Roughening due to edge diffusion for irreversible aggregation

We show that fast edge diffusion in a simple kinetic Monte Carlo simulation for epitaxial growth enhances surface roughening for a model of irreversible aggregation. The reason for this is a simple, but rather subtle effect: Faster edge diffusion makes the islands more compact, leading to a significant adatom concentration on top of islands at earlier times. As a consequence, nucleation in higher layers occurs faster, increasing the surface roughness. We also demonstrate that fast edge diffusion can effectively contribute to diffusion of small clusters, and can produce unexpected scaling results.