Synthesis and Optical Properties of Fluorine-Doped Zinc Tin Oxide Thin Films Prepared by Ultrasonic Spray Pyrolysis

Thin films of fluorine-doped zinc tin oxide (FZTO) were prepared by ultrasonic spray pyrolysis (USP) at various concentrations of Zn and F. The defect levels in the bandgap were determined by the photoluminescence (PL) measurements. Optical transitions between defect and band levels were identified by the analysis of the absorption spectra. The ascription of defect levels to oxygen vacancies was supported by the measurements of x-ray photoelectron spectroscopy (XPS).

Band diagrams were sketched to show the obtained defect levels and related optical transitions. Three states of point defects were determined in the bandgap. They were attributed to the neutral, singly- and doubly-ionized oxygen vacancies. The obtained results were in agreement with previous measurements of fluorine tin oxide (FTO) and theoretical predictions of tin dioxide. The study provides deep insight into the optical processes of FZTO, which might have its imprint on evaluating the future utility of this material in various applications.