Thermal transport in phase-change materials from atomistic simulations

We computed the thermal conductivity (κ) of amorphous GeTe by means of classical molecular dynamics and lattice dynamics simulations. GeTe is a phase change material of interest for applications in nonvolatile memories. An interatomic potential with close-to-ab initio accuracy was used as generated by fitting a huge ab initio database with a neural network method. It turns out that the majority of heat carriers are nonpropagating vibrations (diffusons), the small percentage of propagating modes giving a negligible contribution to the total value of κ. This result is in contrast with the properties of other amorphous semiconductors such as Si for which nonpropagating and propagating vibrations account for about one half of the value of κ each. This outcome suggests that the value of κ measured for the bulk amorphous phase can be used to model the thermal transport of GeTe and possibly of other materials in the same class also in nanoscaled memory devices. Actually, the contribution from propagating modes, which may endure ballistic transport at the scale of 10–20 nm, is negligible.