Photostructural relaxation in As–Se–S glasses: Effect of network fragility

The effect of photoinduced structural relaxation in As–S–Se glass is investigated during sub-bandgap irradiation. It is shown that the glass undergoes rapid optically induced structural relaxation upon photoexcitation of bonding electrons. Fragile systems exhibit larger relaxation as expected from their enthalpy profile. This suggests that the process is thermodynamically driven and that the kinetic impediment to relaxation at low temperature is lifted through photoinduced softening of the glass matrix. Activation energy for enthalpy relaxation measurement and an annealing study near T_g show that the photorelaxation effect is not a thermally activated process. The 〈r〉 dependence of photostructural changes is addressed and explained using the energy landscape formalism.