Native Point Defects in GaN: A Hybrid-Functional Study

We present a systematic study of properties of common native point defects in GaN based on hybrid density-functional calculations. These defects include vacancies, interstitials, antisites, and common complexes. Using configuration coordinate diagrams, we estimate the likelihood of defects to be radiative or nonradiative. Our results show that gallium vacancies exhibit a large magnetic moment in the neutral charge state and are most likely nonradiative. This is in contrast to nitrogen vacancies, which are probable sources of the experimentally observed green-luminescence band peaking at 2.35 eV in undoped GaN. We also show that infrared photoluminescence (PL) bands that are created by 2.5-MeV electron irradiation in GaN can be explained by the formation of native defects. Namely, the interstitial gallium is likely to be responsible for the narrow infrared PL band centered around 0.85 eV, with a phonon fine structure at 0.88 eV; the gallium-nitrogen divacancies are possible sources of the broad PL band with a peak at 0.95 eV.