Ge(Si) ordering on a double-layer, stepped Si(Ge)(001) surface

Using the Car-Parrinello scheme, we study atomic ordering of Ge(Si) on a double-layer, stepped Si(Ge)(001) surface. We introduce a rebonded D _B step to find a stable absorption site of the Ge(Si) atoms. We find that the Si atoms on a Ge surface favor subsurface sites near the step edge. The total energy is lowered by the rebonded atom forming an asymmetry, which increases the dehybridization on the rebonded atom. This leads to a compositional ordering along the direction of the dimer row. We will also show that the simple Vegard law is not always obeyed at the interface, in particular, in the initial growth process.