Optical spectroscopy and dispersion parameters of Ge15Se60X25 (X = As or Sn) amorphous thin films

In the present work the optical properties of Ge15Se60X25 (X = As or Sn) films have been studied. Optical reflectance and transmittance of films were obtained at normal incident in the wavelength range (500-2500 nm). The transmittance measurements were used to calculate the refractive index n and the absorption index k depending on Swanepole's method. The analysis of the optical absorption data revealed that the optical band gap E-g(opt) was allowed indirect transitions. The optical constants such as complex dielectric constant, dispersion parameters (E-0 and E-d), epsilon(infinity), VELF, SELF and dissipation factor tan delta were determined. It was found that E-g(opt) and the oscillator energy E-0 decreased with As addition than Sn addition. Whereas, the Urbach tail energy E-e, the dispersion energy E-d, the real and imaginary dielectric constants epsilon(1) and epsilon(2), the high frequency dielectric constant epsilon(infinity) and the dissipation factor tan delta increased with As addition than Sn addition.