Composition dependence of structural and optical properties of GexSe100-x semiconducting thin films

The studied thin films of GexSe100-x compositions were synthesized with thermal evaporation technique at room temperature. The effect of composition on the structure of the prepared films was characterized by X-ray diffraction and scanning electron microscopy. The stoichiometry of the studied compositions was examined by energy dispersive X-ray spectroscopy. The film thickness and refractive index were calculated by Swanepoel's method. The structural analysis showed that the as-prepared GexSe100-x (x = 10, 15, 20 and 30 at.%) films exhibit the amorphous state while other films containing 25, 35 and 40 at.% of Ge are polycrystalline. On the other hand, the GeSe and Se crystalline phases are obtained for the annealed films. The analysis of the optical spectra showed that Eg increases with increasing Ge content up to a x = 30 at.% and then decreases with further increase of the Ge concentration. Other many optical parameters such as optical conductivity, dispersion energy and dissipation factor were determined and strongly affected by the variation of the composition.