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

Abstract

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 SnCl 4·5H 2O and NH 4F 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 SnO 2 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 ( R s) of 7.5 Ω is obtained for a typical sample deposited on 4 mm thick substrate. The resistivity ( ρ) and carrier concentration ( n D) vary over 8.38×10 −4 to 2.95×10 −3 Ω cm and 4.03×10 20 to 2.69×10 21 cm −3, respectively.