Positron annihilation spectroscopy was used to study the high-pressure annealing induced thermal recovery of vacancy defects in free-standing GaN grown by hydride vapour-phase epitaxy. The results showed that the in-grown Ga vacancy complexes recover after annealing at 1500 to 1700K. Comparison of the experimental positron data with ab initio calculations indicated that the Doppler broadening measurement of the electron momentum distribution was sensitive enough to distinguish between the N and O atoms surrounding the Ga vacancy. It was shown that the difference between the isolated VGa in electron irradiated GaN and the VGa-ON complexes in highly O-doped GaN was clear, and the Ga vacancy related defect complexes that start dissociating at 1500K could be identified as VGa-ON pairs.

Dissociation of VGa-ON Complexes in HVPE GaN by High-Pressure and High-Temperature Annealing. F.Tuomisto, S.Hautakangas, I.Makkonen, V.Ranki, M.J.Puska, K.Saarinen, M.Bockowski, T.Suski, T.Paskova, B.Monemar, X.Xu, D.C.Look: Physica Status Solidi B, 2006, 243[7], 1436-40