First-principles study of adsorption and diffusion on Ge/Si(001)-(2 x 8) and Ge/Si(105)-(1 x 2) surfaces

Using first-principles total-energy Calculations, we have investigated the adsorption and diffusion of Si and Ge adatorns oil Ge/Si(0 0 1)-(2 x 8) and Ge/Si(1 0 5)-(1 x 2) surfaces. The dirner vacancy lines oil Ge/Si(0 0 1)-(2 x 8) and the alternate SA and rebonded SB steps on Ge/Si(1 0 5)-(1 x 2) are found to strongly influence the adatom kinetics. On Ge/Si(0 0 1)-(2 x 8) surface, the fast diffusion path is found to be along the dimer vacancy line (DVL), reversing the diffusion anisotropy on Si(0 0 1). Also, there exists a repulsion between the adatom and the DVL, which is expected to increase the adatom density and hence island nucleation rate in between the DVLs. Oil Ge/Si(1 0 5)-(1 x 2) surface, the overall diffusion barrier of Si(Ge) along (5 0 1) direction is relative fast with a barrier of similar to 0.83(0.61) eV, despite of the large surface undulation. This indicates that the adatorns can rapidly diffuse up and down the (1 0 5)-faceted Ge hut island. The diffusion is also almost isotropic along [0 1 0] and [3 0 1] directions. (C) 2007 Elsevier B.V. All rights reserved.