Positron annihilation spectroscopy was used to show that 2MeV electron irradiation at 300K created primary Ga vacancies at an introduction rate of 1/cm. The Ga vacancies recovered in long-range migration processes at 500 to 600K, with an estimated migration energy of 1.5eV. Since the native Ga vacancies in as-grown GaN survived at 1300 to 1500K, it was concluded that they were stabilized by forming complexes with O impurities. The estimated binding energy (2.2eV) of such complexes was in good agreement with the results of theoretical calculations.

Thermal Stability of Isolated and Complexed Ga Vacancies in GaN Bulk Crystals. K.Saarinen, T.Suski, I.Grzegory, D.C.Look: Physical Review B, 2001, 64[23], 233201. See also: Physica B, 2001, 308-310, 77-80