Different compositions of Bi5GexSe95
x (x ¼ 30, 35, 40 and 45 at %) thin films were deposited onto
cleaned glass substrates by thermal evaporation method. The structural characterization revealed that,
the as-prepared films of x ¼ 30, 35 and 40 at. % are in amorphous state but there are few tiny crystalline
peaks of relatively low intensity for the film with x ¼ 45 at. %. The chemical composition of the asprepared
Bi5GexSe65
x films has been checked using energy dispersive X-ray spectroscopy (EDX). The
optical properties for the as-deposited Bi5GexSe65
x thin films have been studied. The additions of Ge
content were found to affect the optical constants (refractive index, n and the extinction coefficient, k).
Tauc’s relation for the allowed indirect transition is successfully describing the mechanism of the optical
absorption. It was found that, the optical energy gap (Eg) decreases with the increase in Ge content. These
obtained results were discussed in terms of the chemical bond approach proposed by Bicermo and
Ovshinsky. The composition dependence of the refractive index was discussed in terms of the single
oscillator model.