Strong intensity oscillations have been found in RHEED during epitaxial growth at 77 K. This temperature is too low for thermally activated diffusion and establishes that the deposited atom uses its latent heat of condensation to skip across the surface, preferentially coming to rest at growing island edges, to achieve quasi---layer-by-layer growth. This growth mechanism implies that RHEED oscillations should be observable at 0 K. The data also provide insight into the basic principles governing RHEED oscillations.