Group-III Adatoms on Silicon Surfaces

Abstract

On Si(111) surfaces, group-III atoms induce $(\sqrt 3 \times \sqrt 3 )R30^\circ$R30° reconstructions. Al, Ga, and In atoms have larger covalent radii than silicon and adsorb in T4 sites. Each of the trivalent adatoms thus saturates the dangling bonds of three silicon surface atoms. Boron, on the other hand, has a much smaller covalent radius than silicon and, therefore, bonds between boron atoms occupying T4 sites and nearest-neighbor silicon atoms would be strongly elongated. Substitutional S5 sites beneath silicon atoms in T4 sites are energetically much more favorable configurations for the small boron atoms.