Group-III Adatoms on Silicon Surfaces

Abstract

On Si(111) surfaces, group-III atoms induce (√3 × √3)R30^o reconstructions. Al, Ga, and In atoms have larger covalent radii than silicon and adsorb in T ₄ 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 T ₄ sites and nearest-neighbor silicon atoms would be strongly elongated. Substitutional 65 sites beneath silicon atoms in T ₄ sites are energetically much more favorable configurations for the small boron atoms.