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

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 SnO 2 , with other visible secondary phases like SnS 2 ,Sn 2 S 3 . 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 NO 2 , H 2 S, C 2 H 5 OH, NH 3 , were purged at different concentrations. The optimum working temperature and concentration for NH 3 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 NH 3 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.