Derivation of the optical constants of thermally-evaporated uniform films of binary chalcogenide glasses using only their reflection spectra

Optical reflection spectra, at normal incidence, of binary chalcogenide glass thin films of chemical compositions As25S75 and Ge33Se67 deposited by thermal evaporation, were obtained in the 400 nm to 2200 nm spectral region. The optical constants of these particular amorphous materials were accurately determined using an optical characterization method proposed by Minkov, based on the maximum and minimum envelopes of the reflection spectrum, which allows to obtain both the real and the imaginary parts of the complex refractive index, and the film thickness. The dispersion of n is discussed in terms of the single-oscillator Wemple-DiDomenico model. The optical gap has been determined from the absorption coefficient values by Tauc's procedure. (C) 1998 Elsevier Science S.A.