Study the atomic mechanism in epitaxial growth on semiconductors

For the first time, the concept of reaction-limited aggregation (RLA) in epitaxial growth is proposed. The first RLA system, Ge heteroepitaxy on Si(111) mediated by one monolayer of Pb, has been identified with a UHV-STM. The nucleation and growth behaviors of the RLA system are very different from traditional concepts of epitaxial growth. In many aspects, the behaviors are even opposite to predictions based on traditional nucleation theories, which assume negligible energy barriers for the nucleation and growth processes. We found that traditional theories were in the diffusion-limited regime. Our RLA system exhibits behaviors in the opposite regime, which clearly indicate the limitation of traditional nucleation theories and may have important implication for development of a more comprehensive nucleation theory in the future. Besides the RLA concept, the results also suggest that clusters may play a more important role than single atoms in the nucleation and growth processes. (Physical Review Letters 80, 4229 (1998); Physical Review Letters 83, 1191 (1999); Physical Review Letters 97, 089601 (2006))