Structural and morphological investigation of non-basal-plane gallium nitride by vapor phase epitaxy with a special emphasis on nonpolar m-plane .

The success of current GaN-based device technologies owe largely to both scientific and technical development of conventional +c plane vapor phase epitaxy. Recently, non +c plane (non-basal-plane and --c plane) GaN epitaxy has been attracting significant attention due to its potential to outperform +c plane based devices. Therefore, at the present stage enormous background knowledge is under development, not only to demonstrate traditional technologies on non-basal-plane orientations, but also to understand the essential materials science that will provide insight into the future development of the GaN-based materials. In this work, heteroepitaxy and homoepitaxy of nonpolar m-plane GaN were extensively studied. For the growth methods, two of the major GaN vapor phase epitaxy techniques, i.e. hydride vapor phase epitaxy (HVPE) and metal organic chemical vapor deposition (MOCVD) were employed. Numerous characterization techniques were used to analyze the surface morphology and structural quality. First, the origin of surface instability commonly reported for heteroepitaxial nonpolar m-plane films was determined to be associated basal-plane stacking fault (BSF) defects. Here, a novel x-ray diffraction method was established by modifying the interpretation of Williamson-Hall analysis and to conveniently quantify the density of BSF. Two of the defect reduction techniques (lateral epitaxial overgrowth (LEO) and nano-masking) were investigated for HVPE on the nonpolar m-plane orientation, which showed significant reduction in both threading dislocations and BSFs as well as improvements in optical properties. Also, the mound formation phenomenon of homoepitaxial m-plane GaN grown by MOCVD was explored. The characteristic slope angles and shapes of mounds depended on the growth parameters. In this regard, the optimum surface miscut angles for suppression of mound formation were estimated for specific growth conditions, revealing good agreement with experimental results via successfully grown atomically flat surfaces. Finally, quasi-equilibrium crystal shapes of wurtzite GaN were investigated. Here, the widely accepted selective-area-growth method was found to be strongly influenced by gas diffusion, therefore a different experimental method was proposed. Specifically, the growth rate polar diagrams and kinetic Wulff constructions were developed using planar growths on different twelve crystal orientations.