Instability in Low-Temperature Molecular-Beam Epitaxy Growth of Si/Si(111)

Using high-resolution low-energy electron diffraction we studied in situ low-temperature molecular-beam epitaxial growth of Si/Si(111). At ~275 ^∘C and a deposition rate of ~7 bilayers/min, a roughening evolution occurs after an initial transient layer-by-layer growth. It shows dynamic scaling characteristics with a roughness exponent α≈1 and an interface growth exponent β=1/4. More importantly, the average local slope is found to increase with time as ~√ln(t). However, such a roughening behavior does not exist either at temperatures higher than 350 ^∘{}C or under a slower deposition rate of ~1 bilayer/min. The phenomena are consistent with a statistical model of linear diffusion dynamics.