Influence of cadmium concentration on the optical and structural properties of cadmium selenide thin films

Abstract

Thin films of cadmium selenide (CdSe) and CdxSe100−x (x=54, 34) have been deposited by vacuum evaporation onto ultraclean glass substrates at room temperature from as-prepared powders. Fabricated samples were characterized using X-ray diffraction (XRD), UV–vis and Fourier transform infrared (FTIR) spectroscopy. XRD indicated the formation of polycrystalline CdxSe100−x thin films polycrystalline in nature with the preferred orientation along the (002) plane. The crystallite sizes of thin films calculated by the Scherer formula were found to be in the range of 29–82nm. The crystallinity of thin films degraded on increasing the Cd concentration in the Cd–Se system. The band gaps of thin films were obtained from their optical absorption spectra, which were found in the range of 1.69–2.20eV. The band gap of the Cd34Se66 thin films was found to be very high because of the decrease of their crystallites sizes in comparison to the CdSe and Cd54Se46 thin films. From the FTIR spectra it was revealed that the Cd–Se peaks shifted to lower wavelengths with increase in selenium concentration. The SEM measurements for CdSe, Cd54Se46 and Cd34Se66 thin films reveal that the particle size and the crystalline nature decreased when Se content increased in the system.