The annealing of n-type thin GaN films grown by metal-organic chemical vapour deposition in vacuum was studied by beam-based positron annihilation spectroscopy. The results were consistent with a model in which Ga vacancies (VGa) exist alongside dislocations and were stable up to 900C. It was suggested that dislocations were shallow positron traps. Upon annealing at up to 500C, the decrease of dislocation density increased the effective positron diffusion length (L+eff) and the probability of trapping at VGa. While L+eff continues to change, the trapping of positrons at VGa was saturated upon annealing above 500C. The formation of N vacancies near to the surface at high temperatures was considered to introduce a potential that retards positron back-diffusion. At 900C, dissociation of GaN at a rate of about 5nm/s was observed. Oxygen clusters, stable up to 900C, appeared to exist near to the interface between the GaN film and the sapphire substrate.

Defects in GaN Films Studied by Positron Annihilation Spectroscopy. X.D.Pi, P.G.Coleman, C.L.Tseng, C.P.Burrows, B.Yavich, W.N.Wang: Journal of Physics - Condensed Matter, 2002, 14[12], L243-8