After considering the evidence for the existence of interstitials or vacancies in as-grown GaN, the results of a study which used 2.5MeV electron irradiation to produce such defects were described. After in situ irradiation at 4.2K, interstitial Ga was detected in a broad photoluminescence band, at 0.95eV, produced by the irradiation. The interstitial was observed in what appeared to be 2 distinct configurations. They were stable during annealing at up to room temperature, where long-range migration then occurred; as reflected by their disappearance and by the emergence of new and more stable defects. Conversion between the 2 configurations could be induced by optical excitation at 1.8K. Two possible models were considered. In one, the 2 interstitial sites were the 2 available sites (T and O) in the wurtzite lattice. In the other, both sites were T-sites but one was closer to its Ga vacancy than was the other. In both models, the 0.95eV band resulted from hole capture by the nearby Ga vacancy (before room temperature annealing), or by the remaining isolated vacancies after the Ga interstitials had disappeared during annealing. This implied that the stability of the 0.95eV band at up to 500C, together with an optically-detected electron paramagnetic resonance signal that appeared to be associated with it, showed that the isolated Ga vacancy was stable up to 500C.

Intrinsic Defects in GaN - What we are Learning from Magnetic Resonance Studies. G.D.Watkins, K.H.Chow, P.Johannesen, L.S.Vlasenko, C.Bozdog, A.J.Zakrzewski, M.Mizuta, H.Sunakawa, N.Kuroda, A.Usui: Physica B, 2003, 340-342, 25-31