Observation of Native Ga Vacancies in GaN by Positron Annihilation

Positron annihilation experiments were performed to identify native point defects in n-type GaN bulk crystals as well as in epitaxial layers. The results show that Ga vacancies are present at concentrations ${10}^{17}–{10}^{18}{\mathrm{cm}}^{-3\mathrm{}}$ in both GaN bulk crystals and layers. The Ga vacancies are negatively charged, and their concentration correlates with the intensity of the yellow luminescence. We conclude that the Ga vacancies contribute to the electrical compensation of n-type GaN and that their acceptor levels are involved in the yellow luminescence transition.