Comparative study of Sb bonding on group-IV semiconductor (001) substrates

We present the results of ab initio pseudopotential density-functional calculations for the geometry and bonding of the Si(001)/Sb(2 x 1) and Ge(001)/Sb(2 x 1) surfaces. The Sb dimers are found to be symmetric, with bond lengths of 2.96 and 2.92 Angstrom on the Si and Ge substrates, respectively. We thus concur with recent theoretical work, which concluded that the asymmetric Sb dimer model for the Ge substrate, favored by surface x-ray-diffraction studies, is incorrect. Furthermore, we calculate that the monolayer-averaged chemisorption energy of Sb on the Si substrate is 0.48 eV per dimer greater in magnitude than on the Ge substrate, and discuss the implications for surfactant-mediated growth.