Ab initio computer simulations of non-equilibrium radiation-induced cascades in amorphous Ge₂Sb₂Te₅

Ion irradiation corresponds to a process that involves the production of non-equilibrium cascades in the host material, and the atomistic modelling of such events in glasses is challenging. Here, non-equilibrium cascades in amorphous Ge₂Sb₂Te₅ phase-change memory material have been investigated by means of first-principles molecular-dynamics simulations. A stochastic boundary-conditions approach is employed to treat the thermal nature of the cascades and drive the modelled system back to equilibrium in a natural way, while four different initial thermal-spike energies are considered. A comprehensive analysis of the cascade evolution is presented with respect to the kinetic profile and the dynamics of the cascade inside the glass structure. The modelling results show that the instantaneous maximum kinetic energy decays rapidly with time, and that the time-scale of the ballistic phase of the cascade inside the glass model is very short. The quality of the implemented approach is validated through a comparison of the calculated structure factor for the modelled glasses with experimental data from the literature. Analysis of the bonding for all the species in the glass structure highlights particular structural modifications in the connectivity of the amorphous network due to the simulated cascade.