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 s how surfactant behaviour for epitaxial growth of Ge, important for dev ice applications. In this work we describe results of ab initio densit y functional calculations on the Si(001)(2 X 1)-Sb surface. The surfac e reconstruction is due to dimerisation of the Sb atoms in the directi on perpendicular to the dimer rows of the clean Si(001) surface. Our r elaxed 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 struc ture 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.