Chemical, vibrational and optical signatures of nitrogen in ZnO nanowires

ZnO nanowires with various concentrations of nitrogen molecules have been fabricated by remote plasma annealing. X-ray absorption near-edge spectroscopy (XANES) reveals that nitrogen exists mainly in two chemical states: atomic nitrogen substituting oxygen (NO) and molecular nitrogen (N2) weakly bound to the ZnO lattice; the latter state increases substantially with prolonged plasma time. Cathodoluminescence microanalysis of individual nanowires reveals a broad emission band at 3.24 eV at 10 K, attributable to the recombination of a shallow donor and a N2 acceptor state. The Raman modes at 547 and 580 cm−1 from the N-doped nanowires are found to rise in proportion to the N2 concentration, indicating they are related to N2 molecules or defects caused by the incorporation of N2 in the nanowires.