Point defects in group III nitrides: A comparative first-principles study

One of the main challenges in the development of wide bandgap semiconductor devices is to understand the behavior of defects and avoid their harm. Using density-functional theory calculations with hybrid functional, we systematically investigated the neutral and charged native point defects (vacancy, interstitial, and antisite defect) in GaN, AlN, and InN crystals in terms of local geometry relaxation, formation energies, and electronic and diffusion properties. By comparing the defect configuration and transition levels as a function of the Fermi level, we show that Ga interstitial (Ga-oc, Ga-te) in GaN, N vacancy (V-N), N interstitial (N-i), In antisite (In-N), and In interstitial (In-te, In-oc) in InN can exist stably only in the positive charge states with donor level and V-In is stable in the neutral state, while the other defects exhibit both donor and acceptor behavior. Among them, the most stable defects are identified as V-N for p-type nitrides and V-Ga, V-Al for n-type nitrides. These results, providing a mechanism for self-compensation effects, explain the reduced doping efficiencies for both n-type and p-type nitrides due to defects. Moreover, it is also demonstrated that N interstitial diffuses faster than vacancy, which are mainly responsible for the low concentration of N interstitials and N-based defect complexes produced in nitrides. Significantly, the trends of formation energy, transition level, and migration barrier of nitrides are also consistent with their intrinsic atomic size and bandgap. Our study is important for the identification and control of point defects in nitrides, which have a profound impact on device performance and reliability.