The homoepitaxial assembly of a (001) GaAs surface from atomic gallium and molecular As_2 vapor fluxes has been investigated with molecular dynamics simulations using a recently developed bond-order potential. The approach enables dynamic atomic assembly events to be observed as atoms condense to form thin film structures. During simulation of epitaxial growth, we observed a temperature-dependent arsenic solubility limit consistent with experimental results. The As_2 sticking probabilities and dynamic dimer-surface binding states for both gallium- and arsenic-terminated (001) surfaces were also explored. On gallium-terminated surfaces, significant switching between two weakly bound precursor states and an intermediate chemisorbed state was observed during the surface diffusion of arsenic dimers. The switching frequency was strongly temperature dependent. The arsenic dimers bound to arsenic-terminated surfaces were found to be more likely to desorb (instead of diffuse) when thermally perturbed from their adsorption sites. This sticking probability was strongly dependent on surface temperature, atomic adsorption site environment, and the orientation of the incoming dimer.
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