Study of the absorption properties of amorphous solids

Using the effective mass approach, Tauc's relation for the absorption coefficient is reinvestigated. Two different forms for the dependence of the absorption coefficient on the photon energy <$>hbar<$> are derived. The proportionality constants in both the relations are calculated theoretically using the appropriate effective masses, and compared with their experimental estimates. It is suggested that deviations from Tauc's relation may be attributed to the energy dependent transition matrix element. Merits and demerits of both forms are discussed in view of the experimental data available.