Structure and photoinduced changes in As-S-Te bulk glasses and amorphous layers

Bulk glasses and thin layers from the system (As0.33S0.67)(100-x)Te-x, where x = 0, 1, 5, 10, were prepared, and the photoinduced changes that they exhibit were studied. From the spectral dependence of the refractive index, the dielectric constant, epsilon(infinity), the single oscillator energy, E-o, and the dispersion energy, E-d were calculated using the Wemple-DiDomenico equation. The changes that occur in these quantities as a result of the addition of Te to the glass, or of illumination, are explained on the basis of the different polarization of As and S atoms in comparison with the larger Te atoms, together with changes in coordination and photoinduced changes in the optical gap E-g(opt). The redistribution of chemical bonds that arises from Te addition and/or illumination has been determined using IR and Raman spectroscopy. Addition of Te and/or exposure causes increased ordering of the structure as a result of the increase in heteropolar bonds concentration. (C) 1998 Elsevier Science S.A.