Investigation of the (111) surface of P-doped Si by scanning tunneling microscopy

The (111) surface of P-doped Si obtained by cleaving in ultrahigh vacuum ha s been investigated by means of scanning tunneling microscopy at room tempe rature for samples with dopant concentrations below and above the metal-ins ulator transition. Domains and extended anti-phase boundaries are observed due to the formation of the 2 x 1 reconstruction. During the scanning proce ss the location of these anti-phase boundaries can change reversibly, sugge sting a tip-induced modification of the boundaries. On an atomic scale, ind ividual P atoms in the Si host lattice can be identified because of their v oltage-dependent image contrast caused by the Coulomb potential of the ioni zed donor. This permits an analysis of the spatial arrangement of the donor s, which obeys a statistical distribution with a low-distance cut-off, in a greement with the minimum nearest-neighbor distance estimated from the solu bility Limit. Significant clustering can be ruled out even for concentratio ns far above the metal-insulator transition.