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: N O , N Zn , and loosely bound 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 N 2 . This work confirms that 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 N O complexes have been ruled out in this paper.

Raman investigation of N‐implanted ZnO: Defects, disorder and recovery

“…This is clearly vivid in other experiments where variation of N 2 pressure during growth or variation of sample temperature during ion implantation results in different site occupation of atomic N in ZnO. In this regard, the formation of molecular N 2 , either at V Zn or V O site, is possible and has been investigated also. The former one is reported to be a shallow acceptor, whereas the latter is a major source of compensating donor .…”

“…In literature, N‐induced modifications of defects/defect complexes in ZnO have been investigated using different spectroscopic techniques . The Raman mode near 275 cm −1 is known to be due to atomic nitrogen in the vacant oxygen sites (N O ) in ZnO .…”

“…In this regard, the formation of molecular N 2 , either at V Zn or V O site, is possible and has been investigated also. The former one is reported to be a shallow acceptor, whereas the latter is a major source of compensating donor . It has been proposed that doped N acts as deep acceptors in ZnO and compensating donors such as V O s become more energetically favorable .…”

Identification of a Nitrogen-related acceptor in ZnO nanowires

“…[32][33][34] The energy level of the N acceptor, however, can be affected by its local surrounding, 35 complexing with residual group III impurities 36 and intrinsic defects, [37][38][39] as well as formation of N-N molecules. 40,41 Moreover, it was also suggested that the proximity to the surface lowers the formation energies of the N-related acceptors and modifies their photoionization processes. [42][43][44] This may be partly responsible for the promoted p-type conductivity in nanostructured ZnO, 21,28,40,45 though the exact physical mechanism responsible for this effect, as well as the local structure of the incorporated N acceptors, remains unknown.…”

“…40,41 Moreover, it was also suggested that the proximity to the surface lowers the formation energies of the N-related acceptors and modifies their photoionization processes. [42][43][44] This may be partly responsible for the promoted p-type conductivity in nanostructured ZnO, 21,28,40,45 though the exact physical mechanism responsible for this effect, as well as the local structure of the incorporated N acceptors, remains unknown.…”