Surface-defect formation on heavily doped InAs and GaAs layers studied by scanning tunneling microscopy

The surface atomic structure of GaAs and InAs layers heavily doped with Si is studied by using scanning tunneling microscopy. For GaAs, the straightness of dimer-vacancy rows is degraded by doping. The density df kinks in the rows coincides with the surface state density needed to move the surface Fermi level to the midgap. On the other hand, with InAs, the kink density is much lower than the surface-state density needed to move the level to the midgap. Self-consistent calculations of charge distribution in the neighborhood of the surface suggest that kink formation is governed by the competition between two processes: energy loss by new kink formation and energy gain by the electron trap from the conduction band to the surface state formed by the newly created kink Using this model, the low kink density observed for the InAs surface can be explained in terms of its small band gap of 0.36 eV.