Structure and Crystallization Kinetics of As-Deposited Films of the GeTe Phase Change Compound from Atomistic Simulations

Models of the amorphous phase of the GeTe compound have been generated by depositing individual atoms on a substrate by molecular dynamics simulations. This material is of interest for applications in phase change memories. The kinetic energy of the atoms impinging on the surface is in the range 1.5-10 eV which is typical of magnetron sputtering growth. The simulations with up to 8000 atoms exploit a machine learning potential devised previously by the group. The structural properties of the films depend very little on the energy of the impinging atoms in the range 1.5-10 eV and they are also very similar to those of amorphous models generated by quenching from the melt, but for a larger fraction of Ge-Ge bonds and Ge atoms in tetrahedral geometries in the films. The crystal nucleation and growth are then simulated at 600 K which is close to the temperature of maximal crystal growth velocity exploited in the memory devices. Despite the structural differences mentioned above, the kinetics of crystallization at 600 K is very similar for the as-deposited and melt-quenched amorphous models.