Positron annihilation experiments were performed in order to identify native point defects in n-type bulk crystals, as well as in epitaxial layers. The results showed that Ga vacancies were present in concentrations of between 1017 and 1018/cm3; in both bulk crystals and epitaxial layers. The Ga vacancies were negatively charged, and their concentration was related to the intensity of the yellow luminescence. It was concluded that the Ga vacancies contributed to the electrical compensation of n-type material, and that their acceptor levels were involved in the yellow luminescence transition.

K.Saarinen, T.Laine, S.Kuisma, J.Nissilä, P.Hautojärvi, L.Dobrzynski, J.M.Baranowski, K.Pakula, R.Stepniewski, M.Wojdak, A.Wysmolek, T.Suski, M.Leszczynski, I.Grzegory, S.Porowski: Physical Review Letters, 1997, 79[16], 3030-3