Bonding and structure of the Si(001)(2x1)-Sb surface

A thin layer of Sb adsorbed on to the Si(001) surface is believed to show surfactant behaviour for epitaxial growth of Ge, important for device applications. In this work we describe results of ab initio density functional calculations on the Si(001)(2 X 1)-Sb surface. The surface reconstruction is due to dimerisation of the Sb atoms in the direction perpendicular to the dimer rows of the clean Si(001) surface. Our relaxed geometry is found to be in accord with recent theoretical work and SEXAFS measurement in predicting a structure with symmetric dimers. Furthermore, we investigate the nature of the bonding and band structure of the relaxed Sb-capped surface. We find that the normal energy ordering of ungerade and gerade pi orbitals localised on the Sb dimer is reversed.