Annealing Temperature, Time and Thickness Dependencies in (TCO) SnO₂ Thin Films Grown by Spray Pyrolysis Technique

Abstract

Tin oxide thin films were prepared by spray pyrolysis method using SnCl₂.2H₂O as starting precursor and deposited on glass substrate. Three groups of samples with different preparation conditions (temperature, time and thickness) were synthetized. The samples were characterized using Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), UV-Visible Spectroscopy and Van der Pauw four-point electrical measurements. The grain size in the samples changes from 80 to 500 nm. Optical and electrical parameters were measured or calculated, such as: band gap, refractive index, sheet resistance, transmittance spectrum and figure of merit. Film thicknesses were obtained from fringes features in the transmittance spectra with a variation from 76 to 761 nm. A mechanism of transformation from tin dichloride to tin oxide is proposed and discussed; additionally the visual yellow color of some samples, related with a low transparency, is associated to the amount of abhurite or tin hydroxide complex coexisting with tin oxide. The figure of merit showed that 500 °C, 42 sprays and 1 hour of annealing time were the best conditions in the preparation of SnO₂ with TCO properties.