ATOMIC NITROGEN ON INAS(110) SURFACES AT ROOM-TEMPERATURE

The interaction of atomic nitrogen with cleaved InAs(110) surfaces at room temperature was investigated by using a Kelvin probe and photoemission spectroscopy excited with Mg(Kalpha), Zr(Mzeta) as well as monochromatic He I and He II radiation. The increase of the N(1s) signal by a simultaneous decrease of the As(3s) intensity accompanied by a constant In(3d5/2) signal indicates an anion exchange. An N-induced build-up of inversion layers was found on samples doped p-type and of accumulation layers on those doped n-type. For larger exposures the Fermi level becomes pinned at 0.58 eV above the top of the valence band at the surface irrespective of the type of doping. This energy position of the Fermi level agrees very well with the charge-neutrality level of the virtual gap states. With increasing nitrogen exposure two new components to the In(4d) core-level spectra were observed which are chemically shifted by 0.23 and 0.64 eV to larger binding energies with respect to the bulk component. With the As(3d) level a component shifted by 2.1 eV to larger binding energies was detected. All shifts are caused by bonds with nitrogen. The ionization energy initially decreases but increases for larger exposures. The minimum occurs at an N-coverage of one monolayer. It is explained by the removal of the relaxation and a build-up of two additional surface dipoles.