Optical properties of amorphous Ge28-xSe72Sbx thin films

Bulk glasses of formal composition Ge_28−xSe₇₂Sb_x with 0≤x≤28 were prepared by applying the quench technique. The optical transmission spectra—using a melt were measured in the range from 200 to 1200 nm for Ge_28−xSe₇₂Sb_x films which are prepared by thermal evaporation technique. A simple, straightforward procedure suggested by Swanepoel, which is based on the use of interference fringes, has been applied to calculate the film thickness. On other hand the driving absorption coefficient (α), consequently the band tail width E_e and the optical band gap have been estimated. The real (ε′) and imaginary parts (ε″) of the dielectric constant have been determined and the optical band gap can also be calculated as a function of imaginary part (ε″). The dispersion parameters such as E₀(single-oscillator energy), E_d (dispersive energy) and M₋₁, M₋₃ (moments) were discussed in terms of the single-oscillator Wemple–DiDomenico model.