A systematic positron annihilation spectroscopy study was made of Mg-doped, co-doped and annealed GaN films made by metalorganic chemical vapor deposition. The GaN:Mg films were free of detectable vacancy defects up to [Mg] ~ 3 x 1018/cm3 but, at doping levels above 1019/cm3, vacancies were observed. Two defects were identified: VN-MgGa pairs and vacancy clusters, where the number of missing atoms was estimated to be about 60. The defects had an inhomogeneous depth profile, with a layer of higher defect concentration starting 100nm below the surface. Thermal annealing dissociated the VN-MgGa pairs and the vacancy clusters, which migrated and formed an homogeneous distribution of smaller clusters throughout the film. The identified defects played an important role in the electrical compensation and activation of the Mg acceptors in GaN films, and exhibited correlations with the results of transmission electron microscopy and photoluminescence studies.

Role of Open Volume Defects in Mg-Doped GaN Films Studied by Positron Annihilation Spectroscopy. S.Hautakangas, K.Saarinen, L.Liszkay, J.A.Freitas, R.L.Henry: Physical Review B, 2005, 72[16], 165303 (10pp)