Properties of N-doped ZnO thin films in annealing process

N-doped ZnO (ZnO:N) thin films were prepared by magnetron sputtering using NH3 as the N-doping source. The as-grown ZnO:N films showed high resistivity ∼103 Ω cm due to the hydrogen passivation effect. The properties of ZnO:N films under various annealing conditions (e.g., temperature, environment, and duration) were systematically studied with the aim of achieving p-type conductivity. The lowest room-temperature resistivity was found to be 7.73 Ω cm for p-type ZnO films annealed at 500  ∘C for 10 min in N2, with the hole concentration of 9.36×1017 cm−3 and Hall mobility of 0.86 cm2 V −1 s−1. Optical absorption spectra were performed to analyze the behaviors of hydrogen and nitrogen in p-type doping of ZnO. The NO–H complexes were largely present in as-grown ZnO films, which could be dissociated by thermal annealing resulting in activated N acceptors. Thus, the p-type conductivity was achieved in annealed ZnO:N films. A hydrogen-assisted nitrogen-acceptor doping mechanism was proposed as an answer for the achievement of p-type ZnO.