Using the first-principles full-potential linearized augmented plane-wave method based upon density functional theory, an investigation was made of the native defect properties and p-type doping efficiency in AlN doped with group-IIA elements such as Be, Mg and Ca. It was shown that N vacancies (VN) had low formation energies and introduce deep donor levels in wurtzite AlN, while in zincblende AlN and GaN, these levels were reported to be shallow. The calculated acceptor levels ε(0/−) for substitutional Be (BeAl), Mg (MgAl), and Ca (CaAl) were 0.48, 0.58 and 0.95eV, respectively. In p-type AlN, Be interstitials (Bei), which act as donors, have low formation energies, making them a likely compensating center in the case of acceptor doping. Whereas, when N-rich growth conditions were applied, Bei were energetically not favourable. It was found that p-type doping efficiency of substitutional Be, Mg, and Ca impurities in w-AlN was affected by atomic size and electronegativity of dopants. Among the 3 dopants, Be was thought to be the best candidate for p-type w-AlN. Nitrogen-rich growth conditions helped to increase the concentrations of BeAl, MgAl, and CaAl.

Native Defect Properties and p-Type Doping Efficiency in Group-IIA Doped Wurtzite AlN. Y.Zhang, W.Liu, H.Niu: Physical Review B, 2008, 77[3], 035201 (5pp)