Optical band gap, refractive index dispersion and single-oscillator parameters of amorphous Se70S30−xSbx semiconductor thin films

The optical band gap, refractive index and oscillator parameters of amorphous semiconductor Se70S30− x Sb x thin films with x = 0, 18, 12 and 30 at. % deposited by electron-beam evaporation were investigated by optical spectrophotometry. The energy gap decreases from 2.25 to 1.08 eV with increasing Sb content introduced at the expense of S, which is explained in terms of chemical bond and cohesive energy approaches. The method proposed by Swanepoel is applied to extract the refractive index n. It was found that the refractive index is strongly related to the change in the concentration of Sb, which is related to the increase density of the film material with increasing Sb content, and is interpreted in terms of polarisability and the mean coordination number. The ratio of the refractive indices of (Se70Sb30)/(Se70S30) is ≈ 1.32 at a wavelength λ ≈ 1600 nm and increases to 1.48 at λ ≈ 950 nm. Such a refractive index contrast could be used to fabricate a distributed Bragg reflector (DBR) stack with limited ...