Non-axial NO-VZn shallow acceptor complexes in nitrogen implanted p-type ZnO thin films

Abstract Over the past two decades, there have been numerous reports about the p-type behavior of N-doped ZnO. To date, however, its origin still remains mysterious, especially, N ion-implanted ZnO system. Herein, ZnO films were implanted with 70 keV N ions to a fluence of 1 × 1017 cm−2 at room temperature, followed by annealing in the range of 750–950 °C. The obtained p-type ZnO films have a widely hole concentration of 2.87 × 1015 ~ 2.64 × 1016 cm−3, a mobility of 1.37 ~ 7.27 cm2V-1s−1 and a resistivity of 148.3 ~ 299.4 Ω.cm. The thermal evolution of point defects and the possible shallow acceptors in N-implanted ZnO films were further investigated by means of Raman scattering, Photoluminescence (PL) and Electron paramagnetic resonance (EPR). The results show that abundant intrinsic-related defects including zinc interstitials (Zni), oxygen vacancies (VO) and zinc vacancies (VZn) were introduced during ion implantation. It is demonstrated that appropriate post-annealing can not only reduce the compensation of donor defects, but also facilitate the formation of N-related shallow acceptor complexes, both of which contribute to the p-type conduction transition of N-implanted ZnO films. The non-axial NO-VZn complexes are proposed to be a kind of potential and stable acceptors in N ion-implanted ZnO films.