Interfacial and microstructural changes of the Al₂O₃/ZnO multilayer films induced by in-situ growth and post-annealing temperatures

Al₂O₃/ZnO nanolaminates are promising nanocomposites with special properties for the applications of oxide-based thin-film transistors, photoluminescence devices, and pitch grating references. In this study, Al₂O₃/ZnO nanolaminates were grown at 80 °C, 120 °C, 250 °C by atomic layer deposition, and then post-annealed by furnace annealing at 600 °C, 700 °C, 800 °C respectively. Both the in-situ growth temperature and post-annealing temperature-induced microstructures of Al₂O₃/ZnO nanolaminates were examined using x-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). In addition, the interfacial diffusion and solid-state reaction were systematically studied by high-resolution transmission electron microscopy (HRTEM). The films grown at 80 °C and 250 °C show a typical polycrystalline structure, while the film grown at 120 °C possesses an obvious preferred orientation. After post-annealing at 700 °C, the spinel ZnAl₂O₄ grains are formed at the interface of the Al₂O₃/ZnO films grown at 80 °C and 250 °C, which indicates the solid-state reaction has occurred, but this phenomenon did not occur for the films grown at 120 °C. The results indicate that the growth temperature not only affects the crystallinity and preferred orientation of the ZnO interlayers, but also the interfacial diffusion and counter-diffusion of atoms, and thereby the solid-state reaction, in the post-annealing process. So, simultaneously controlling the effects of the growth and post-annealing temperatures has great significance for this kind of nanolaminates.