Accelerating the formation of high-quality optical surface layer in ZnO thin films by the increase of heat-treatment temperature

Abstract As an important optoelectronic material, ZnO thin film has been used in lots of fields such as antireflection optical coatings, photoluminescence-based sensors, photocatalysts, etc. Many studies have demonstrated that the characteristics of the surface layer of ZnO thin film (such as crystalline state, point defect types, number of point defects, roughness, etc.) dominate its physical properties and thus determine the performance of the optoelectronic or microelectronic device prepared from it, so how to effectively control the characteristics of the surface layer is worthy of in-depth study. In this investigation, we prepared ferric chloride doped ZnO thin films and explored the effect of heat-treatment temperature on the crystalline state and luminescence behavior of the surface layer. The results show that all samples possess a double-layer structure: the bottom layer is a conventional ZnO layer composed of polycrystalline particles, while the top layer is made up of dense pyramid-like nanostructures. These pyramid-like nanostructures have good crystalline quality and high c-axis orientation. The increase of the heat-treatment temperature accelerates the formation of a high-quality optical surface layer in the ZnO thin film, and the formation of this high-quality surface layer in turn greatly improves the ultraviolet emission efficiency of the ZnO thin film.