Interaction energies between Na ((a) NaZn and (b) Na i ) and VO in various models. The black line with squarish dots is in neutral charge states and the red line with rounded dots denotes charged states. The insets show the sketch of models with dashed lines indicating the distance between Na and VO.
Formation energies as a function of Fermi-level position for various models for Zn-rich condition. The zero of Fermi level corresponds to the VBM. Only segments corresponding to the lowest energy charge states are shown. The slope of these segments indicates the charge state. Kinks in the curves indicate transitions between different charge states.
Formation energies of NaZn and Na i as a function of VO concentration under the Zn-rich (also Na-rich) condition.
Electronic band structures of ZnO supercells of charged defects Models MV (b), MN (c), MA (d) and (e), and perfect ZnO (a). The dashed line denotes Fermi level. The arrows refer to defect levels.
Top view SEM images of ZnO NRAs. (a) is ZnO:Na NRAs, the inset is micrograph; (b) is intrinsic ZnO NRAs.
Room-temperature PL spectra of (a) intrinsic ZnO, (b) as-grown ZnO:Na, and (d) annealed ZnO:Na NRAs.
High resolution XPS spectrums of different NRAs. (a) Nominally undoped NRAs, (b) as-grown ZnO:Na NRAs, (c) annealed ZnO:Na NRAs, and (d) the area ratio of P i of O 1s peak.
Calculated formation energies (in eV) for native point defects in ZnO under the Zn-rich condition.
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