Mg acceptor activation mechanism and hole transport characteristics in highly Mg-doped AlGaN alloys

The Mg acceptor activation mechanism and hole transport characteristics in AlGaN alloy with Mg doping concentration (～ 10²⁰ cm^-3) grown by metal-organic chemical vapor deposition (MOCVD) are systematically studied through optical and electrical properties. Emission lines of shallow oxygen donors and (V_III complex)^1- as well as V_N³⁺ and neutral Mg acceptors are observed, which indicate that self-compensation is occurred in Mg-doped AlGaN at highly doping levels. The fitting of the temperature-dependent Hall effect data shows that the acceptor activation energy values in Mg-doped Al_xGa_1-xN (x=0.23, 0.35) are 172 meV and 242 meV, and the hole concentrations at room temperature are 1.2×10¹⁸ cm^-3 and 3.3×10¹⁷ cm^-3, respectively. Therefore, it is believed that there exists the combined effect of the Coulomb potentials of the dopants and screening of the Coulomb potentials by a high hole concentration. Moreover, due to the high ionized acceptors' concentration and compensation ratio, the impurity conduction becomes more prominent and the valence band mobility drops sharply at low temperature.