Optical spectroscopy, optical conductivity, dielectric properties and new methods for determining the gap states of CuSe thin films

The paper describes the structural and optical properties of CuSe thin films. X-ray diffraction pattern indicates that CuSe thin film has an amorphous structure. Transmittance T(λ) and reflectance R(λ) measurements in the wavelength range (300–1700 nm) were used to calculate the refractive index n(λ), the absorption index and the optical dispersion parameters according to Wemple and Didomenico WDD model. The dispersion curve of the refractive index shows an anomalous dispersion in the absorption region and a normal dispersion in the transparent region. The optical bandgap has been estimated and confirmed by four different methods. The value for the direct bandgap for the as-deposited CuSe thin film approximately equals 2.7 eV. The Raman spectroscopy was used to identify and quantify the individual phases presented in the CuSe films.

Research highlights▶ The structural, optical dispersion parameters and the Raman spectroscopy have been studied for CuSe thin films. ▶ X-ray diffraction results indicate the amorphous nature of the thermally evaporated CuSe thin films. ▶ The refractive index shows an anomalous dispersion at the lower wavelength (absorption region) and a normal dispersion at the higher wavelengths (transparent region). ▶ The refractive index dispersion obeys the single oscillator model proposed by Wemple and DiDomenico WDD model and the single oscillator parameters were determined. ▶ The band gap of CuSe thin films was determined by three novel methods i.e. (relaxation time, real and imaginary dielectric constant and real and imaginary optical conductivity) which in a good agreement with the Tauc band gap value.