Mixed Ge-Si dimer formation in Ge/Si(100) and Si/Ge(100) growth

We report on the energetics of the mixed Ge-Si dimer formation and adatom d iffusion into subsurface layers for various dimer structures on Si(100) and Ge(100) surfaces through first-principles total-energy calculations. On bo th Si and Ge(100) surfaces, the mixed dimer formation is found to be more f avorable than the pure Si-Si and Ge-Ge dimer formation. For Ge atoms on Si( 100), the diffusion into the subsurface layers is not energetically favorab le and thus, the mixed Ge-Si dimer is stable against the subsurface diffusi on. For Si atoms on Gc(100), the diffusion of Si into the subsurface layer, which segregates Ge atoms onto the surface, is found to be more favorable than remaining as part of mixed Ge-Si dimers.