Optical properties of amorphous CuS thin films deposited chemically at different pH values

Amorphous copper sulfide thin films were deposited on commercial glass substrates at room temperature by chemical bath deposition. The effect of the pH value of the chemical bath on the optical properties of the amorphous thin films is investigated and discussed. The influence of the pH value of the chemical bath was examined by means of the optical transmission of the thin films in the wavelength range of 300–1100 nm taken at room temperature. Next, using these data, the absorption coefficient, the optical band gap value, the extinction coefficient, the refractive index, and the real and imaginary parts of the dielectric constant were calculated. The dispersion of the refractive index of the thin films was also investigated in terms of the single-oscillator Wemple and DiDomenico method. The value of the optical band gap determined by Tauc's extrapolation was found to be equal to one and half times the oscillator energy values of all deposited films.

► Amorphous CuS films were deposited at 40 °C for 24 h by chemical bath deposition. ► The pH of the chemical bath adjusted to 1.7, 1.8, 1.9, 2.01 and 2.19. ► Effects of pH on structural and optical properties of CuS films were investigated. ► Refractive index, extinction and dielectric coefficients were calculated. ► Optical band gap of amorphous CuS thin films was changed in the range 2.13–2.35 eV.