Synthesis and characterization of Bix(Se80Te20)100−x amorphous thin films

In this study, amorphous Bix(Se80Te20)100−x glasses with (0 ≤ x ≤ 12) were prepared by the usual melt quench technique. Thin films of these glasses were deposited onto glass substrates by using thermal evaporation method. The amorphous nature of the as-prepared films was confirmed by X-ray diffraction. Structural investigations were performed using X-ray energy-dispersive spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. The transmission spectra of these films were measured at normal incidence in the wavelength range 400–2500 nm. Swanepoel’s analysis of the maxima and minima of the interference fringes was used to determine the film thickness, the complex index of refraction and the extinction coefficient with high accuracy. The dispersion of the refractive index was well discussed in terms of the single oscillator model (Wemple and DiDomenico). It was found that increasing Bi content led to the increase in refractive index and the extinction coefficient of the Bix(Se80Te20)100−x films, while the optical band gap decreased. The mechanism of the optical absorption in Bix(Se80Te20)100−x films obeyed the allowed indirect optical transition. The decrease in optical gap with increasing Bi content was discussed in terms of the chemical bond approach.