Study of structural and optical properties of ZnO thin films produced by sol-gel methods

This study adopted sol-gel and spin-coating methods for fabricating ZnO thin films on Pt/ Ti/Si substrates. Each layer is carbonized at a low temperature and inally sintered at a high temperature for spin-coating. The luminescent characteristics of ZnO films were investigated using photoluminescence (PL). The crystal structures of the films were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical states of ZnO thin films. The platinum and aluminum layers were deposited as top and bottom electrodes, respectively. The sandwich structure of electroluminescence (EL) elements was fabricated and its conductivity was measured. The SEM images showed that the surface roughness of the thin films and the grain size improved as the thickness of the films increased. These results were verified by XRD patterns in which the peak intensities of the ZnO (002) C preferred orientation increased as the thin films thickened. In addition, enhanced crystallinities increased the ultraviolet (UV) radiation intensities of the ZnO thin films. Moreover, only UV radiation excited through the intrinsic band gap was observed in the PL spectra, and no visible light was produced by the luminescence mechanisms of defects. Moreover, the chemical configuration analysis of the thin films revealed that the proportions of O-Zn bonding and Vo increased and decreased respectively as the number of spincoated layers increased. These results indicate that increased thin film thickness reduces thin film internal defects and improves the ZnO structure. Regarding the EL measurements of the EL elements, at a ZnO film thickness of 530 nm, the threshold and alternating-current working voltages were 25 and 33 V, respectively.