Investigation of the effect of Manganese doping in CdS nanocrystalline thin films

Undoped and Manganese (Mn) doped nanocrystalline cadmium sulphide (CdS) thin films were successfully grown onto indium tin oxide coated glass substrates using an aqueous wet chemical synthetic route. The effect of doping on the structural, optical and morphological properties was investigated using x-ray diffraction (XRD), Raman spectroscopy, Uv-Vis spectroscopy, photoluminescence and atomic force microscopy. XRD spectra revealed a single peak corresponding to (002) plane of hexagonal crystal structure of CdS. The shift in the peak position is also observed in doped samples confirming incorporation of Mn2+ ions into CdS crystal lattice. Photoluminescence emission bands were analyzed for the physical understanding of doping mechanism in CdS lattice. T-4(1) -> (6)A(1) energy transition corresponding to emission band 550 nm is observed. The blue shift observed in absorption spectra in Mn doped sample indicates the decrease in particle size. Raman spectra exhibit two peaks corresponding to longitudinal optical phonon mode (LO) at 298 cm(-1) and its overtone at 594 cm(-1). Mn doped CdS sample shows red shift in the LO peaks representing incorporation of Mn2+ ions into CdS crystal lattice. The increased intensity of LO peak is associated to enhanced coupling between LO phonon and surface plasmon. Uniform, void free adherent nanocrystalline thin films were observed by atomic force microscopy.