Improving carbon penetration in Si (0 0 1) surfaces by acting on the surface Si-defects

We present a theoretical study of the influence of silicon ad-dimers on carbon incorporation in the Si(0 0 1) surface. We consider configurations involving either ad-dimers located directly above the dimer rows of the defectless Si(0 0 1) surface, or ad-dimers located between the dimer rows. In both cases, the presence of ad-dimers makes carbon penetration in the subsurface layers easier. The energetic barrier at the crossing of the second layer substantially decreases or vanishes, and the third layer is always favoured. Carbon adsorption is more likely in α than in β type sites, but the difference can be less important in the presence of ad-dimers. The effects of carbon-defect interaction and local geometry (Si-C distances) are also investigated. Our results suggest that acting on the surface defects might improve carbon penetration in Si(0 0 1) and allow a better control of the carbon atoms positions in the subsurface layers.