It as recalled, in this review, that calculations had shown that the unintentional n-type conductivity that had often been observed in as-grown GaN could not be attributed to N vacancies, but was due to the unintentional incorporation of donor impurities. Native point defects could play a role in compensation and in phenomena such as yellow luminescence, which could be attributed to Ga vacancies. In a section on impurities, specific attention was focussed on dopants. Here O, which was commonly present as a contaminant, was a shallow donor in GaN but became a deep level in AlGaN due to a DX transition. Also, Mg was almost universally used as a p-type dopant, but hole concentrations were still limited. Reasons for this behavior were proposed, and alternative acceptors were examined. Finally, H played an important role in p-type GaN, and the mechanisms that underlay its behavior were explained. Incorporating H along with acceptors was an example of co-doping, and a critical analysis of co-doping was presented.

First-Principles Calculations for Defects and Impurities - Applications to III-Nitrides. C.G.Van de Walle, J.Neugebauer: Journal of Applied Physics, 2004, 95[8], 3851-79