Optical properties of a-(Se70Te30)100−x(Se98 Bi2)x thin films

Abstract Measurements of optical constants (absorption coefficient, refractive index, extinction coefficient, real and imaginary part of the dielectric constant) have been made on a-(Se 70 Te 30 ) 100− x (Se 98 Bi 2 ) x thin films (where x =0, 5, 10, 15 and 20) of thickness 2000 A in the wavelength range 450–1000 nm. It is found that the optical bandgap decreases with the increase of Se 98 Bi 2 concentration in the a-(Se 70 Te 30 ) 100− x (Se 98 Bi 2 ) x system. The value of refractive index ( n ) decreases, while the extinction coefficient ( k ) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states varying effective Fermi level.