Morphological and optical properties of low temperature processed SnO2 :F

Abstract

Thin films of transparent conducting fluorine doped tin oxide (SnO2:F) on soda lime glass and stainless steel substrates are prepared by spray pyrolysis at low temperature ≤250 °C. Optical properties in the form of complex dielectric function (ϵ = ϵ1 + iϵ2) spectra are obtained using spectroscopic ellipsometry from 0.035 to 5.89 eV for SnO2:F on glass and from 0.75 to 5.89 eV for SnO2:F on stainless steel. The absorption coefficient (α) spectra are extracted from spectra in ϵ for the film on soda lime glass from 0.035 to 5.89 eV and on stainless steel from 0.75 to 5.89 eV. Direct band gaps for SnO2:F thin films on soda lime glass and stainless steel substrates are determined to be 3.45 ± 0.01 and 3.60 ± 0.01 eV, respectively. Infrared extended measurement shows an absorption feature at 0.063 eV (508 cm−1) which may be attributed to Sn–O and Sn–F bonding. A broad background phonon absorption feature due to Sn–OH and O–H bonding is also identified at 0.3 eV (2420 cm−1). Resistivity is deduced from ϵ. Improved agreement between optically and electrically determined resistivity is obtained when the infrared range spectrum is analyzed. The morphologies of both the films are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM).