Structure and optical properties of CuAl$S _2$ thin films prepared via chemical bath deposition

CuAl$S _2$ thin films of thicknesses 118 ± 5 nm were deposited on glass substrates using chemical bath deposition technique. The details of the preparation method are well described. The method is relatively simple and is easily controlled and sufficient to produce large area and good adherence to the substrate films. Effect of annealing temperature Ta on the structure, and optical properties of CuAl$S _2$ films were investigated. The structures of the films were studied by X-ray diffraction and FTIR spectrophotometer. The optical properties of the films were ascertained by UV-VIS spectrophotometer (wavelengths ranging between 300 and 900 nm). The optical transmittance and absorption were utilized to compute the absorption coefficient, band gap energy and optical constant of the films. Nature of the optical transition of the films has been observed in direct allowed with band gap energies between 2.81 eV and 2.4 eV depending on annealing temperatures. The refractive index and extinction coefficient behavior were found to very affect by annealing temperature.