A first-principles study of carbon-related complexes and energy levels in GaN using heyd-scuseria-ernzerhof hybrid functionals

Abstract

Carbon (C) is a common and important impurity in GaN. C doping is employed to obtain semi-insulating buffer layers, which are used for high electron mobility transistors. However, increasing C concentration means the increase of C-related trap levels in GaN, which causes detrimental effects to the device performance. These unexpected C-related trap levels are observed in a number of experiments, but the physical origins of these levels are still unknown. We performed first-principles calculations within density functional theory using hybrid density functionals. Our focuses were on the C-related complexes, about which very little is known so far. From the formation energies of various C-related complexes we obtained thermal and optical activation energies of the trap levels and directly compared them with the experimental values in order to identify the physical origins of the experimentally observed trap levels.