Amorphous Ge_xSe_1-x and its hierarchical structures by mean of molecular dynamics simulations

Amorphous chalcogenides, such as Ge_xSe_1-x, have been proposed as good candidates as ovonic switch materials for nonvolatile memories and selectors applications due to their fast switching, endurance and higher crystallization temperature respect to standard GST compounds. The electrical properties of Ge_xSe_1-x, as for other chalcogenides, are related to the presence of short- and medium-range structures in the amorphous state. To describe the structure of Ge_xSe_1-x in the 0.4-0.6 range at the atomic level, we employed classical molecular dynamics (MD) simulations of large systems and for long timescales allowing the structural rearrangement of the amorphous state at room temperature.
We found that MD simulations well reproduce all the main features of both the short- and medium-range order structures. Amorphous Ge_xSe_1-x shows different level of ordering depending on the relative Ge content. Se-rich compounds are characterized by a high interconnected network with a high percentage of rings. Moreover, we demonstrated that the amorphous structure description requires simulating the systems for timescales in the order of tenth of nanoseconds, that are inaccessible through ab initio techniques.