Effect of sulfurization on physical and electrical properties of MoS2 films synthesized by electrodeposition route

Abstract

Thin films of uniform molybdenum disulphide (MoS2) were produced on conducting glass (FTO) using the electrochemical route from aqueous solution (NH4)2MoS4 then subjected to annealing treatment under argon gas with and without sulfur. The influence of sulfurazation on the structural, morphological, optical, and electrical properties of samples was investigated. Scanning electron microscopy exhibits homogeneous surface of the samples. Furthermore, the sample exposed to sulfur treatment has narrower grains comparing with that annealed without sulfur. Energy dispersive x-ray spectroscopy (EDX) confirmed the existence of the MoS2 films with a 2.1 S/Mo atomic ratio for the samples heated with sulfur and a 1.76 atomic ratio for those annealed without sulfur. Our results showed that the type of conduction (n or p) have been found to be sensitive to the S/Mo ratio. In fact, an excess of sulfur anions induces a p-type conductivity while a lack of sulfur results an n-type conductivity. X-ray diffraction showed that with sulfuration, the (002) plan main peak is shifted to smaller angle. This is in direct relation to the stress due to the excess of sulfur. As a fact, sample with grater grain size (D) shows the lowest microstrain (ε) and dislocation density (δ). Moreover, the band gap energy values confirmed the results found in fact, referring to the UV–vis diffuse reflectivity spectra, the band gap energy value of the thin films with lack of sulfur was 1.76 eV and 1.66 eV for those annealed with sulfur. In addition, according to the Mott–Schottky plots we confirmed that the films treated without sulfur show n-type conductivity with a carrier density of 3.24 × 1022 cm−3 and a flat-band potential of −0.66V. However, the films annealed with sulfur showed a p-type semiconductor character with a 1.46 × 1022 cm−3 carrier density and a −0.24 V flat-band potential.