Effect of substrate temperature on the structural and electrical properties of spray deposited lead sulfide thin films

Abstract

Lead sulfide (PbS) thin films were prepared by chemical spray pyrolysis method using lead acetate and thiourea as precursors of Pb+2 and S-2 ions. X-ray diffraction (XRD) technique, scanning electron microscope (SEM) and EDAX analysis were used for structural, morphological and compositional characterization. XRD analysis shows that the films are cubic in nature with a preferred orientation along (2 0 0). EDAX analysis shows that films deposited at 150°C are sulfur rich. An increase in the substrate temperature results in a decrease in the sulfur content of the prepared film. It has been observed that thin films deposited at or above 225°C are smooth & uniform morphologically. Beyond a substrate temperature of 275°C, the films become discontinuous and non-uniform. However, the films are sulfur rich, even at 275°C. Electrical conductivity of prepared thin films have been measured using silver contacts in coplanar geometry. Films are n - type as confirmed by hot probe technique. The electrical conductivity at room temperature (25°C) was in the order of 10-4 Ω-1cm-1 and was found to increase with increase in temperature showing the semiconducting nature of the films with the band gap of 0.39 eV.