Adsorption of group III atoms on SiC(111) surfaces

We investigate the adsorption of boron and aluminium on β-SiC(111)3×3R30° surfaces by means of first-principles structure calculations utilizing density functional theory in its local density approximation. We focus on potential surfactant effects of group III adsorbates concerning epitaxial growth of SiC. For both adatoms considered we find the same sites as favoured for adsorption on Si(111) surfaces: aluminium adsorbs on the T4 site, whereas boron occupies the so-called S5 site substituting a carbon atom. However, in contrast to the adsorption on Si(111) we find a second interface phase for the boron adsorption under carbon-rich conditions energetically favourable where boron substitutes for an Si atom. We discuss geometrical, energetic and electronic properties of the most favourable adsorbate models.