Sapphire substrates showed nanosized surface pits after the growth of GaN layers using a two-step process by hydride vapour-phase epitaxy. Threading dislocations with Burgers vectors of c and c + a were found to originate from the pits. Cross-sectional transmission electron microscopy observations were used to elucidate the mechanism of dislocation generation.

Sapphire Surface Pits as Sources of Threading Dislocations in Hetero-Epitaxial GaN Layers. F.Y.Meng, I.Han, H.McFelea, E.Lindow, R.Bertram, C.Werkhoven, C.Arena, S.Mahajan: Scripta Materialia, 2011, 65[3], 257-60