SCANNING TUNNELING SPECTROSCOPY OF CHARGE EFFECTS ON SEMICONDUCTOR SURFACES AND ATOMIC CLUSTERS

We have used scanning tunneling microscopy and scanning tunneling spec troscopy at liquid helium temperature to study the electronic structur e of in situ cleaved, (110) oriented surfaces of InAs single crystals. Both unperturbed, atomically flat areas and areas with an atomic-size defect cluster have been investigated. We show that the anomalous beh avior of the local tunneling conductivity, which indicates a pronounce d enhancement of the semiconductor band gap for the flat areas, is con sistent with band bending induced by charges localized at the apex of the tip. Atomic-size defect clusters contain additional charges which modify the band bending; this explains the different behavior of the t unneling conductivity near the defect cluster. The experimentally obse rved oscillations of the tunneling conductivity near the band gap edge s can be directly related to resonant tunneling through quantized surf ace states which appear because of the band bending. (C) 1998 American Institute of Physics.