Optical properties of a-(Se70Te30)(100-x)(Se-98 Bi-2)(x) thin films

Measurements of optical constants (absorption coefficient, refractive index , extinction coefficient, real and imaginary part of the dielectric constan t) have been made on a-(Se70Te30)(100-x) (Se98Bi2)(x) thin films (where x = 0, 5, 10, 15 and 20) of thickness 2000 Angstrom in the wavelength range 45 0-1000 nm. It is found that the optical bandgap decreases with the increase of Se98Bi2 concentration in the a-(Se(70)ioTe(30)) (100-x) (Se98Bi2)(x) sy stem. The value of refractive index (n) decreases, while the extinction coe fficient (k) increases with increasing photon energy. The results are inter preted in terms of concentration of localized states varying effective Ferm i level. (C) 2000 Elsevier Science B.V.. All rights reserved.