Electronic and optical properties of fluorine-doped tin oxide films

Abstract

Thin films of fluorine-doped SnO2 have been prepared by deposition on borosilicate glass using the spray-pyrolysis technique. The effect of doping on the concentration and mobility of the charge carriers (electrons) as well as the resistivity of the films has been studied. The undoped films had a resistivity of a few m Ω cm; this could be reduced by a factor of 10 by doping. The electron mobility in undoped films was about 3 cm2/Vs but could be improved by a factor of 5 to 6 by doping. The doping yield was about 2.3%. The high quality films which were deposited for photovoltaic applications had a sheet resistance of R□=2 Ω/sq and an average transmittance, in the visible region, of T=85% for a thickness of 1.1 μm. Their figure of merit is one of the highest values reported: φ=T10/R□≈0.1 S. The optical dispersion of our films can be explained perfectly by classical models. In the wavelength region of λ<0.580 μm, the refractive index, N, for undoped and doped films can be given by N=[1+λ2/(0.370λ2−0.0105)]1/2, where λ is in μm. From the study of dispersion and the plasma resonance frequency, the numerical values at optical frequencies of the dielectric constant, electron mobility, and electron effective mass were determined as 3.70, 9.3–11.8 cm2/Vs, and (0.26–0.45)m0, respectively, where m0 is the mass of free electrons. From the variation of direct and indirect optical transition energies with the carrier concentration, the density-of-states effective masses for electrons and holes were obtained as 0.85 m0 and 0.78 m0, respectively. These studies revealed a direct energy bandgap of 4.11 eV for SnO2 in addition to a defect band situated 0.45 eV above the valence band edge.

Doping properties of monoclinic BiVO4studied by first-principles density-functional theory

“…On the other hand, p-type and n-type doping of metal oxides may also be realized by introducing impurities to O sites [36][37][38][39][40][41][42][43][44][45][46]. In this case, C, N, and F are the most considered impurities.…”

Mechanisms of Ion Detection for FET-Sensors Using FTO: Role of Cleaning Process, pH Sequence and Electrical Resistivity

“…The advantages of using this material rely on its physical/chemical characteristics. For example: FTO is a n-type semiconductor with a large band gap (between 3.9~4.6 eV) [36][37][38] ; when produced by spray pyrolysis method, FTO presents interesting, very promising and useful physicalchemistry characteristics such as potential to be miniaturized, high transparence on visible spectrum region, high surface area, large conductivity range, mechanical hardness, thermal stability and biocompatibility.…”

Band alignment of TiO2/FTO interface determined by X-ray photoelectron spectroscopy: Effect of annealing

“…Determining heterojunction valence and conduction band offsets and the ability to tune them to a desired application would have an obvious impact on the performance optimization of devices. 13 Fluorine-doped tin oxide (FTO) film is a kind of popular transparent conductive oxide with a low resistivity of 10 −4 Ωcm and high transparency of 90% in the visible region, 14 in addition to indium tin oxide (ITO) and aluminum doped zinc oxide (AZO). Because of its high chemical stability, energy level matching and good electron transport, titania (TiO 2 ) is always deposited on FTO substrate to form a TiO 2 /FTO heterojunction, which has been widely used as the photo-anode for the electron exportation in various organic thin film solar cells.…”