Positron annihilation spectroscopy was used to study the native vacancy distribution in a-plane hetero-epitaxial GaN. It was shown that the Ga vacancy concentration was independent of the layer thicknesses of 5 to 25μm. This was strikingly different from the behavior in c-plane GaN, where the Ga vacancy concentration decreased dramatically with distance from the GaN/sapphire interface. This difference in the native vacancy profiles was tentatively correlated with the differences in the O impurity and dislocation density profiles in the polar and non-polar materials.

Vacancy Defect Distribution in Heteroepitaxial a-plane GaN Grown by Hydride Vapor Phase Epitaxy. F.Tuomisto, T.Paskova, S.Figge, D.Hommel, B.Monemar: Journal of Crystal Growth, 2007, 300[1], 251-3