Effect of gamma doses on the optical parameters of Se76Te15Sb9 thin films

The effect of γ-radiation dose on the optical spectra and optical energy gap (E_opt.) of Se₇₆Te₁₅Sb₉ thin films was studied. The dependence of the absorption coefficient (α) on the photon energy (hν) was determined as a function of radiation dose. The films show indirect allowed interband transition that is influenced by the radiation dose. Both the optical energy gap and the absorption coefficient were found to be dose dependent. The indirect optical energy gap was found to decrease from 1.257 to 0.664 eV with increasing the radiation dose from 10 to 250 krad, respectively. The results can be discussed on the basis of γ-irradiation-induced defects in the film. The width of the tail of localized states in the band gap (E_e) was evaluated using the Urbach edge method. The refractive index (n) was determined from the analysis of the transmittance and reflectance data. Analysis of the refractive index yields the values of high frequency dielectric constant (ε_∞) and the carrier concentration (N/m^*). The dependence of refractive index on the radiation dose has also been discussed. Other optical parameters such as real and imaginary parts of the dielectric constant (ε₁, ε₂) and the extinction coefficient (k) have been evaluated. It was found that the spectral absorption coefficient is expected to a suitable control parameter of γ-irradiation-sensitive elements of dosimetric systems for high energy ionizing radiation (0.06-1.33 MeV).