Be and Mg co-doping in GaN

We investigate co-doping of Be and Mg in GaN by molecular beam epitaxy with radio frequency plasma for nitrogen source. The compressive strain accumulated during the growth due to high doping of Be, which has shorter bond length than that of Ga, is compensated for by adding Mg, since its bond length is longer than that of Ga. Photoluminescence spectra reveal that both Be and Mg atoms are mainly incorporated in Ga sites and act as acceptors. The energy shift of the donor-acceptor pair emission associated with Be suggests possible correlation between co-doped Be and Mg acceptors.