These defects are responsible for the presence of localized states in the amorphous band gap. Therefore, these unsaturated bonds result in the formation of defects in the presently studied thin films containing aligned nanorods, thereby producing a large AZD2014 molecular weight number of localized/defect states in the present system. Tellurium
glass contains short chains, whereas selenium glass contains ARRY-438162 datasheet long chains and selenium rings. As Se concentration increases or Te concentration decreases, the number of Se rings increases and the number of long Se-Te polymeric chains and Se-Te mixed rings decreases . Therefore, the addition of selenium to tellurium increases the number of defect states, which increases further with the increase in Se concentration. As these defect states are also associated with unsaturated bonds formed during the deposition of these thin films, we may state that the number of unsaturated bonds increases with the increase in Se concentration. This increase in the defect states or unsaturated bonds with the concentration of Se results in the narrowing of optical band gap. Therefore, the optical band gap in the present system decreases with the increase in Se concentration. We can also interpret this decrease in optical band gap with respect
to the shift in Fermi click here level. The position of Fermi level in such systems is determined
by the distribution ID-8 of electrons over the localized states . For the present system of a-Se x Te100-x thin films containing aligned nanorods, we use the following relation to estimate the values of extinction coefficient (k). This relation is given as (5) We use the theory of reflectivity of light to estimate the values of refractive index (n) and extinction coefficient (k) for the present system. Employing this theory, the reflectance of light from a thin film can be written in terms of Fresnel’s coefficient. Therefore, the reflectivity on an interface can be expressed by the following relation [36–38]: (6) Where λ is the wavelength of the incident light and α is the absorption coefficient. The dependence of incident photonic energy on the extinction coefficient (k) for Se x Te100-x thin films containing aligned nanorods is shown in Figure 6. It is observed that the value of extinction coefficient shows an overall decreasing trend with the increase in photon energy. Figure 7 presents the variation of refractive index (n) with the photon energy. From this figure, an increase in the value of refractive index with the increase in photon energy is observed. These results are in close agreement with the results reported by various workers [18, 39]. The calculated values of n and k for different compositions of Se are shown in Table 1.