Preparation, characterization and electronic properties of fluorine-doped tin oxide films

Abstract

Tin oxide (SnO₂) and fluorine doped tin oxide (FTO) films were prepared on glass substrates by sol-gel spin-coating using SnCl₄ and NH₄F precursors. Fluorine doping concentration was fixed at 4 at% and 20 at% by controlling precursor sol composition. Films exhibited the tetragonal rutile-type crystal structure regardless of fluorine concentration. Uniform and highly transparent FTO films, with more than 85% of optical transmittance, were obtained by annealing at 600 °C. Florine doping of films was verified by analyzing the valence band region obtained by XPS. It was found that the fluorine doping affects the shape of valence band of SnO₂ films. In addition, it was observed that the band gap of SnO₂ is reduced as well as the Fermi level is upward shifted by the effect of fluorine doping.

Keywords

tin oxide films / fluorine doping / energy band diagram

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