The surface atomic structures of layers that were heavily doped with Si were studied by means of scanning tunnelling microscopy. In the case of GaAs, the straightness of the dimer-vacancy rows was degraded by doping. The density of kinks in the rows agreed with the surface state density that was required to move the surface Fermi level to the mid-gap. In the case of InAs, the kink density was much lower than the surface-state density that was required to move the level to the mid-gap. Self-consistent calculations of the charge distribution in the neighborhood of the surface suggested that kink formation was governed by the competition of 2 processes. These were energy loss due to new-kink formation, and energy gain by electron trapping from the conduction band to the surface state that was formed by the newly created kink. By using this model, the low kink density that was observed at the InAs surface could be explained in terms of its narrow band-gap of 0.36eV.

H.Yamaguchi, Y.Horikoshi: Physical Review B, 1996, 53[8], 4565-9