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 has been investigated by means of scanning tunneling microscopy at room temperature for samples with dopant concentrations below and above the metal-insulator transition. Domains and extended anti-phase boundaries are observed due to the formation of the 2 x 1 reconstruction. During the scanning process the location of these anti-phase boundaries can change reversibly, suggesting a tip-induced modification of the boundaries. On an atomic scale, individual P atoms in the Si host lattice can be identified because of their voltage-dependent image contrast caused by the Coulomb potential of the ionized donor. This permits an analysis of the spatial arrangement of the donors, which obeys a statistical distribution with a low-distance cut-off, in agreement with the minimum nearest-neighbor distance estimated from the solubility Limit. Significant clustering can be ruled out even for concentrations far above the metal-insulator transition.