A study of the photoconductivity and thermoelectric properties of SnxSy optical semiconductor thin films deposited by the spray pyrolysis technique

Abstract

In this paper, thin films of tin sulfide (SnxSy) with atomic ratios of y/x=0.25, 0.50, 0.75, 1.00, 1.25 and 1.50 have been prepared on a glass substrate at T=420 °C using the spray pyrolysis technique. The initial materials for the preparation of thin films were an alcoholic solution consisting of tin chloride (SnCl4.5H2O) and thiourea (CS(NH3)2). The prepared thin films were characterized by x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, scanning helium ion microscopy and UV–vis spectroscopy. The photoconductivity and thermoelectric effects of SnxSy thin films have been studied. The SnxSy thin films had a polycrystalline structure with a nearly uniform surface and cluster-type growth. With increasing the atomic ratio of (y/x) in films, the optical gap, photosensitivity, thermal activation energy and Seebeck coefficient changed from 2.72 to 2.37 eV, from 0.05 to 0.78, from 0.07 to 0.48 eV (in the high temperature range) and from +0.17 to −0.22 mV K−1 (at T=350 K), respectively. In addition, the structure of tin sulfide thin films tends to a nearly single-crystal state in (001) preferred orientation corresponding to SnS2 phase with increasing (y/x) ratio. These structure situations considerably influence the photosensitivity and thermoelectric properties of thin films.