Three GaN epilayers grown onto commercially available cone-patterned sapphire substrates by metal organic vapour phase epitaxy were investigated. Voltage dependence of monochromatic cathodoluminescence was used to investigate the threading dislocation behaviours. Fewer threading dislocation were observed in cathodoluminescence images when the penetration depth of electron was made shorter by altering the acceleration voltage from 30 to 5kV. It was shown that many threading dislocations were generated on the peaks of the cones, in-between cones, and in the coalescence regions, while there was almost no threading dislocations above the slopes of the cones. When the growth pressure was changed from 200 to 100Torr during the final stage, fewer threading dislocations were observed in cathodoluminescence images, and the full-widths at half-maximum for the (002) and (102) reflections’ X-ray diffraction rocking curves decreased. Furthermore, when the growth temperature was decreased from 1040 to 1000C during the middle stage, a clear hexagonal distribution of threading dislocations was observed and the full-widths at half-maximum for the (002) and (102) reflections’ X-ray diffraction rocking curves further decreased. Atomic force microscopy was used to investigate the surface morphology of the samples. In situ optical reflectivity spectra were measured to monitor the growth mode during the different growth stages. Based on the cathodoluminescence and reflectivity spectra results, the process of threading dislocation evolution and distribution was deduced and sketched.

Evolution and Control of Dislocations in GaN Grown on Cone-Patterned Sapphire Substrate by Metal Organic Vapor Phaseepitaxy. Y.B.Tao, T.J.Yu, Z.Y.Yang, D.Ling, Y.Wang, Z.Z.Chen, Z.J.Yang, G.Y.Zhang: Journal of Crystal Growth, 2011, 315[1], 183-7