Density-functional pseudopotential calculations for native point defects and dopant impurities were used to investigate the doping of AlxGa1-xN alloys. Two causes for an experimentally observed decrease in n-type conductivity, at x-values greater than 0.4, were identified. That is, in the case of doping with O, a DX transition converted the shallow donor into a deep level. The other cause involved compensation by cation vacancies. In the case of p-type doping, a reduction in doping efficiency with increasing x-value was attributed to compensation by N vacancies and to an increase in the Mg acceptor ionization energy. Various alternative acceptor impurities were also investigated, but none of them exhibited overall characteristics which were superior to those of Mg. Only Be was a possible candidate, although its action could be impeded by compensation due to Be interstitial donors.

Doping of AlGaN Alloys. C.Stampfl, J.Neugebauer, C.G.Van de Walle: Materials Science and Engineering B, 1999, 59[1-3], 253-7