Zn- and Cd-induced features at the GaAs(110) and InP(110) surfaces studiedby low-temperature scanning tunneling microscopy - art. no. 125336

We used a low-temperature scanning tunneling microscope to study Zn- and Cd -doping atoms near the (110)-cleavage surfaces of GaAs and InP at 4.2 K. Th e filled-state images showed centro-symmetric elevations while the empty-st ate images showed circular depressions. We attribute these features to the influence of the Coulomb potential of the ionized doping atoms on the numbe r of states available for tunneling. In a few empty-state images of the GaA s(110) surface, the depressions were surrounded by maxima, which are probab ly direct observations of Friedel oscillations. For the InP(110) surface, a ll depressions were surrounded by noncentrosymmetric maxima. Upon moving th e tip Fermi level to the bottom of the conduction band, we observed that th e depressions turned into elevations with a triangular shape for both the G aAs(110) and the InP(110) surface. This shape was independent of the depth of the dopants, and the chemical nature of the dopants (Zn or Cd) did not i nfluence the triangular shape either. The orientation of these triangular f eatures was the same for all observed doping atoms and was geometrically de termined with respect to the host lattice. Furthermore, we determined the l ocation of a triangular feature with respect to a doping atom. The features were only visible when tunneling to the impurity band suggesting that the features are a direct image of the acceptor state although the origin of th e triangular shape is not clear at present.