Formation of Ge35In8S57 amorphous films for optical applications

Thin films of In-doped Ge-S in the form of Ge35In8S57 with different film thickness were deposited using an evaporation method. The X-ray diffraction studies demonstrate that the as-prepared films are amorphous in nature for these films. Some optical constants were calculated at a thickness of 150, 300, 450 and 900 nm and annealing temperature of 373, 413, 437 and 513 K. Our optical observations show that the mechanism of the optical transition obeys the indirect transition. It was found that the energy gap, Eg, decreases from 2.44 to 2.20 eV with expanding the thickness of the film from 150 to 900 nm. On the other hand, it was found that Eg increases with annealing temperature from 373 to 513 K. The increment in the band gap can be attributed to the gradual annealing out of the unsaturated bonds delivering a decreasing the density of localized states in the band structure. Using the single oscillator model, the dispersion of the refractive index is described. The dispersion constants of these films were calculated with different both thickness and annealing temperatures. Additionally, both of nonlinear susceptibility, χ(3) and nonlinear refractive index, n2 were calculated.