Optical transmission data were obtained, for epitaxial thin films of the semiconducting silicide, which had been grown by pulsed laser deposition. An analysis of the defect densities showed that the values of the optical band-gap energy were effective band-gaps which had been decreased from their intrinsic values by the existence of band-tails in the density of states. It was suggested that this might account for the wide range of optical band-gap energies which had been reported for this material. It was also found that the energy width of the defect bands could affect the determination of the nature of the band-gap transition.

C.H.Olk, S.M.Yalisove, G.L.Doll: Physical Review B, 1995, 52[3], 1692-7