Validity of Swanepoel's Method for Calculating the Optical Constants of Thick Films

Optical constants, dispersion and oscillator parameters of dierent thicknesses of amorphous Ge25Cd5Se70 lms have been deposited onto glass substrates using thermal evaporation technique.The optical constants have been investigated by optical spectrophotometry measurements.The straight forward analysis proposed by Swanepoel, which is based on the use of the extremes of the interference fringes has been used in order to derive the refractive index and the lm thickness in µm range.The refractive index could be extrapolated by the Cauchy dispersion relationship over the whole spectral range, which extended from 400 to 2500 nm.It is observed that, refractive index n increases with the lm thickness.The possible optical transition is found to be allowed indirect transition with energy gap increase from 1.915 to 1.975 eV with increasing lm thickness.The dispersion of the refractive index is discussed in terms of the WempleDiDomenico single oscillator model.The interband oscillator wavelength, the average oscillator strength, and the optical conductivity were estimated for dierent thicknesses of amorphous Ge25Cd5Se70 lms.