The effect of impurities on epitaxial growth in the submonolayer regime is studied using kinetic Monte Carlo simulations of a two-species solid-on-solid growth model. Both species are mobile, and attractive interactions among adatoms and between adatoms and impurities are incorporated. Impurities can be codeposited with the growing material or predeposited prior to growth. The activated exchange of impurities and adatoms is identified as the key kinetic process in the formation of a growth morphology in which the impurities decorate the island edges. The dependence of the island density on flux and coverage is studied in detail. The impurities strongly increase the island density without appreciably changing its power-law dependence on flux, apart from a saturation of the flux dependence at high fluxes and low coverages. A simple analytic theory taking into account only the dependence of the adatom diffusion constant on impurity coverage is shown to provide semi-quantitative agreement with many features observed in the simulations.
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