Structural properties of SnO₂: F films deposited by spray pyrolysis

Abstract

Transparent and conducting thin films of SnO₂ and SnO₂: F were deposited on alkali-free Corning 7059 substrates by spray pyrolysis. The effect of various process parameters such as doping level of fluorine (in solution), substrate temperature during deposition, thickness of the film and carrier gas (air) flow rate, on the film properties was investigated by x-ray diffraction during their optimization. The optimization of the thickness was done to get the maximum value of the ratio of average visible transmission to the specific resistivity. The films deposited with the optimized process parameters have a sheet resistance of 4 ω an average visible transmission of 86% (0.4-0.9 μm) and a thickness of 0.165 μm. The electrical conductivity of the SnO₂: F films was 10⁵ω^-1 cm^-1. The films were polycrystalline and the oxide phase observed was SnO₂ in cassiterite structure. In most of the cases the films preferentially oriented along [200]. This preferred orientation of the films was probably due to the oriented overgrowth of the films within a certain range of each process parameter. This has been explained on the basis of the standard deviation from the powder diffraction condition. It was concluded that low temperature growth was a result of adsorption-desorption phenomena whereas high temperature growth was a result of homogeneous nucleation. Since doping generally favours defect induced film growth, heavily doped films were randomly oriented. Rearrangement of grains in the films was apparent for thicker films.