Impact of vacuum annealing on the multifunctional properties of RF-sputtered ZnO thin films

Abstract

Zinc oxide (ZnO) is a versatile wide bandgap semiconductor extensively used in electronics, optoelectronics, and sensor technologies due to its excellent optical transparency, high electron mobility, and environmental stability. In this work, the effect of vacuum annealing on RF sputtered ZnO thin films was studied within a temperature range of 400 degrees C-600 degrees C. The structural, microstructural, optical, mechanical and electrical properties were studied with annealing. Compared to the as deposited film, the crystallite size increases significantly at 400 degrees C and showed little variation at higher temperature, as confirmed in the micrographs. The transmittance also increased for 400 degrees C and then it remained almost constant. PL studies showed reduced visible emissions with annealing due to the conversion of Zn-i-related defects into non-radiative states. Electrical conductivity increased significantly due to annealing, reaching its highest value at 600 degrees C which was supported by the increased carrier concentration and mobility measurements. However, the mechanical properties degraded upon annealing, which can be explained by grain growth which is in accordance with the Hall-Petch effect, where coarser grains reduce the hindrance to dislocation motion. These findings highlight the temperature-sensitive trade-offs between electrical performance and mechanical stability in vacuum-annealed ZnO thin films, which is critical for optimizing their use in various device applications.