Mechanism for self-compensation in heavily carbon doped GaN

Heavy carbon (C) doping is of great significance for semi-insulating GaN in power electronics. However, the doping behaviors, especially the atomic configurations and related self-compensation mechanisms, are still under debate. Here, with the formation energy as the input parameter, the concentrations of C defects with different atomic configurations are calculated by taking the configurational entropy into account. The result shows that the concentrations of tri-carbon complexes (CNCiCN, where C-i refers to interstitial carbon) and dicarbon complexes (CNCGa) cannot be neglected under heavy doping conditions. The concentration of CNCiCN can even exceed that of C-N at sufficiently high doping levels. Especially, we suggest that it is the tri-carbon complex CNCiCN, instead of the commonly expected C-Ga, that acts as the self-compensation centers in semi-insulating GaN under heavy C doping conditions. The results provide a fresh look on the long-standing problem about the self-compensation mechanisms in C doped GaN.