Effect of thermal evolution of point defects on the electrical properties of nitrogen-implanted ZnO thin films

Abstract

Raman backscattering spectroscopy and X-ray photoelectron spectroscopy have been applied to study thermal evolution of point defects as a function of post-annealing temperature in nitrogen-implanted ZnO thin films (ZnO:N). Zni-related donor defects (e.g., Zni-NO complexes or Zni clusters) are prone to dissociation to form a freely moving isolated Zni defect by post-annealing process, which is extremely advantageous for achieving a p-type transition of the ZnO:N film. However, lots of Ni atoms induced by ion implantation could migrate to the near-surface of the films to form NC/NH/NO species with increasing post-annealing temperature, resulting in a lower concentration of NO acceptor defects in ZnO:N films. In addition, although post-annealing at higher temperatures can form more No acceptor defects, the newly generated (N2)O double donor defects have a severe self-compensating effect. Consequently, the concentration of both the Zni-related donors and effective acceptors gradually decreases at elevated post-annealing temperatures, which is the reason why all ZnO:N films present n-type conductivity and do not convert to p-type conductivity.