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We present a stochastic simulator for polycrystalline phase-change materialscapable of spatio-temporal modelling of complex anneals. This is based onconsideration of bulk and surface energies to generate rates of growth anddecay of crystallites built up of `monomers' that themselves may be quitecomplex molecules. We perform a number of simulations of this model using aGillespie algorithm. The simulations are performed at molecular scale and usingan approximation of local free energy changes that depend only on immediateneighbours. The sites are on a lattice that neither correspond to the crystallattice nor to individual monomers, but instead gives information about atwo-state local phase $r$ (where $r=0$ corresponds to amorphous and 1corresponds to crystalline) and a continuous crystal orientation $\phi$ at eachsite.  As an example we use this to model crystallisation in chalcogenide GST($GeSbTe$) alloys used for example in phase-change memory devices, wherereversible changes between amorphous and crystalline regimes are used to storeand process information. We use our model to simulate anneals of GST includingones with non-trivial spatial and temporal variation of temperature; this givesgood agreement to experimental incubation times at low temperatures whilemodelling non-trivial crystal size distributions and melting dynamics at highertemperatures.

A fast simulator for polycrystalline processes with application to phase change alloys