Effect of Sb addition on linear and non-linear optical properties of amorphous Ge–Se–Sn thin films

• The optical characterization of thin films of Ge20Sn10Se70−xSbx (x = 0, 3, 6, 9, 12, 15 at.%) amorphous C.G. system has been carried out by using transmission spectra.
• Refractive index is found to be increasing with increase in Sb concentration. This can be attributed to the increase in polarisability of the atoms.
• The decrease in extinction coefficient with the increase in wavelength implies that the absorption losses decreases and the specimen is transparent for higher wavelengths.
• Increase in optical conductivity with energy is observed which is due to increase in refractive index and absorption coefficient.
• Non-linear susceptibility and non-linear refractive index are found to be increasing with the increasing concentration of Sb which implies that the specimen is diffraction free and thus have practical applications in photonic technology.

Optical characterization of amorphous thin films of Ge20Sn10Se70−xSbx (x = 0, 3, 6, 9, 12, 15) has been carried out. Thin films were deposited onto pre cleaned glass substrates using thermal evaporation technique. Transmission spectra of the films were recorded, for normal incidence, in range 400–2400 nm. Refractive index of the films was calculated using the envelope method by Swanepoel. Dispersion analysis has been carried out using single effective oscillator model. Other optical constants such as absorption coefficients, extinction coefficients have also been evaluated. Tauc plots were used to evaluate the optical band gap. The refractive index has been found to be increasing while the band gap decreases with increasing Sb concentration. The observed optical behavior of the films has been explained using chemical bond approach. Cohesive energy is found to be decreasing in the present work, which reflects that bond strength decreases with the increasing content of Sb. Non-linear optical parameters (i.e. n2 and χ(3)) have been derived from linear optical parameters (i.e. n, k, Eg). Observed changes in linear and non-linear parameters have been reported in this study.