CS-INDUCED HIGHEST E(F) JUMP ABOVE INAS(110) CONDUCTION-BAND MINIMUM

Upon room-temperature deposition of minute amounts of Cs on InAs(110) surfaces, one induces probably the highest Fermi-level pinning positio n (almost-equal-to 0.6 eV) for a semiconductor above the conduction-ba nd minimum. Synchrotron-radiation core-level photoemission spectroscop y was used to follow the Fermi-level movement from the shift of the In 4d and As 3d core levels as a function of Cs coverages at room temper ature. Already at very low coverages the Fermi level reaches an extrem ely high maximum above the conduction-band minimum. The maximum of the Fermi-level position correlates fairly well with the ionization energ y of the individual atoms, as expected in the framework of the theory of donor-type surface states induced by metallic adatoms. We thus cons ider that individual Cs adatoms produce donor-type surface states plac ed at almost-equal-to 0.6 eV above the conduction-band minimum. This i nduces a very strong downward band bending which suggests the existenc e of a two-dimensional electron gas at the open, nearly clean InAs(110 ) surface.