Local Fermi-level pinning at a single adatom (Cs) or vacancy (As) on a GaAs(110) surface

Local surface photovoltage imaging with a scanning tunneling microscope is used to demonstrate two types of local Fermi-level pinning next to a single adsorbate or defect, taking advantage of the tip-induced band bending due to the lack of gap states at clean GaAs(110) surfaces. The pinning energy a t a single cesium adatom location was determined to be 0.56 +/- 0.04 eV abo ve the valence-band maximum (VBM), while for As vacancy, the Fermi level ca nnot go below the top of a filled surface state, 0.62 +/- 0.04 eV above the VBM. [S0163-1829(99)51828-6].