Thermal-induced gradually changes in the optical properties of amorphous GeSe2 film prepared by PLD

Amorphous GeSe2 film was prepared by the pulsed laser deposition technique and annealed at different temperature from 473 to 623 K. Using the ‘non-direct transition’ model proposed by Tauc, the short wavelength absorption edges of the films were well fitted and the optical band gaps (Egopt) were determined. The Tauc slope of the as-deposited film is smaller than those of annealed films, which were proposed as an indicator of the degree of structural randomness of amorphous semiconductors. The refractive index and thickness of the films were calculated from the optical transmission spectra using the Swanepoel method. The index of refraction decreased while Egopt increased gradually with increasing the annealing temperature. The thermal-bleaching and thermal-contraction effects were observed, which were interpreted as the reduction in the density of homopolar bonds according to the Raman spectra analysis and the diminution of porous structure in the fragments of the annealed films, respectively.