Mechanisms of Atomic Motion Through Crystalline GeTe

Abstract

Germanium telluride (GeTe) is an iconic functional material, both in itself and as the parent compound for a range of ternary phase-change data-storage alloys. Long taken to be a “simple” AB compound, crystalline GeTe is today known to contain a large number of germanium vacancies which directly affect the material’s macroscopic properties. Here, we use atomistic simulations to elucidate local mechanisms behind the motion of Ge atoms (and thus, vacancy diffusion) in crystalline GeTe. Transition pathways are computed using the nudged elastic band (NEB) approach at the gradient-corrected level of density-functional theory (GGA-DFT), both for the idealized rhombohedral (R3m) crystal and a number of defective configurations. Besides obvious structural arguments (i.e., beyond a simple rigid-sphere model), the diffusion barriers show a delicate dependence on the material’s electronic structure. The latter is controlled by vacancy formation, Sb adatoms, and charge injection, all of which is discussed in a unifie...