Physical, optical and dielectric properties of Se85Te10X5 (X = Sn, In) films

Amorphous films of Se85Te10In5 and Se85Te10Sn5 were obtained from bulk compositions by thermal evaporation technique. The transmission T(lambda) of the examined films is measured as a function of wavelength (lambda)at a normal incident in range (500-2500 nm). Swanepoel's method was used to estimate the optical constants (the refractive index n and the absorption index k) for the considered films by using the T (lambda) values. The dispersion energy E-d, oscillator energy E-0, the lattice dielectric constant epsilon(infinity L) and high -frequency dielectric constant epsilon(s). values were determined. The type of optical band gap was indirect allowed transitions for the tested films. The Urbach's tail energy E-e was also computed. The effect of third element addition (Sn or In) to Se85Te15 on the optical parameters was examined. A connection between the coordination number < N-c <, the lone-pair electrons (L) and valence electrons (V) are calculated and a relation between them and the optical parameters was made.