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 ultra-violet emission and the decay of the visible emission in photoluminescence spectra. The strong and dominant near-band-edge ultra-violet emission suggested acceptable luminescence behaviors of Na-doped ZnO.

Unexpected Positive Role of Oxygen Vacancies in Na-Doped ZnO. Yang, X.P., Lu, J.G., Zhang, H.H., Lu, B., Huang, J.Y., Ye, C.L., Ye, Z.Z.: Journal of Applied Physics, 2012, 112[11], 113510