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.
