Positron annihilation spectroscopy was used to study the thermal behavior of various native vacancy defects which were typical of free-standing GaN, grown by hydride vapor phase epitaxy under high-pressure annealing at various annealing temperatures. The results showed that the VGa-ON pairs dissociated and that Ga vacancies annealed out from the bulk of the material at 1500 to 1700K. A binding energy of 1.6eV was determined for the pair. Thermal formation of Ga vacancies was observed at annealing temperatures above 1700K; indicating that Ga vacancies were created thermally at the high growth temperature, but their ability to form complexes such as VGa-ON governed the fraction of vacancy defects which survived cooling.

Thermal Stability of In-Grown Vacancy Defects in GaN Grown by Hydride Vapor Phase Epitaxy. F.Tuomisto, K.Saarinen, T.Paskova, B.Monemar, M.Bockowski, T.Suski: Journal of Applied Physics, 2006, 99[6], 066105