Atomistic Simulations of the Crystallization Kinetics of Ge₂Sb₂Te₅ and GeTe in Confined Geometries

Phase change alloys are among the most promising materials for the realization of artificial neurons<br/>and synapses for neuromorphic computing. In these applications, one exploits the different resistive<br/>levels that can be realized by full or partial crystallization of the amorphous phase upon application<br/>of current pulses. In a recent work [1], it was proposed that a superlattice (SL) geometry made of<br/>alternating layers of the phase change material Sb₂Te₃ and more thermally stable confining layers of<br/>TiTe₂ woud exhibit superior properties for neuromorphic computing. However, Sb₂Te₃ suffers from<br/>insufficient data retention due to its low crystallization temperature T_x . Substituting Sb₂Te₃ with a<br/>phase change compound with a higher T_x, such as GeTe or Ge₂Sb₂Te₅ (GST), seems an interesting<br/>option in this respect. Nanoconfinement might, however, alters the crystallization kinetics with<br/>respect to the bulk. In this contribution, we will discuss the results of molecular dynamics<br/>simulations of the crystallization process of Ge₂Sb₂Te₅ and GeTe [2] nanoconfined in geometries<br/>mimicking GST/TiTe₂ or GeTe/TiTe₂ superlattices. To this aim, we performed large scale<br/>simulations with machine learning interatomic potentials [3,4]. The simulations reveal that<br/>nanoconfinement induces a mild reduction in the crystal growth velocities which would not hinder<br/>the application of GST/TiTe₂ or GeTe/TiTe₂ heterostructures in neuromorphic devices with superior<br/>data retention.<br/>[1] K. Ding et al, Science 366, 210 (2019)<br/>[2] D. Acharya, O. Abou El Kheir, D. Campi, and M. Bernasconi , Sci. Rep. 14, 3224 (2024)<br/>[3] O. Abou El Kheir, L. Bonati, M. Parrinello, and M. Bernasconi, npj Comp. Mater. 10, 33 (2024)<br/>[4] S. Gabardi et al, J. Phys. Chem. C 121, 23827 (2017)