Hydrogen depassivation of the magnesium acceptor by beryllium in p-type GaN

Under nitrogen-rich growth conditions, the present ab initio study predicts that hydrogen passivation is more effective on the acceptor Be instead of Mg in a co-doped p-type GaN. The formation energy is 0.24 eV for (H-BeGa) complex, and 0.46 eV for (H-MgGa) complex. Congruently, the binding energy is 1.40 eV for (H-BeGa), and 0.60 eV for (H-MgGa). Owing to the lower binding energy, (H-MgGa) is not thermally stable. As Be is incorporated in Mg-doped GaN, a (H-MgGa) may release a H+ cation at relatively elevated temperatures. Consequently, the H+ diffuses swiftly away from a Mg-Ga, across a barrier of 1.17 eV, towards a Be-Ga and forms a stable (H-BeGa) with it. The activation of Mg acceptors can be thus facilitated. In this view, the process of hydrogen depassivation of the Mg acceptor by Be can convert the as-grown high-resistivity Mg-doped GaN into a p-conducting material, as observed in the experiments.