DETERMINATION OF THE OPTICAL GAP OF AMORPHOUS MATERIALS

A computational method is applied for the analysis of optical absorpti on spectra of amorphous materials to obtain both the power index, r, a nd 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 powe r law (alphahwBAR)1/r or (nalphahwBAR)1/r where n is the refractive in dex of the material is obtained without needing an arbitrary assumptio n 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.