Mg acceptor activation mechanism and hole transport characteristics in highly Mg-doped AlGaN alloys**Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFB0403100 and 2017YFB0403101), the National Natural Science Foundation of China (Grant Nos. 61704149, 61674076, and 61605071), the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BY2013077, BK20141320, and BE2015111), the Project of Science

Abstract

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 (VIII complex)1− as well as 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 AlxGa1 − 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.