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-Be_Ga) complex, and 0.46 eV for (H-Mg_Ga) complex. Congruently, the binding energy is 1.40 eV for (H-Be_Ga), and 0.60 eV for (H-Mg_Ga). Owing to the lower binding energy, (H-Mg_Ga) is not thermally stable. As Be is incorporated in Mg-doped GaN, a (H-Mg_Ga) 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-Be_Ga) 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.