Effect of composition on refractive index dispersion in Ge-Sb-S thin films

Ge/sub x/Sb/sub 40-x/S/sub 60/ thin films are studied by means of spectrophotometry in the light wavelength region of 0.5-2.5 /spl mu/m. The refractive index value were determined from the transmission spectra. The dispersion parameters E/sub 0/ and E/sub d/ were evaluated and considered in term of the average coordination number Z. The compositional dependences exhibit a peculiarity around Z=2.65-2.67 which can be connected with a topological phase transition of the film structure.