Structural, surface morphological, optical and thermoelectric properties of sol–gel spin coated Zn doped CdS thin films

Abstract

The present work is focussed on Zinc (2, 4, 6, 8 and 10 wt%) doped CdS thin films synthesized by sol–gel spin coating method and deposited on glass substrates. X-ray diffraction patterns of Zn doped CdS thin films exhibit cubic structure. The microstructural properties such as crystallite size, lattice constant, microstrain, dislocation density and stacking fault probability in the films were reported. The surface morphology and topography of the films was studied by using field emission scanning electron microscopy and atomic force microscopy. The incorporation of Zn in CdS and elemental composition of the films has been confirmed with X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). Raman spectrum of Zn doped CdS thin films exhibits 1LO and 2LO phonon modes. The optical band gap of CdS thin films increased from 2.63 to 2.73 eV with the increase of Zn dopant from 2 to 10%. Thermoelectric power measurements show negative Seebeck coefficient indicating n-type semiconducting behaviour. The carrier concentration of Zn doped CdS thin films at room temperature are found to be in the range of 1019–1020 cm−3 suggesting that the prepared films are degenerate semiconductors. The increase in thermal conductivity of Zn doped CdS thin film is due to the increase in carrier concentration of the films. The lattice thermal conductivity of Zn doped CdS thin films had an inverse temperature dependent and at high temperatures shows the dominance of phonon scattering.