Importance of adsorbate-adsorbate interactions for As and Sb chemisorption on Si(100)

The chemisorption of As and Sb on both the Si(100)(1×1) ideal surface and the (2×1)-reconstructed surface is studied using the first-principles DMol method and cluster models (with up to 63 atoms), and the result shows that single As and Sb atoms adsorbed on the Si(100) ideal surface are predicted to have different stable adsorption sites, which implies that As and Sb will display different behavior on the Si surface. In fact, experiments show similar results for As and Sb for the adsorption site on the Si surface. A consistent result within the theoretical model and with the experimental results is achieved by including the metal-metal interaction at the surface. The metal-metal interaction is strongest when atoms are adsorbed at the modified bridge sites and oriented perpendicular to the underlying Si dimer rows. This leads to the formation of dimers on both the (2×1) and (1×1) surfaces. The optimized chemisorption geometries are determined by including substrate relaxation. The calculated structural parameters are in very good agreement with experiment and a previous pseudopotential calculation.