Abstract The growth of high quality ZnO thin films is a hot research topic in the field of optoelectronic materials. In this study, high quality ZnO thin films with a… Click to show full abstract
Abstract The growth of high quality ZnO thin films is a hot research topic in the field of optoelectronic materials. In this study, high quality ZnO thin films with a double-layer structure were obtained by sol-gel method. Al-doping induced transition from polycrystals to single crystals in the ZnO thin films was found. The results show that Al-doping improves the c-axis orientation of ZnO thin films. When the Al-doping concentration is higher than 4at%, the frustum of hexagonal pyramid (FHP) shaped ZnO nanostructures are formed on the polycrystalline ZnO thin films surface. As the Al-doping concentration further rises, the areal density of the FHP-shaped nanostructures also gradually increases and the size becomes more uniform. Both SAED patterns and high-resolution TEM images indicate that the FHP-shaped ZnO nanostructures are single crystals. It is of great scientific significance to transform polycrystalline ZnO into single crystal ZnO by Al-doping combined with a simple heat-treatment process. Compared with pure ZnO thin films, the FHP-shaped nanostructures on the surface show better UV emission performance, suggesting these materials are ideal ones for the preparation of ZnO-based UV emitters. The authors propose that the growth mechanism of FHP-shaped ZnO nanostructure is a multi-step solid-solid reaction dominated by surface diffusion of zinc atoms.
               
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