It was recalled that the threading dislocations which were caused by the coalescence of GaN islands, in the initial stages of low-pressure metalorganic chemical vapor deposition, were reduced in number by buffer layer annealing. Unlike the case of atmospheric-pressure metalorganic chemical vapour deposition, the high nucleation density in low-pressure metalorganic chemical vapour deposition made it difficult to form large isolated islands which enhanced lateral growth. It was demonstrated here that a buffer layer was transformed into isolated islands by annealing, and that the threading dislocations could be reduced in number by controlling the density of isolated islands. Nitridation of sapphire modified its surface energy and enhanced nucleation during buffer layer deposition; thus resulting in a buffer layer with a small grain size. Using annealing, an as-deposited buffer layer with a small grain size was transformed into isolated islands with an (00•1) facet on a flat (00•1) surface. This enhanced lateral growth at high temperatures. Longer nitridation times and shorter buffer layer deposition times led to a lower density of islands and thus a lower dislocation density. Samples with a low dislocation density exhibited a strong band-edge photoluminescence emission, with low yellow-band emission.

Reduction of Threading Dislocations in GaN on Sapphire by Buffer Layer Annealing in Low-Pressure Metalorganic Chemical Vapor Deposition T.Hashimoto, M.Yuri, M.Ishida, Y.Terakoshi, O.Imafuji, T.Sugino, K.Itoh: Japanese Journal of Applied Physics - 1, 1999, 38[12A], 6605-10