Properties of fluorine-doped SnO2 films prepared by the pyrosol deposition method

Fluorine-doped SnO₂ (SnO₂:F) films were prepared in ordinary atmosphere on heated Corning 7059 glass substrates by the pyrosol deposition method with solutions consisting of SnCl₄·5H₂O, NH₄F, CH₃OH, H₂O and HCl. It was found that the substrate temperature and the chemical composition of the solutions largely affect the deposition rate and the properties of the SnO₂:F films. Under the optimized deposition condition, a resistivity as low as ≈4.3 × 10⁻⁴ Ω cm and a specular transmittance of ≈79% could be attained for a ≈0.6 μm thick film. X-ray diffraction measurements showed that these films were polycrystalline with the tetragonal cassiterite structure and grew with a (200) preferred orientation. The surface morphology observed by scanning electron microscopy changed from round-shape to pyramidal-shape above a substrate temperature of 450°C. A similar change in the surface morphology also took place when the CH₃OH/H₂O mol ratio in solution was less than 0.1. X-ray photoelectron spectroscopy indicated that the fluorine concentrations in the films, being significantly diminished, also increase with increasing the fluorine concentrations in the starting solutions.