Positron annihilation measurements revealed that negative Ga vacancies were the predominant acceptors in n-type samples grown by means of hydride vapor phase epitaxy. The concentration of Ga vacancies decreased, from more than 1019, to below 1016/cm3 as the distance from the interface region increased from 1 to 300µm. These concentrations were the same as the total acceptor densities determined using Hall experiments. The O depth profile was similar to that of VGa; thus suggesting that the Ga vacancies were complexed with the O impurities.

Ga Vacancies as Dominant Intrinsic Acceptors in GaN Grown by Hydride Vapor Phase Epitaxy. J.Oila, J.Kivioja, V.Ranki, K.Saarinen, D.C.Look, R.J.Molnar, S.S.Park, S.K.Lee, J.Y.Han: Applied Physics Letters, 2003, 82[20], 3433-5