Determination of the optical gap of amorphous materials

Abstract

A computational method is applied for the analysis of optical absorption spectra of amorphous materials to obtain both the power index, r, and E opt, the optical band gap, from the theories of Tauc, and Davis and Mott which relate the energy of the incident photon (hw) to the absorption coefficient α(w) i.e. [αhw ∼ (hw-E opt)'] The present technique proposes the use of the inverse of the logarithmic derivative of optical data. A linear plot of the power law (αhw)1/r or (nαhw)1/r where n is the refractive index of the material is obtained without needing an arbitrary assumption about the exponent involved. Experimental data on SiO, SiO/B2O3 and SiO/As2O5 amorphous thin films have been re-analysed and much accurate values of r and E opt are reported.