Symmetric Sb dimers and the possibility of mixed Si-Ge layers in the Sb/Ge/Si(100) surface

We present results of first-principles total-energy calculations of the Sb/Ge/Si(100) surface. The Sb top-layer atoms form symmetric dimers. Second-layer Ge atoms are also in symmetric positions. The calculated structure is similar to the Si(100)-(2 x 1)-Sb and Ge(100)-(2 x 1)-Sb surfaces. We have also investigated the possibility of Ge diffusion by fully relaxing the atomic positions of various Si(100) surfaces covered with one layer of Sb and one of Ge in different configurations. The total energy of one structure, with mixed Si-Ge second and third layers, is equal to the total energy of the nondiffusive case.