Structural and optical properties of thermally evaporated and annealed Ge20Se76Sn4 thin films

Amorphous Ge20Se76Sn4 thin films of thickness similar to 150 nm were prepared, from bulk Ge20Se76Sn4, by thermal evaporation technique. The differential scanning calorimetry analysis of bulk Ge20Se76Sn4 exhibits one glass transition, one crystallization peak, and one melting point. The inclusion of Sn by substituting Se or Ge-atoms into the Ge-Se matrix has been studied using energy-dispersive spectral X-ray, and Fourier-transform infrared spectroscopy. The X-ray diffraction affirms that films annealed at annealing temperature (Ta) <= 553 K are amorphous; meanwhile, films annealed at Ta >= 603 K are crystalline. It was found that the annealing process can be used to tune the linear and nonlinear optical parameters and constants. The decrease in the indirect optical bandgap energy (E-g) with an increase in Ta for Ta >= 603 K could be ascribed to the increase in the crystallinity and increasing the density of defects in the bandgap. The estimated E-g were correlated with the refractive index (n) using seven different approaches and the average value of n was increased as Ta increased. It is suggested that the structural, and optical characteristics of the thermally evaporated Ge20Se76Sn4 thin films can be tuned and engineered by the annealing process. Profound analysis of optical parameters for the Ge20Se76Sn4 thin films suggests the utilization of these glasses for numerous photonic applications.