Properties of highly oriented spray-deposited fluorine-doped tin oxide thin films on glass substrates of different thickness Original Research Article

Transparent conducting thin films of fluorine-doped tin oxide (FTO) have been deposited onto the preheated glass substrates of different thickness by spray pyrolysis process using SnCl4·5H2O and NH4F precursors. Substrate thickness is varied from 1 to 6 mm. The films are grown using mixed solvent with propane-2-ol as organic solvent and distilled water at optimized substrate temperature of 475 °C. Films of thickness up to 1525 nm are grown by a fine spray of the source solution using compressed air as a carrier gas. The films have been characterized by the techniques such as X-ray diffraction, optical absorption, van der Pauw technique, and Hall effect. The as-deposited films are preferentially oriented along the (2 0 0) plane and are of polycrystalline SnO2 with a tetragonal crystal structure having the texture coefficient of 6.19 for the films deposited on 4 mm thick substrate. The lattice parameter values remain unchanged with the substrate thickness. The grain size varies between 38 and 48 nm. The films exhibit moderate optical transmission up to 70% at 550 nm. The figure of merit (φ) varies from 1.36×10−4 to 1.93×10−3 Ω−1. The films are heavily doped, therefore degenerate and exhibit n-type electrical conductivity. The lowest sheet resistance (Rs) of 7.5 Ω is obtained for a typical sample deposited on 4 mm thick substrate. The resistivity (ρ) and carrier concentration (nD) vary over 8.38×10−4 to 2.95×10−3 Ω cm and 4.03×1020 to 2.69×1021 cm−3, respectively.