Investigation of structural and optical properties of amorphous-crystalline phase transition of As40S45Se15 thin films

Abstract

In the present work, the influence of heat treatment on the structural and optical properties of amorphous As40S45Se15 chalcogenide thin films is investigated. The structural analyses of the thin films have been studied via X-ray diffraction technique. The X-ray diffraction studies exhibit that the crystallinity improves with increase of the thermal annealing temperature from inset temperature to maximum crystallization temperature. On the other hand, the optical constants of the as-prepared and annealed As40S45Se15 samples were computed via envelope method. Then, the optical band gap of as-prepared and annealed samples as a function of photon energy in the wavelength range 400–2500 nm were investigated. The optical band gap was successfully calculated by Tauc’s relation which exhibits the indirect transitions for the as-prepared and annealed samples under onset temperature and allowed direct transition for annealed samples at and above inset temperature. The dispersion parameters of the films were computed via the single oscillator model proposed by the Wemple–DiDomenico relation. The static refractive indices (both linear and non-linear) optical susceptibility χ(1), χ(3), and then non-linear refractive indices were also computed. Starting with dielectric constants (εr and εi) the loss tangent and volume/surface energy loss functions were computed. Also the inter-band transition strength Jcv(E) for the dipole selection rules for the transitions was discussed.