Influence of isochronal heat treatment on spray-deposited mixed phase tin based thin films for ammonia gas sensor applications

Abstract

The current work applied the spray pyrolysis (SP) approach to coat mixed-phase SnS thin films at 350 °C, and then air annealed at 400,450,500 °C for use in sensor and solar cells applications. A variety of methods were employed to evaluate the structural, morphological, compositional, optical, and electrical characteristics of synthesised mixed-phase films. Films annealed at 500 °C are reported to have bigger crystal sizes, and all deposited SnS films exhibit the orthorhombic phase in addition to tetragonal phase of SnO2, with other visible secondary phases like SnS2,Sn2S3. Fourier transform infrared spectroscopy and Raman analyses verified the molecular structure and vibrational mode of SnS films. The Scanning electron microscopy tests reveal a consistent, size-varying two-dimensional flake like grain structure, while the optical studies show a variation in optical direct band-gap from 1.79 to 2.75eV. The Hall-effect shows that films subsequently annealed at 400 °C have improved electrical properties. An efficient metal oxide semiconductor gas sensor was developed by applying mixed-SnS film on the conducting side of an indium tin oxide coated glass plate. To examine the sensor selectivity at room temperature, a variety of test gases, such as NO2, H2S, C2H5OH, NH3, were purged at different concentrations. The optimum working temperature and concentration for NH3 selective gas have been determined to be 350 °C and 5 ppm. The sensor sensitivity is found to be maximum at operating temperature of 200 °C towards NH3 gas. An inexpensive, fabricated MOS-gas sensor based on mixed-phase SnS can be easily mass produced and may find potential applications in industrial and environmental monitoring.

Keywords

• Spray pyrolysis
• Mixed SnS phase
• Isochronal treatment
• MOS
• Ammonia gas sensor