SPACE-CHARGE LAYER, METALLIZATION, AND COLLECTIVE EXCITATIONS OF THE BI GAAS(110) INTERFACE/

The collective excitations and the metallization of the Bi/GaAs(I 10) interface grown at room temperature, up to the completion of a few ten s of a monolayer, have been studied by means of the high-resolution el ectron-energy-loss spectroscopy (HREELS). Through analysis of the HREE LS data, also by means of an appropriate semiclassical dielectric mode l, the modifications experienced by the substrate-related loss structu res (Fuchs-Kliewer phonon and dopant-induced free-carrier plasmon) and by the quasielastic peak are related to changes in the dielectric res ponse of the overlayer and in the semiconductor space-charge region. T he influence of bismuth is effective in enlarging the depletion layer thickness, leaving the interface semiconducting at the monolayer-cover age scale. A band bending value of 0.56 eV is obtained at the coverage of one monolayer on the highly n-type doped sample (n approximately 2 .7 X 10(18) cm-3); a determination free from any possible surface phot ovoltaic effect. At coverages greater than two monolayers, which corre sponds to a structural transition, the intermediate structural phase b ecomes metallic, thus marking a clear semiconductor-metal transition. This intermediate metallic stage further develops towards the formatio n of actual semimetallic crystalline bismuth layers oriented with the basal plane parallel to the substrate surface.