Characterization of Pure and Al-Zn Doped Conducting SnO2 Thin Films for Gas Sensors

Abstract

The present study investigates the influence of Al–Zn co-doping on the structural, morphological, and optical properties of nanostructured SnO2 thin films prepared by spray pyrolysis. Pure and 2 mol% Al–Zn co-doped SnO2 thin films were deposited on glass substrates at 500 °C using a laboratory-developed spray pyrolysis system. Tin chloride pentahydrate (SnCl2•5H2O) was used as the precursor, while aluminum chloride and zinc chloride were employed as dopant sources. The precursor solution was prepared in ethanol and stirred continuously at 50 °C for 4 h. During deposition, the spray nozzle was maintained at a distance of 25 cm from the substrate and the solution was delivered at a spray rate of 10 mL min¹. The films were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), UV–Visible spectroscopy, and energy-dispersive X-ray analysis (EDAX). XRD analysis showed that the average crystallite size decreased from 38.2 nm for the undoped SnO2 film to 27.3 nm for the Al–Zn co-doped film. The optical band gap decreased from 3.52 eV to 3.47 eV after co-doping, while good visible-region optical transparency was retained. EDAX confirmed the presence of the intended dopant elements in the co-doped film. These results demonstrate that Al–Zn co-doping modifies the structural and optical properties of SnO2 thin films and indicates their potential for gas sensor applications. Future studies will investigate gas-sensing response, sensitivity, selectivity, response/recovery characteristics, and long-term stability under different operating temperatures, humidity levels, gas concentrations, and interfering-gas conditions.