The formation mechanism and stability of p-type N-doped Zn-rich ZnO films

Abstract

Nitrogen-doped Zn-rich ZnO films [ZnO:(Zn, N)] were deposited on quartz substrates using a radio-frequency (RF) magnetron sputtering and ion implantation technique. Hall-effect measurements confirmed that a p-type ZnO:(Zn, N) film with a hole concentration of ~1016 cm−3, which exhibits significantly higher stability than p-type ZnO:N film prepared under non-Zn-rich conditions, is obtained by optimized post-annealing condition. With the help of X-ray photoelectron spectroscopy, Auger electron spectroscopy, Raman spectroscopy (Raman), ultraviolet and visible spectrophotometer and first-principles calculations, it is found that a certain concentration of zinc interstitial (Zni) donor defects which easily bond to substitutional nitrogen (NO) to form defect complexes (denoted as Zni@NO) were observed in the p-type ZnO:(Zn, N) film. Further theoretical and experimental investigations indicate that the relatively stable p-type conductivity of ZnO:(Zn, N) film is attributed to the formation of passive complex (Zni–2NO), which can form an impurity band (IBM) above the valence band maximum, resulting in a decrease in the acceptor ionization energy and an improvement in the stability of p-type ZnO:(Zn, N) film. This p-type formation mechanism is consistent with donor–acceptor co-doping method. Nevertheless, the p-type performance of the ZnO:(Zn, N) film would still gradually decline over time. The remaining interstitial nitrogen atoms (Ni) in p-type film is easy trapped by the acceptor NO to form a dual-donor defect (N2)O, which is one of possible important factors for the eventual instability of p-type ZnO:(Zn, N) films.