Substrate temperature effect on structural, optical and electrical properties of vacuum evaporated SnO2 thin films

Tin oxide (SnO2) thin films were deposited on glass substrates by thermal evaporation at different substrate temperatures. Increasing substrate temperature (Ts) from 250 to 450 °C reduced resistivity of SnO2 thin films from 18×10−4 to 4×10−4▒ Ω ▒cm. Further increase of temperature up to 550 °C had no effect on the resistivity. For films prepared at 450 °C, high transparency (91.5%) over the visible wavelength region of spectrum was obtained. Refractive index and porosity of the layers were also calculated. A direct band gap at different substrate temperatures is in the range of 3.55−3.77 eV. X-ray diffraction (XRD) results suggested that all films were amorphous in structure at lower substrate temperatures, while crystalline SnO2 films were obtained at higher temperatures. Scanning electron microscopy images showed that the grain size and crystallinity of films depend on the substrate temperature. SnO2 films prepared at 550 °C have a very smooth surface with an RMS roughness of 0.38 nm.