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 X 1) ideal surfac e and the (2 X 1)-reconstructed surface is studied using the first-pri nciples 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, whic h implies that As and Sb will display different behavior on the Si sur face. In fact, experiments show similar results for As and Sb for the adsorption site on the Si surface. A consistent result within the theo retical model and with the experimental results is achieved by includi ng the metal-metal interaction at the surface. The metal-metal interac tion is strongest when atoms are adsorbed at the modified bridge sites and oriented perpendicular to the underlying Si dimer rows. This lead s to the formation of dimers on both the (2 X 1) and (1 X 1) surfaces. The optimized chemisorption geometries are determined by including su bstrate relaxation. The calculated structural parameters are in very g ood agreement with experiment and a previous pseudopotential calculati on.