The origin of threading dislocations in epitaxial layers which had been grown on (00•1) sapphire was investigated by examining, by means of transmission electron microscopy, the various stages of high-temperature GaN growth on low-temperature GaN nucleation layers. The results indicated that, after 20s of high-temperature growth, the GaN islands were free of threading dislocations. After 75 or 120s of growth, most of the islands contained pure screw (c-type) and pure edge (a-type) threading dislocations, with interspersed mixed (c+a type) threading dislocations. Most of the latter originated from faulted regions which were located within nucleation layers. The threading dislocations moved towards the island’s upper surface (c-type) or curved towards the island’s side-facets (a type or c+a type). The coalescence of high-temperature GaN islands did not give rise to a, c or c+a type threading dislocations. After 240s of growth, most of the threading dislocations were of a-type and could result from the climb and glide of basal-plane dislocations which formed via the dissociation of Shockley partials which were located within the faulted regions. Basal-plane dislocations were also observed which were attached to the side-facets of islands away from the faulted regions. It was noted that c type and c+a type threading dislocations formed mainly via the coalescence of Frank partials near to the GaN/sapphire interface.

Origins of Threading Dislocations in GaN Epitaxial Layers Grown on Sapphire by Metalorganic Chemical Vapour Deposition. V.Narayanan, K.Lorenz, W.Kim, S.Mahajan: Applied Physics Letters, 2001, 78[11], 1544-6