Effect of an Oxidized Metallic Zn Buffer Layer on the Morphological, Optical, Electrical, and Photoresponse Properties of Spin-coated ZnO Films

We studied the morphological, optical, electrical, and photoresponse properties of ZnO thin films grown by using the sol-gel spin-coating method on Zn buffer layers oxidized at different temperatures ranging from 300 to 600 °C. With increasing the oxidation temperature, the surface morphology changed from granular to a cluster of aggregates. In the photoluminescence spectra, the highest ratio of the intensities of the near-band-edge to the deep-level emission and the lowest value of the full width at half maximum were observed at an oxidation temperature of 300 °C. The ZnO thin film grown on the Zn buffer layer oxidized at a temperature of 300 °C showed the highest values of transmittance in the visible region. The optical band gap was blue-shifted with decreasing oxidation temperature from 400 to 300 °C, and the lowest Urbach energy was observed at an oxidation temperature of 300 °C. In the study of the photoresponse properties, the fastest response/recovery rate and the highest photosensitivity were obtained for the sample prepared at an oxidation temperature of 300 °C.