Sodium-doped ZnO nanowires grown by high-pressure PLD and their acceptor-related optical properties

Sodium-doped ZnO (ZnO:Na) nanowires were grown with a high-pressure pulsed-laser deposition process on silicon substrates using sputtered gold particles as catalysts. The introduction of sodium dopants into ZnO nanowires was confirmed by both X-ray diffraction spectrum and X-ray photoelectron spectroscopy. The morphology and microstructural changes in ZnO nanowires due to sodium doping were investigated with scanning electron microscope, high-resolution transmission electron microscope, and Raman spectrum. Detailed photoluminescence studies of ZnO:Na nanowires revealed characteristic sodium acceptor-related peaks, for example, neutral acceptor-bound exciton emission (A⁰X, 3.356 eV), free-to-neutral-Acceptor emission (e, A⁰, 3.314 eV), and donor-to-Acceptor pair emission (DAP, 3.241 eV). This indicated that sodium doping induces stable acceptor level with a binding energy of 133 meV in ZnO:Na nanowires.