  A one-dimensional continuum description of growth on vicinal surfaces in the
presence of immobile impurities predicts that the impurities can induce step
bunching when they suppress the diffusion of adatoms on the surface. In the
present communication we verify this prediction by kinetic Monte-Carlo
simulations of a two-dimensional solid-on-solid model. We identify the
conditions where quasi one-dimensional step flow is stable against island
formation or step meandering, and analyse in detail the statistics of the
impurity concentration profile. The sign and strength of the impurity-induced
step interactions is determined by monitoring the motion of pairs of steps.
Assemblies containing up to 20 steps turn out to be unstable towards the
emission of single steps. This behavior is traced back to the small value of
the effective, impurity-induced attachment asymmetry for adatoms. An analytic
estimate for the critical number of steps needed to stabilize a bunch is
derived and confirmed by simulations of a one-dimensional model.

Statistical Mechanics;Materials Science