Atomistic Simulations of the Crystallization and Aging of GeTe Nanowires

Nanowires
made of chalcogenide alloys are of interest for use in
phase-change nonvolatile memories. For this application, insights
into the thermal properties of such nanowires and, in particular,
into the crystallization kinetics at the atomic level are crucial.
Toward this end, we have performed large-scale atomistic simulations
of ultrathin nanowires (9 nm in diameter) of the prototypical phase-change
compound GeTe. We made use of an interatomic potential generated by
the neural network fitting of a large ab initio database to compute
the thermal properties of the nanowires. By melting a portion of a
nanowire, we investigated the velocity of recrystallization as a function
of temperature. The simulations show that the melting temperature
of the nanowire is about 100 K below the melting temperature of the
bulk, which yields a reduction by about a factor of 2 of the maximum
crystallization speed. Further, analysis of the structural properties
of the amorphous phase of the nanowire suggests a possible origin
of the reduction of the resistance drift observed experimentally in
nanowires with respect to the bulk.