Adsorption of group III atoms on SiC(111) surfaces

We investigate the adsorption of boron and aluminium on beta-SiC(111)root 3 x root 3R30 degrees surfaces by means of first-principles structure calcul ations utilizing density functional theory in its local density approximati on. We focus on potential surfactant effects of group III adsorbates concer ning 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 T-4 site, whereas boron occupies the so-called S-5 site substituting a carbon atom. However, in contrast to the adsorption on Si(111) we find a se cond 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 ad sorbate models. (C) 2000 Elsevier Science B.V. All rights reserved.