Inelastic electron scattering investigation of the Sb/GaAs(110) system

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Abstract
A high-resolution electron-energy-loss spectroscopy study of the Sb/[n-type GaAs (110)] system grown at room temperature is presented. A very wide range of antimony coverages was exploited (from 0.02 to 200 monolayers). The amorphous-polycrystalline transition accompanied by the semiconductor-metal transition, taking place in the deposited overlayer, was brought into evidence through the analysis of the energy-loss structures related to the electronic and the vibrational excitations of the system in different energy-loss regions. In particular, the intensity change and the energy shift undergone by the substrate’s Fuchs-Kliewer optical phonon, and the intensity modification of the dopant-induced free-carrier plasmon, marked a critical value for 15 monolayers coverage. The band-bending change upon antimony chemisorption has also been estimated from the plasmon-energy position, and an origin for the states inducing the Fermi-level pinning has been suggested. The evolution as a function of coverage of an electronic excitation proper of Sb, which shifts from 90 to 125 meV of loss energy, has been explained as being due to a ‘‘size effect’’ due to the varying overlayer thickness. This result has been obtained through the comparison of the experimental loss function with a model one. Moreover, the dielectric function of antimony has been determined in the 0.045–0.5-eV energy range. The high-resolution electron-energy-loss technique is also presented as a superb probe for the study of the electronic structure of narrow-band-gap surface and interface systems.