Gallium vacancy complexes were identified in n-type bulk material by means of positron annihilation spectroscopy. Their formation was suppressed when the material became resistive by Mg doping; as expected from the behavior of the VGa formation energy as a function of the Fermi level. In Be-doped material, vacancies were observed even in resistive material. The positron lifetimes showed that their open volume was larger than expected for the N vacancy. A possible identification was that it was a VN–BeGa complex, in which the atoms that neighboured the N vacancy were strongly relaxed outwards; thus increasing the open volume.

Vacancies as Compensating Centers in Bulk GaN - Doping Effects. K.Saarinen, V.Ranki, T.Suski, M.Bockowski, I.Grzegory: Journal of Crystal Growth, 2002, 246[3-4], 281-6