Layers with different crystalline quality were grown on a c-plane sapphire substrate at 1400C by metal-organic vapour phase epitaxy. Dislocations in AlN were mostly edge-type, which was generated at the grain boundaries. The density of this type of dislocation was high in a narrow area compared with pure edge-type dislocations caused by the misfit between substrate and epilayer. As the film became thicker and thicker, dislocations at the grain boundaries were dispersed. The core structure of dislocations was also revealed by high-resolution transmission electron microscopy.

Microstructure of Threading Dislocations Caused by Grain Boundaries in AlN on Sapphire Substrates. M.Imura, H.Sugimura, N.Okada, M.Iwaya, S.Kamiyama, H.Amano, I.Akasaki, A.Bando: Physica Status Solidi C, 2008, 5[6], 1582-4