Optical properties of silver-doped zinc oxide thin films: an optimization study

Silver (Ag), not only alters the electrical and optical properties of ZnO thin films but also has the ability to enhance its ultraviolet (UV) emission. However, the mechanism for the UV emission enhancement has not been clearly understood. The study focused on optimization of the optical properties of pristine and Ag-doped ZnO films through variation of preparation and post deposition parameters. The prepared pristine and Ag-doped ZnO films were found to be polycrystalline in nature with diffraction peaks corresponding to ZnO and Ag phases. Increase in Ag and annealing temperature led to increase in the transmittance of Ag-doped ZnO films. The refractive index was found to increase with a decrease in substrate-source distance, an increase in Ag concentration, film thickness, and annealing temperature. The extinction coefficient for the analysed films was found to decrease with increase in substrate-source distance and annealing temperature, but increased with increase in film thickness. An inherent dissipation of electromagnetic energy in pristine and Ag-doped ZnO films was observed due to strong interaction between low and wide optical band gap energies of Ag and ZnO, respectively. The optical band gap energy increased with an increase in substrate-source distance, decreased with an increase in film thickness and annealing temperature at a wavelength,lambda=650nm\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda =650\,\text{nm}$$\end{document}. The observed trends have been explained based on polarizability, reduced structural defects, thermal expansion, and lattice vibrations in pristine and Ag-doped ZnO films. The obtained optimized properties show that Ag-doped ZnO films are good candidates for optoelectronic applications.