Optical band gap and optical constants in amorphous Se96−xTe4Agx thin films

The optical constants (absorption coefficient (α), refractive index (n), extinction coefficient (k), real and imaginary part of dielectric constant) have been studied for a-Se_96−xTe₄Ag_x (where x=0, 4, 8, 12) thin films as a function of photon energy in the wavelength range (500-1000 nm). It has been found that the optical band gap increases while n and k decreases on incorporation of Ag in Se-Te system. The value of α and k increases, while the value of n decreases with incident photon energy. The results are interpreted in terms of the change in concentration of localized states due to the shift in fermi level. A correlation between the optical band gap and electronegativity of the alloys indicates that the optical band gap increases with the decrease of electronegativity.