Photoluminescence studies of impurity transitions in Mg-doped AlGaN alloys

Deep ultraviolet photoluminescence spectroscopy was employed to study the impurity transitions in Mg-doped AlGaN alloys. A group of deep level impurity transitions was observed in Mg-doped Al_xGa_1-xN alloys, which was identified to have the same origin as the previously reported blue line at 2.8 eV in Mg-doped GaN and was assigned to the recombination of electrons bound to the nitrogen vacancy with three positive charges (V _N³⁺) and neutral Mg acceptors. Based on the measured activation energies of the Mg acceptors in AlGaN and the observed impurity emission peaks, the V_N³⁺ energy levels in Al _xGa_1-xN have been deduced for the entire alloy range. It is demonstrated that the presence of high density of V_N³⁺ deep donors translates to the reduced p-type conductivity in AlGaN alloys due to their ability for capturing free holes.