A new method for calculating the refractive index of semiconductor thin films retrieved from their transmission spectra

• A new method is proposed for calculating the refractive index dispersion of thin film.
• The method calculates the refractive index up to the strong absorption regions.
• The method is successfully applied to ZnO, ZnS, ZnSe, ZnTe, SiO2,As30Se70 thin films.
• The calculated refractive index dispersions agree very well with Swanepoel method.

A simple new method to calculate the refractive index dispersion n(λ) from the transmission spectrum of a semiconductor thin film is presented. The proposed method is based on analyzing the fringes of equal chromatic order (FECO) of thin film by solving the interference equation of light waves interfering coherently at two successive minimum and the one maximum between them. A direct relations for FECO order p, refractive index dispersion n(λ) at each FECO peaks and refractive index variation δn(λ) from one FECO peak to the next one are explicitly obtained. The method of calculation is successively applied to a fixed thickness ZnO, ZnS, ZnSe, ZnTe and SiO2 as well as wedge-shape As30Se70 semiconducting thin films. The obtained refractive index dispersion data for all aforementioned semiconducting thin films agree very well with the previously reported data. In wide wavelength range (500–2500 nm), the obtained refractive index dispersions n(λ) data are fitted to Cauchy dispersion function with relative errors in calculating refractive index of order 5.4 × 10−3 at λ = 800 nm and 5.6 × 10−3 at λ = 2500 nm, respectively. Our calculation procedure yields refractive index data agree very well with the refractive index data calculated from the well known Swanepoel method. Finally, a procedure to calculate the film geometrical thickness t is also presented.