Modification of structure, electrical, linear and third-order nonlinear optical properties of spray pyrolyzed tin oxide films by deposition temperature

Highly transparent and conducting polycrystalline n-type SnO₂ thin films with prominent peak corresponding to (1 1 0) plane was deposited using the simple spray pyrolysis technique. A systematic investigation was carried out in order to understand the influence of deposition temperature on the structure, surface morphology, composition, linear and third-order nonlinear optical (NLO) properties, photoluminescence and electrical characteristic of the deposited films. The rise in the deposition temperature led to increase in crystallinity and transmittance of the films. The films deposited at 450 °C showed the highest crystallite size, lesser dislocation density and fibrous surface morphology. The films deposited at 450 °C showed the highest transmittance of around 90% in the visible region and a direct energy band gap of 3.9 eV. Increase in the deposition temperature also reduced the film resistivity and enhanced the carrier concentration. The film deposited at 450 °C possessed the maximum carrier concentration of 2.04 × 10²⁰ cm⁻³ and minimum resistivity of 0.2483 Ω cm. It was also observed that the deposition temperature influenced on photoluminescent emission and the third-order nonlinear properties of the films. The photoluminescence spectra analysis of the deposited films indicated the existence of oxygen vacancies and other defects which led to nearly a white light emission. The film deposited at 450 °C showed a nonlinear absorption coefficient, nonlinear refractive index and susceptibility of 0.72 cm/W, 5.74 × 10⁻³ cm²/W and 7.29 × 10⁻³ esu, respectively. These films exhibited optical limiting behaviour and the obtained least limiting threshold was 1.1 kJ/cm². The results clearly showed the applicability of spray pyrolyzed SnO₂ thin films deposited at 450 °C in optoelectronic and nonlinear devices.