Structural, electrical and optical studies on spray deposited Cadmium Sulphide and Copper Indium Disulphide thin films

摘要

CdS and CuInS2 thin films are deposited by spray pyrolysis technique. CdS thin films are deposited from the aqueous solution of cadmium chloride and thiourea with [Cd]/[S] ratio =1 on glass and ITO coated glass substrates at temperature of about 4000C. CuInS2 thin films are deposited on glass substrates at 350oC from the aqueous solutions of copper chloride, indium chloride and thiourea with [Cu]/[In] ratio =1.1 and [Cu]/[In] ratio =1.25. The ratio of [S]/[Cu] = 3.5 in both the cases. X-ray diffraction shows that the films are polycrystalline in nature. The grain size and strain in the films are calculated from XRD. Surface morphology of the deposited films is observed by SEM. Hot probe method is used to determine the conductivity type of the films. Resistivity of the films is determined by van der Pauw method. Resistivity of all the films is in the order of 10-2 ohm-cm. Thickness and refractive index of the thin films is measured using an Ellipsometer. UV-Vis analysis is carried out to measure the energy gap of the films. The bandgap of 2.43eV and ~1.48eV is obtained for CdS and CuInS2 thin films, respectively. The CdS film shows absorption coefficient (α) of about 2 x 104 cm–1 near the absorption edge. All the CdS films have transparency of about 70% in the wavelength range of 510nm – 800nm. The CuInS2 films have absorption coefficient (α) in the order of 104 cm–1 in the visible and red region of the absorption spectra.