The annealing of n-type thin GaN films, grown by metalorganic chemical vapour deposition in vacuum, was studied by means of beam-based positron annihilation spectroscopy. The results were consistent with a model in which Ga vacancies, VGa, existed alongside dislocations and were stable at up to 900C. It was suggested that the dislocations were shallow positron traps. Upon annealing at up to 500C, a decrease in dislocation density increased the effective positron diffusion length and the probability of trapping at VGa. While the effective positron diffusion length continued to change, the trapping of positrons at VGa saturated upon annealing above 500C. The formation of N vacancies near to the surface at high temperatures was suggested to introduce a potential which retarded positron back-diffusion. At 900C, the dissociation of GaN at a rate of about 5nm/s was observed. Clusters of O, stable at 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