Native defect properties andp-type doping efficiency in group-IIA dopedwurtziteAlN

Abstract

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 $({V}_{\mathrm{N}})$ 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 $ϵ(0∕\ensuremath{-})$ for substitutional Be $({\mathrm{Be}}_{\mathrm{Al}})$, Mg $({\mathrm{Mg}}_{\mathrm{Al}})$, and Ca $({\mathrm{Ca}}_{\mathrm{Al}})$ are 0.48, 0.58, and $0.95\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, respectively. In $p$-type AlN, Be interstitials $({\mathrm{Be}}_{i})$, 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, ${\mathrm{Be}}_{i}$ are energetically not favorable. It is found that $p$-type doping efficiency of substitutional Be, Mg, and Ca impurities in $w\text{\ensuremath{-}}\mathrm{Al}\mathrm{N}$ is affected by atomic size and electronegativity of dopants. Among the three dopants, Be may be the best candidate for $p$-type $w\text{\ensuremath{-}}\mathrm{Al}\mathrm{N}$. N-rich growth conditions help us to increase the concentration of ${\mathrm{Be}}_{\mathrm{Al}}$, ${\mathrm{Mg}}_{\mathrm{Al}}$, and ${\mathrm{Ca}}_{\mathrm{Al}}$.