Structural, optical and electrical properties studies of ultrasonically deposited tin oxide (SnO2) thin films with different substrate temperatures

Abstract

Undoped thin films of tin oxide (SnO2) were deposited onto microscopic glass substrates using an ultrasonic spray pyrolysis technique. The thin films were deposited on glass at large scale of temperature ranged in 400–500°C and stepped by 20°C. The effect of substrate temperature on structural, electrical and optical properties was studied using X-ray diffraction (XRD), UV–visible spectrophotometer and a conventional four point probe technique. XRD showed that all the films were polycrystalline with major reflex along (110) plane, manifested with amelioration of grain size from 6.51 to 29.80nm upon increasing substrate temperature. Lattice constant ‘a’, ‘c’, microstrains and dislocation densities were affected by the substrate temperature. Transmittance of about 75% at more than 800nm for films prepared at 480°C has been observed. With increasing the substrate temperature the direct band gap energy was averaged in 4.03–4.133eV. Plasma frequency (ωp) was estimated to be 4⋅1014Hz and optically estimated free electrons number N leading to predict that, in SnO2 material, the effective density of conduction band states is about 5⋅1019cm−3. Among all the samples the film that deposited at 480°C exhibited lowest resistivity of about 9.19×10−3Ωcm.