Optical red shift spectra in CuxGe32S68-x films for infrared and solar cell window applications

Abstract

The physical characteristics of Cu-doped ternary glasses have been analyzed. The CuxGe32S68 − x (x = 0.0, 4.0, 7.0, 10.0 and 13.0 at.%) chalcogenide alloys have been manufactured by the conventional melt quenching method. The glass densities (ρ) increase with the Cu amounts, whereas the main atomic volume (Vm) decreases. Transmission and reflectance were measured in the wavelength range of 0.35–2.5 μm. The generated envelops (RM and Rm) of reflectance spectra were used to calculate the film thickness (t), the refractive index (n), and the extinction coefficient (k). With the increase in Cu contents from 0.0 to 13.0 at.%., the n values increased from 2.07 to 2.43, whereas the optical gap (Eg) decreased from 2.81 eV to 2.42 eV. The obtained results were explained in terms of electronic polarizability, plasma frequency, metallization parameter, and refraction losses, which have been calculated to understand the need for amorphous chalcogenide compositions that can be applied for optical device purposes. The effect of Cu content on the non-linear index of refraction (n2) and third-order susceptibility (χ (3)) has been studied. The value of n2 increased from 13.88 × 10−12 to 60.2 × 10−12 esu, whereas the value of χ (3) rose from 7.6 × 10−11 to 38.83 × 10−13 esu with the addition of denser and higher atomic radius elements Cu in the CGS system. Overall, the composition of Cu13Ge32S55 is suitable, as all-optical parameters show the maximum values that can be used for optical device purposes.