DETERMINATION OF THE OPTICAL GAP OF AMORPHOUS MATERIALS

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 (hwBAR) to the absorption coefficient alpha(w) i.e. [alphahwBAR approximately (hwBAR, -E(opt))r]. The present technique proposes the use of the inverse of the logarithmic derivative of optical data. A linear plot of the power law (alphahwBAR)1/r or (nalphahwBAR)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.