Characterization of CoS and Co1-xCdxS thin films deposited by spray pyrolysis technique

Abstract

Pure cobalt sulfide (CoS) and cadmium (Cd) doped CoS (Co1-xCdxS) thin films with different values of x (viz, 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were deposited on glass substrate from aqueous solutions of Co(CH3COO)2.4H2O, Cd(CH3COO)2.3H2O and NH2CSNH2 at 523 K using a low cost spray pyrolysis technique. The surface morphology, elemental, structural, optical and electrical properties of the asdeposited films were studied by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), UV-Visible spectroscopy and van-der Pauw method respectively. The Co0.8Cd0.2S film was annealed at 673, 773, and 873 K for one hour. The surface morphology of the as-deposited Co1-xCdxS films was found to be inhomogeneous and the film became homogenous after annealing. With the increase of annealing temperature the defects and surface roughness of the film was reduced. The elemental compositions revealed the presence of Co, S and Cd in the film. The XRD analysis showed that as-deposited films were amorphous and the formation of crystalline nature of the film was started after annealing. The absorption coefficient, optical band gap, refractive index, extinction coefficient, optical conductivity and dielectric constant of the films were calculated from UV-VIS spectroscopy analysis. The optical band gap of the as-deposited Co1-xCdxS films was increased from 2.2 to 3.10 eV with increasing Cd content from x = 0.0 to 1.0. This indicated that the presence of Cd in the system greatly affected the optical band gap. The optical band gap of annealed Co0.8Cd0.2S films also increased from 3.25 to 3.45 eV with the increase of annealing temperature. The increase of electrical conductivity with the increase of temperature indicated semiconducting behavior of the as-deposited films. Activation energy of Co1-xCdxS films increased between 0.25 to 0.50 eV with the increase of Cd in the solution.