OPTICAL-PROPERTIES OF THIN GEXSE1-X AMORPHOUS FILMS

The optical constants of Ge(x)Se1-x amorphous thin films of different thicknesses (23-335 nm) and of different compositions (0.05 less-than-or-equal-to x less-than-or-equal-to 0.30) were determined in the wavelength range 400-2000 nm. It was found that both the refractive index n and the absorption index k are independent of the film thickness for a given solution, whilst there is a distinct dependence of n and k on the Ge content. The linearity of alpha-1/2 = f(hv) yields the existence of indirect optical transitions. The corresponding forbidden band gaps were determined. The variation of the energy gap with x for Ge(x)Se1-x amorphous thin films was found to obey the relation E(GeSe) = YE(Ge) + (1-Y)E(Se), where Y is the volume fraction of Ge.