Enhancement in microstructural and optical properties of thermally evaporated CdTe/CdSe heterojunction thin Films

Abstract

The optimization of microstructural and optical properties of a thin layer is an important step prior device fabrication process, so an enhancement in these properties of thermally evaporated CdTe/CdSe thin films was reported in this work. We choose to research (CdSe) materials as a n-type absorber layer in the CdTe/CdSe heterojunction thin film. The Effect of annealing temperature on the structural and optical properties of CdTe/CdSe Heterojunction thin films was studied, using various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and Double-beam computer-controlled spectrophotometer in the wavelength between 200 nm and 2500 nm. Diffraction (XRD) patterns showed that the as-prepared films were amorphous nature, whereas the annealed films were polycrystalline. These results were confirmed by scanning electron microscopy investigations. It was found that the crystallite size and degree of crystallinity of the studied films depend on the annealing temperature. Furthermore the optical measurement shows that this treatment shifts the optical absorption edge at low energy and decreases the optical band gap from 1.92 eV, to 1.37eV while the values Urbach energy increase as the annealing temperature increased from 300 K to 433 K. As consequence is that the heat treatment improves the quality of the CdTe/CdSe heterojunction thin films for the potential use in photovoltaic applications.