A Study on the Structural, Morphological and Optical Properties of Cu_{2-x}Se Thin Films Deposited by Thermal Evaporation

Abstract

In this work, the influence of post-annealing on the structural, morphological, and optical properties of copper selenide thin films deposited on glass substrate by thermal evaporation was investigated in detail. The post- annealing process at different ambient temperatures in a nitrogen atmosphere was applied to thin films deposited at room temperature. The X-ray diffraction (XRD) patterns showed the presence of cubic $Cu_{2-x}Se$ phase, and it was observed that the crystallinity improves with increasing annealing temperature. In addition, it was deduced that the average crystallite size increased with the annealing temperature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to investigate the surface morphology of thin films. It was seen that all samples have compact and densely packed surface morphology and grains on the surface become larger. Surface roughness increased from 11nm to 53 nm as the annealing temperature increased. On the other hand, the optical properties of as-deposited and annealed thin films were investigated by utilizing a UV-Visible spectrophotometer. The direct bandgap energies of as-deposited and annealed samples were estimated to be 2.34 eV, 2.31 eV, and 2.29 eV by using the well-known Tauc relation, respectively. The direct bandgap energy of thin films was also calculated using the derivative spectroscopy technique.