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: ${\mathrm{N}}_{\mathrm{O}},{\mathrm{N}}_{\mathrm{Zn}}$, 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.

• Received 13 June 2014
• Revised 3 May 2015

DOI:https://doi.org/10.1103/PhysRevB.92.024103