Improvement of Swanepoel method for deriving the thickness and the optical properties of chalcogenide thin films.

A tangencypoint method (TPM) is presented to derive the thickness and optical constants of chalcogenide thin films from their transmission spectra. It solves the problem of the abnormal value of thickness in the strong absorption region obtained by Swanepoel method. The accuracy of the thickness and refractive index is better than 0.5% by using this method. Moreover, comparing with Swanepoel method by using the same simulation and experimental data from the transmission spectrum, the accuracy of the thickness and refractive index obtained by the TPM is higher in the strong absorption region. Finally the dispersion and absorption coefficient of the chalcogenide films are obtained based on the experimental data of the transmission spectrum by using the TPM.