Optical spectroscopy and dispersion parameters of Ge

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 Egopt was allowed indirect transitions. The optical constants such as complex dielectric constant, dispersion parameters (E0 and Ed), ε∞, VELF, SELF and dissipation factor tan δ were determined. It was found that Egopt and the oscillator energy E0 decreased with As addition than Sn addition. Whereas, the Urbach tail energy Ee, the dispersion energy Ed, the real and imaginary dielectric constants ε1 and ε1, the high frequency dielectric constant ε∞ and the dissipation factor tan δ increased with As addition than Sn addition