Investigations on structural, vibrational, morphological and optical properties of CdS and CdS/Co films by ultrasonic spray pyrolysis

CdS and CdS/Co films have been deposited on glass substrates by an ultrasonic spray pyrolysis method. The effects of Co incorporation on the structural, optical, morphological, elemental and vibrational properties of these films were investigated. XRD analysis confirmed the hexagonal wurtzite structure of all films and had no impurity phase. While CdS film has (0 0 2) as the preferred orientation, CdS/Co films have (1 1 0) as the preferred orientation. The direct optical band gap was found to decrease from 2.42 to 2.39 eV by Co incorporation. The decrease of the direct energy gaps by increasing Co contents is mainly due to the sp-d exchange interaction between the localized d-electrons of Co2+ ions and band electrons of CdS. After the optical investigations, it was seen that the transmittance of CdS films decreased by Co content. The Raman measurements revealed two peaks corresponding to the 1LO and 2LO modes of hexagonal CdS. The vibrational modes of Cd-S were obtained in the wavenumber range (590-715 cm−1) using Fourier transform infrared spectroscopy (FTIR). The elemental analysis of the film was done by energy dispersive X-ray spectrometry.

The CdS film has an average transmittance of 77%, whereas the CdS/Co films show an average transmittance above 64%. As the Co content increases beyond this, the average transmittance decreases. Four characteristic optical absorption bands in the visible range labelled as 1, 2, 3 and 4 can also be observed. These four absorption edges correspond to 680 nm (1.82 eV), 690 (1.79 eV), 720 nm (1.72 eV) and 740 nm (1.67 eV), respectively.Highlights► We have studied the structural (XRD), optical (UV-vis), morphological (AFM), elemental (EDS) and vibrational (FT-IR and Raman) properties of CdS and CdS/Co films deposited by ultrasonic spray pyrolysis method. ► X-ray diffraction analysis showed that the preferential orientation of the films shifts from H(0 0 2) to H(1 1 0) with Co content. ► Raman and FT-IR spectra show the change in the peak intensity with increasing Co concentration.