Native defect properties and p-type doping efficiency in group-IIA doped wurtzite AlN

Using the first-principles full-potential linearized augmented plane-wave (FPLAPW) method based on density functional theory (DFT), we have investigated the native defect properties and p-type doping efficiency in AlN doped with group-IIA elements such as Be, Mg, and Ca. It is shown that nitrogen vacancies (V(N)) have low formation energies and introduce deep donor levels in wurtzite AlN, while in zinc blende AlN and GaN, these levels are reported to be shallow. The calculated acceptor levels epsilon(0/-) for substitutional Be (Be(Al)), Mg (Mg(Al)), and Ca (Ca(Al)) are 0.48, 0.58, and 0.95 eV, respectively. In p-type AlN, Be interstitials (Be(i)), 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 are applied, Be(i) are energetically not favorable. It is found that p-type doping efficiency of substitutional Be, Mg, and Ca impurities in w-AlN is affected by atomic size and electronegativity of dopants. Among the three dopants, Be may be the best candidate for p-type w-AlN. N-rich growth conditions help us to increase the concentration of Be(Al), Mg(Al), and Ca(Al).