Absence of partial amorphization in GeSbTe chalcogenide superlattices

Phase-change materials (PCMs) are widely used for optical data storage due to their fast and reversible transitions between a crystalline and an amorphous phase that exhibit reflectivity contrast. In the last decade, PCMs have been found to be promising candidates for the development of nonvolatile electronic memories, as well. In this context, superlattices of thin layers of GeTe and Sb${}_2$Te${}_3$ show an unprecedented performance gain in terms of switching speed and power consumption with respect to bulk GeSbTe compounds. Models of crystalline-crystalline transitions, proposed to explain the improved properties, however, are challenged by recent experiments in which GeTe-Sb${}_2$Te${}_3$ superlattices are observed to reconfigure toward a van der Waals heterostructure of rhombohedral GeSbTe and Sb${}_2$Te${}_3$. Herein, ab initio molecular dynamics simulations are used to explore an alternative switching mechanism that comprises amorphous-crystalline transitions of ultrathin GeSbTe layers between crystalline Sb${}_2$Te${}_3$. Despite some positive results obtained by tailoring the quenching protocol, overall the extensive simulations do not yield clear evidence for this mechanism. Therefore, they suggest that the switching process probably involves a transition between two crystalline states. (© 2020 The Authors. Published by Wiley‐VCH GmbH)