  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.
