Effects of post heat treatments on ZnO thin-films grown on Zn-coated teflon substrates

ZnO thin films were first grown on Zn-coated Teflon substrates using a spin-coating method, with various post-heating temperatures. The structural and optical properties of the ZnO thin films were then investigated using field-effect scanning-electron microscopy, X-ray diffractometry, and photoluminescence (PL) spectroscopy. The surface morphology of these ZnO thin films exhibited dendritic structures. With increasing post-heating temperature, all samples preferentially exhibited preferential c-axis orientation and increased residual tensile stress. All of the films exhibited preferential c-axis orientation, and the residual tensile stress of those increased with increasing post-heating temperature. The near-band-edge emission (NBE) peaks were red-shifted after post-heating treatment at 400 °C. The intensity of the deep-level emission (DLE) peaks gradually decreased with increasing post-heating temperature. Moreover, the narrowest 'full width at half maximum' (FWHM) and the highest intensity ratio of the NBE to the DLE for thin films, were observed after post-heating at 400 °C. The ZnO thin films fabricated with the 400 °C post-heating process provided the highest crystallinity and optical properties.