Energetics of substitutional carbon in hydrogenated Si(100)

We present first-principle total-energy calculations of carbon incorporation in the hydrogen-saturated (formula presented) surface. A large variety of atomic configurations involving one, two, and four substitional C impurities in surface and subsurface sites is considered. While carbon incorporation in the surface layer is energetically favored, C-C interactions play an important role and can stabilize configurations that would be otherwise unlikely, particularly configurations with carbon atoms in the 5th layer, as observed in recent x-ray photoelectron-spectroscopy experiments.