| III-V nitride semiconductors have outstanding electronic properties and are highly promising for various device applications. However, the development of a methodology for the growth of nitrides with high crystalline quality has remained the most severe obstacle to progress for decades with much of the difficulty deriving from the lack of native or lattice-matched substrates. Development of strategies to improve the crystalline quality of III-Nitride films requires an understanding of the growth mechanisms and microstructures of various epi-systems and the establishment of a detailed correlation between the structural properties of the crystals and their optical/electrical performance. Such understanding is still largely lacking in spite of an enormous research effort to date. In this work, we have carried out several in-depth studies which constitute significant contributions to this field. These include: (1) In depth studies and analysis of complex intersecting basal plane/prismatic stacking fault structures in GaN/AlN films grown on vicinal SiC substrates and determination of their formation mechanisms; (2) Studies of strain relaxation mechanisms of GaN/AlN epifilms grown on vicinal substrates, suggesting a model of geometrical partial misfit dislocations; (3) Studies of the correlation between the basal plane/prismatic plane stacking faults and low temperature photoluminescence peaks; (4) Development of a strategy to reduce threading dislocation densities in AlN grown on sapphire substrate by modify the growth mode through changes in both V/III ratio and overall flux rate during growth; (5) Studies of stress evolution during the early stages of AlN vapor growth; (6) Studies of the thermal stability of porous SiC substrates. |
