Extent of dependence of crystalline, morphological, optical and electrical properties on deposition time of sprayed SnS thin films

In the present experimental work, Tin Sulphide (SnS) thin films with various thicknesses have been grown on nonconducting substrate by using chemical spray pyrolysis technique in order to study the extent of dependence of crystallite size, morphological and optical properties of SnS films on their deposition times. The obtained films were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible and Hall Effect measurements. From 15 min to 60 min with an increase of 15 min each time one of all films was deposited, the XRD analysis indicated that all four sprayed SnS films are mainly composed with orthorhombic SnS phase, having a growing dominant peak intensity (120), with increasing deposition time. In addition, the XRD revealed the presence of the Sn2S3 secondary phase in SnS film sprayed at the longest time (60 min). It was found that the measurements of crystallite size and microstrain are varied in the inverse manner throughout the deposition period. The SEM and AFM analysis revealed that the morphology of sprayed films have good surface coverage without pinholes or cracks. AFM analysis confirmed that the root-mean-square (RMS) roughness behavior of the sprayed films increases from 14.6 to 56.7 nm with increasing deposition time. Optical studies showed that the transmittance decreases with the deposition time increase, and the minimum value of Urbach energy was 360 meV for the film deposited at 45 min, showing an improvement of the SnS film crystallinity. In addition, the optical band gap values significantly increased from 0.69 to 2.10 eV by increasing the deposition time from 15 min to 60 min. The Hall Effect study showed that SnS thin films have p-type conductivity. The lowest resistivity and higher carrier concentration were found to be 0.134 Ω cm and 8.15 × 10¹⁹ (ion/cm^-3 ), respectively. These obtained results revealed that the deposition time interestingly affect the properties of sprayed SnS films, which would qualifying them to meet the requirements to be serve in different applications.

Defect-Induced Gas-Sensing Properties of a Flexible SnS Sensor under UV Illumination at Room Temperature

Tin sulfide (SnS) is known for its effective gas-detecting ability at low temperatures. However, the development of a portable and flexible SnS sensor is hindered by its high resistance, low response, and long recovery time. Like other chalcogenides, the electronic and gas-sensing properties of SnS strongly depend on its surface defects. Therefore, understanding the effects of its surface defects on its electronic and gas-sensing properties is a key factor in developing low-temperature SnS gas sensors. Herein, using thin SnS films annealed at different temperatures, we demonstrate that SnS exhibits n-type semiconducting behavior upon the appearance of S vacancies. Furthermore, the presence of S vacancies imparts the n-type SnS sensor with better sensing performance under UV illumination at room temperature (25 °C) than that of a p-type SnS sensor. These results are thoroughly investigated using various experimental analysis techniques and theoretical calculations using density functional theory. In addition, n-type SnS deposited on a polyimide substrate can be used to fabricate high-stability flexible sensors, which can be further developed for real applications.