Optical and electrical properties of pure and Sn4+-doped n-SnS films deposited by chemical bath deposition

Pure and Sn4+-doped SnS films with different S/Sn molar ratio were fabricated by chemical bath deposition from the solution of tin dichloride, thiacetamide, and triammonium citrate. The deposited films were characterized by X-ray diffraction, scanning electron microscopy, ultraviolet-visible spectrophotometry, photoluminescence spectrophotometry, and electrical conduction measurement. The effect of S/Sn molar ratios and Sn4+-doping on the properties of the films was investigated. When S/Sn molar ratio in bath solution was designed as 0.55–0.85, the S/Sn ratios in the films were ~0.54–0.83. The pure films showed electrical resistivity of ~26.2–71.3 k Ω cm, decreasing as decreasing S/Sn ratio. The Sn4+-doping further obviously decreased the resistivity of the films to ~1.5–9.6 kΩ cm. The films had thicknesses of ~470−650 nm and average transmittances of ~48.9−71.4% in the wavelength range of 290−1000 nm. The direct and indirect optical band gaps estimated from the transmittance and reflectance spectra equaled to ~1.25−1.83 eV and ~1.1−1.65 eV, respectively. The average transmittances and band gap values increased as decreasing S/Sn ratio and doping Sn4+-cation.