Simulation of the structure of GeAs4Te7 chalcogenide materials during memory switching

Abstract

The complex chalcogenides with excellent memory switching properties are mainly situated close to the border of glass formation domain. The simulation of the structural changes occurring during the memory switching process of a ternary chalcogenide composition has been carried out. The transition of a high resistivity GeAs4Te7 amorphous cluster with 120 atoms to a low resistivity crystalline cluster was analyzed. The coordination of atoms changes from that corresponding to 8-N coordination rule (two for tellurium, three for arsenic, and four for germanium) in the amorphous phase to six (the same for all atoms) in metastable crystalline phase. Because of spatial constraints exercised by the amorphous matrix, the amorphous cluster cannot expand. In these circumstances Te atoms seem to be over-coordinated (up to sixfold-coordinated). During the switching process, the atoms are moving on distances up to 4.0 Å. The average displacement is of 2.36 Å.