The etch-pit density of organometallic vapor-phase epitaxial material, grown onto sapphire, was found to be markedly reduced by the insertion of a low-temperature deposited AlN buffer layer or GaN buffer layer between high-temperature grown GaN on sapphire. The insertion of a low-temperature deposited buffer layer between high-temperature grown GaN was effective in eradicating etch pits. Low-temperature deposited AlN and GaN buffer layers were both effective in eradicating etch pits. It was assumed that the causes of the etch pits were micro-tubes because, if micro-tubes were present at the surface, they would become enlarged due to the etching. The origin of the micro-tubes was considered to be screw dislocations. However, further work was required in order to clarify the relationship between etch pits and dislocations. The insertion of a low-temperature deposited buffer layer might have the effect of stopping the threading of screw dislocations.

M.Iwaya, T.Takeuchi, S.Yamaguchi, C.Wetzel, H.Amano, I.Akasaki: Japanese Journal of Applied Physics - 2, 1998, 37[3B], L316-8