The etch-pit density of organometallic vapor-phase epitaxial samples on sapphire was found to be sharply reduced by the insertion of a low-temperature deposited AlN buffer layer, or a GaN buffer layer. It was assumed that the etch pits originated from microtubes, and these in turn were assumed to arise from screw dislocations. Therefore, insertion of a buffer layer could serve to block the threading of screw dislocations.

Reduction of etch-pit density in organometallic vapor-phase epitaxially-grown GaN on sapphire M.Iwaya, T.Takeuchi, S.Yamaguchi, C.Wetzel, H.Amano, I.Akasaki: Japanese Journal of Applied Physics - 2, 1998, 37[3B], L316-8