Influence of boron on the initial stages of Si molecular beam epitaxy on Si(1 1 1) studied by reflection high-energy electron diffraction

The influence of boron as a function of coverage on molecular beam epitaxial Si growth on Si(1 1 1) surface was systematically studied by reflection high-energy electron diffraction. At boron coverage above 0.3 monolayer regular oscillations occur with a period typically for two-bilayers, whereas at lower boron coverage a transient behaviour with irregular intensity oscillations was observed in the initial growth stages. This behaviour can be attributed to a superposition of a bilayer and a two-bilayer dominated growth mode. The appearance of these two growth modes is discussed in terms of an initial surface defect-induced nucleation of bilayer-high Si islands and the formation of two-bilayers-high Si islands on top of the van der Waals like boron-covered surface, respectively. We suggest that these surface defects are of intrinsic nature, and their number only depends on the amount of boron at the surface. The oscillations become regular during further Si deposition with a bilayer period, indicating a diminishing influence of the layer/substrate interface on the growth processes.