Physical aging effects on the structural and optical properties of nano As-Se-Tl films

Abstract As20Se65Tl15 films of thickness of 400 nm as a candidate of As-Se-Tl films were prepared by thermal evaporation technique under a vacuum of 10− 6 Torr. The aging of these films for 4 and 8 months and were studied. The as deposited films have amorphous nature and the aged films have (170) and (432) preferred nanocrystalline orientations. The crystallite size of 8 months aged films are 22 and 43 nm respectively. Within the wavelength range (200 − 1100) nm, optical parameters were measured and the optical constants were calculated within the visible range. Indirect electronic transition was dominated. The value of the optical energy gap, Egiopt increases with aging from 1.68 to 1.82 eV. The dispersion parameters were studied by single oscillator model. Aging process increases the values of N/m⁎ and Eo while decreases the values of n, e∞, eL and Ed. The obtained changes were attributed to structural enhancement and ordering due to aging process. The single oscillator model is used to describe spectrum of refractive index. Free carriers concentration makes a difference between e∞ and eL values. The calculated values of e1 are higher than the values of e2. The Optical conductivity as well as VELF and SELF were also studied.