Molecular nitrogen acceptors in ZnO nanowires induced by nitrogen plasma annealing

Abstract

X-ray absorption near-edge spectroscopy, photoluminescence, cathodoluminescence, and Raman spectroscopy have been used to investigate the chemical states of nitrogen dopants in ZnO nanowires. It is found that nitrogen exists in multiple states: ${\mathrm{N}}_{\mathrm{O}},\phantom{\rule{0.16em}{0ex}}{\mathrm{N}}_{\mathrm{Zn}}$, and loosely bound ${\mathrm{N}}_{2}$ molecule. The results establish a direct link between a donor-acceptor pair emission at 3.232 eV and the concentration of loosely bound ${\mathrm{N}}_{2}$. This work confirms that ${\mathrm{N}}_{2}$ at Zn site is a potential candidate for producing a shallow acceptor state in N-doped ZnO as theoretically predicted by Lambrecht and Boonchun [Phys. Rev. B 87, 195207 (2013)]. Additionally, shallow acceptor states arising from ${\mathrm{N}}_{\mathrm{O}}$ complexes have been ruled out in this paper.