Abstract
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−
x
Te
4Ag
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.