Chalcogenide Te40Se30S30 thin films of different
thickness (100–450 nm) are prepared by thermal
evaporation of the Te40Se30S30 bulk. X-ray examination of
the film shows some prominent peaks relate to crystalline
phases indicating the crystallization process. The calculated
particles of crystals from the X-ray diffraction peaks
are found to be from 11 to 26 nm. As the thickness
increases, the transmittance decreases and the reflectance
increases. This could be attributed to the increment of the
absorption of photons as more states will be available for
absorbance in the case of thicker films. The decrease in the
direct band gap with thickness is accompanied with an
increase in energy of localized states. The obtained data for
the refractive index could be fit to the dispersion model
based on the single oscillator equation. The single-oscillator
energy decreases, while the dispersion energy
increases as the thickness increases.