Doping in these materials was considered on the basis of state-of-the-art first-principles calculations. In the case of n-type doping, it was found that N vacancies were too high in energy to be incorporated during growth and were not responsible for unintentional n-type conductivity, whereas Si and O could be incorporated in large numbers and were likely to cause unintentional n-type doping. The properties of O, including a propensity to DX-center formation, suggested that it was the main cause of unintentional n-type conductivity. The DX transition did not occur in zincblende material. The Ga vacancies were thought to be the likely source of yellow luminescence. In the case of p-type doping, it was found that the solubility of Mg was the main factor which limited the hole concentration in GaN. The incorporation of Mg at interstitial sites or antisites was not a problem. It was noted that H had a beneficial effect upon p-type doping because it suppressed compensation and enhanced acceptor incorporation. The compensation of acceptors by N vacancies could occur, and became increasingly marked as the Al-content of AlGaN alloys was increased. No other acceptor impurity exhibited characteristics that were superior to those of Mg.

C.G.Van de Walle, C.Stampfl, J.Neugebauer: Journal of Crystal Growth, 1998, 189-190, 505-10