A low-energy positron beam, and secondary ion mass spectrometry, were used to study defects in homo-epitaxial and hetero-epitaxial layers. The results revealed high concentrations of Ga vacancies in nominally undoped n-type material, where the conductivity was due to unintentional O incorporation. The Ga vacancies were observed in both homo-epitaxial and hetero-epitaxial layers; thus indicating that their formation was independent of the dislocation density. No Ga vacancies were detected in p-type or semi-insulating samples that were doped with Mg; as predicted by the theoretical formation energies. In samples where n-type conductivity was due to Si doping, and the incorporation of O impurities was suppressed, the concentration of Ga vacancies was much lower than that in n-type samples which contained O. This indicated that the presence of O donors promoted the formation of Ga vacancies. It was suggested that this effect was due to the creation of VGa-ON complexes during epitaxial growth.

Influence of Dopants and Substrate Material on the Formation of Ga Vacancies in Epitaxial GaN Layers. J.Oila, V.Ranki, J.Kivioja, K.Saarinen, P.Hautojärvi, J.M.Baranowski, K.Pakula, T.Suski, M.Leszczynski, I.Grzegory: Physical Review B, 2001, 63[4], 045205 (8pp)