Towards controlled molecular beam epitaxial growth of artificially stacked Si: Study of boron adsorption and surface segregation on Si(111)

摘要

Creating rotation twins periodically in a defined distance within Si layers could lead to the formation of miscellaneous Si crystal structures. This could be realized by several growth and annealing cycles on heavily B-covered Si(111) exhibiting (√3×√3)R30° surface superstructure. However, surface defects due to imperfections of the B-induced surface structure give rise to an inhomogeneous Si nucleation, which limits the structure size. Therefore, surface structure formation induced by both adsorption and surface segregation of B on Si(111) and its influence on the Si molecular beam epitaxial growth mode has been investigated using ultraviolet photoelectron spectroscopy and accompanying reflection high-energy electron diffraction. Based on these studies, conditions have been established to prevent surface defects. Furthermore, annealing samples with 0.6 monolayers (ML) B buried below several ML Si at 1080 K results in a renewal of the B-induced Si surface structure without any defects. This indicates a dominance of B surface segregation over bulk diffusion, which becomes significant only above 1100 K.