Determination and analysis of optical constants for Ge15Se60Bi25 thin films

Thin films of Ge15Se60Bi25 were deposited, at room temperature, on glass substrates by thermal evaporation technique. The optical reflectance and transmittance of amorphous Ge15Se60Bi25 films were measured at normal incident in the wavelength range (500-2500 nm). The optical constants, the refractive index n and the absorption index k, were determined and analyzed according to different approximate methods using the transmittance measurements only and accurate method using the transmittance and reflectance measurements. Analysis of the absorption index k data reveal the values of the optical band gap Egopt, the width of tails Ee and the type of transitions. Some optical parameters such as, high frequency dielectric constant ε∞, dispersion parameters (oscillation energy Es and the dispersion energy Ed), real and imaginary parts of complex dielectric constant (ε1 and ε2) and dielectric parameters (dissipation factor tan δ, dielectric relaxation time τ, the volume and surface energy loss functions) were estimated by analyzing the refractive index n data.The relative errors for all optical parameters depending on different approximate methods were identified and discussed.