Unexpected positive role of oxygen vacancies in Na-doped ZnO.

The interaction of Na impurities and O vacancies (VO) in ZnO was studied in theory and experiment. The VO facilitated substitutional Na (NaZn/NaZn-) acceptors with inhibiting interstitial Na (Nai/Nai+) donors, which may benefit the p-type conductivity. The formed (NaZn-VO)+/0 complexes induced the change of band structures of ZnO, with the broadening of gap energies and disappearance of the VO2+-related impurity level, which confirmed by the blue shift of the near-band-edge (NBE) UV emission and the decay of the visible emission in PL spectra. The strong and dominant NBE UV emission suggested acceptable luminescence behaviors of Na-doped ZnO. [ABSTRACT FROM AUTHOR]