Thermal evolution of zinc interstitial related donors in high-quality NH3-doped ZnO films

In this paper, the authors have investigated the thermal evolution of the forms, density, and electrical properties of the zinc interstitial (Zni) related donors in NH3-doped ZnO films via annealing the as-grown sample at different temperatures. The relatively high crystalline quality has eliminated the effect from grain boundaries and thus guaranteed the validity of the study. Generally, in the presence of nitrogen, the main forms of Zni are the Zni-N omicron complexes and the Zni small clusters. When increasing the annealing temperature to a moderate level (around 700 degrees C), the dissociation of the Zni and the NO in the Zni-N omicron complexes would make them partially desorb from the sample. Meanwhile, part of the isolated Zni created from the dissociation would aggregate to form the Zni small clusters (Zni-Zni). When increasing the annealing temperature to 900 degrees C, the desorption of the Zni-N omicron complex would continue, but the Zni small clusters are no longer thermally stable. They would decompose into isolated Zni atoms and finally desorb from the sample. As the Zni-N omicron complexes and the Zni small clusters are both shallow donors, their gradual desorption while increasing the annealing temperature results in a reduced compensation level. Furthermore, using the NH3 as the nitrogen doping source could bring in a complex shallow acceptor in the form of (NH4) Zn. Simultaneously, annealing at high temperatures (900 degrees C) may result in the clustering of zinc vacancies. Therefore, the current method proposed in this work could be a feasible path to enhancing the p-type doping efficiency in nitrogen-doped ZnO material. (C) 2017 Optical Society of America