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 irreversib le aggregation. The reason for this is a simple, but rather subtle effect: Faster edge diffusion makes the islands more compact, leading to a signific ant adatom concentration on top of islands at earlier times. As a consequen ce, nucleation in higher layers occurs faster, increasing the surface rough ness. We also demonstrate that fast edge diffusion can effectively contribu te to diffusion of small clusters, and can produce unexpected scaling resul ts.