Electronic structures of defects in ZnO: hybrid density functional studies

Theoretical investigation of the defect energy levels in band gap for ZnO is of great importance to understand the photoluminescence (PL) spectrum in experiment. However, the "band-gap" problem in the density functional calculations leads to incorrect evaluation of the defect levels inside the band gap. In this work, we perform hybrid density functional calculation, which can accurately predict the band gap width and the gap states, to study the electronic structures of both native defects and doped impurities of Li, Na, K, and Ag in ZnO. Our results show that both the vacancies and octahedral self-interstitials of O and Zn contribute to the broad green PL spectrum observed in experiments. In addition, the gap states arising from these doped impurities are predicted, where some of the gap states match with the experimental values. Moreover, the characters of these gap states are discussed based on the calculated density of states.