GROWTH OF GERMANIUM FILMS ON SI(001) SUBSTRATES

We have studied the growth of Ge layers on the Si(001) surface using molecular-dynamics techniques. In order to relieve the strain resulting from the lattice mismatch between Ge and Si atoms, Ge deposited on the Si(001) surface tends to form islands. This tendency to form three-dimensional structures was studied by monitoring the chemical potential of relaxed Ge films on top of the Si(001) surface. We find that layer-by-layer growth is favored for the first three layers of Ge deposited. To study the diffusion of Ge adatoms on Ge(n)Si(001) films, we have mapped out the potential-energy surfaces on such films with (2 X 1) and (2 X N) reconstructions. For surfaces subject to (2 X 1) reconstructions, the motion is anisotropic, with the fast-diffusion direction being along the dimer rows. In the case of a surface with (2 X N) reconstructions, fast diffusion is still along the dimer rows. However, we find additional potential-energy barriers where the missing dimers are located, which effectively confines the motion of adatoms. Finally, we have studied the initial stages of island formation by directly simulating the epitaxial growth of Ge layers on the Si(001) surface.