical strength and chemical stability, make them ideal for many optoelectronic devices such as solar-blind ultraviolet photodetectors, blue and green light emitting diodes and laser diodes, high power electronics for use in numerous applications.; Unlike conventional semiconductors such as silicon or gallium arsenide which have a cubic symmetry, III-nitride semiconductors are wurtzite crystals with a hexagonal symmetry. In addition, because of their exceptional physical properties, the synthesis of III-Nitride crystals is much more difficult than conventional semiconductors. Many issues need to be solved prior to achieving device quality materials such as, for example, the choice of the substrate to be used for III-Nitride thin film growth, the development of an adequate growth technology and the optimization of the growth conditions, the understanding of the material physical properties.; In the present work, a simple crystallographic model for the interfacial structure and the epitaxial growth of wurtzite III-Nitride thin films on the (00.1) and (01.2) orientations of sapphire substrates is presented. A low pressure MOCVD reactor is optimized and the growth parameter space explored to achieve first high quality binary AlN and GaN, then ternary Al_xGa _1–xN and Ga_1–xIn_xN compounds, followed by heterostructures, including single heterostructures, quantum wells and superlattices. The growth of AlN, GaN and Al_xGa_1–xN epitaxial films on all-important silicon substrates is also investigated. The lateral epitaxial overgrowth of GaN on sapphire and silicon substrates is shown to dramatically reduce the density of defects in III-Nitride materials on both substrates. These advances in III-Nitride materials are validated by the demonstration of a range of optoelectronic and electronic devices, including ultraviolet photoconductors, Schottky metal-semiconductor-metal and p-i-n ultraviolet photovoltaic detectors, visible light emitters, and field-effect transistors.