First principles study on the geometry and stability of the Ge atom in initial Ge growth on the Si(001) surface

Based on generalized gradient approximation (GGA) density functional calculations, the optimized structures of the Si(001)-Ge surfaces, where Ge atoms partially replace Si atoms, are determined. The significant floating up of the Ge atom at the up-atom dimer site suggested by an X-ray photoelectron diffraction experiment at 0.1 ML is not reproduced. The relative concentration of the Ge in the third and the fourth layers to that in the first layer is found to be 10-15%, which is of the same order as suggested experimentally. The coverage dependence of the penetration is also evaluated. The possibility of a Ge-Si mixed dimer ca 0.1 ML is studied taking into account the stabilization of the initial and the final states forming dimers or dimer rows. (C) 1999 Elsevier Science B.V. All rights reserved.