Structural stability and adatom diffusion at steps on hydrogenated Si(100) surfaces

We present first-principles total-energy calculations which reveal microscopic structures of the steps and mechanisms of the adatom diffusion on hydrogenated Si(100) surfaces. Energetics among several types of the steps depends on the hydrogen chemical potential mu(H), and the nonrebonded structure is more stable than the rebonded one fur a wide range of mu(H). Calculations of the diffusion pathways and activation barriers for the adatom show that the Schwoebel barrier is absent near the single-layer steps. It is also found that the nonrebonded S-B step is a deep sink for the adatom in epitaxial growth.