Formation of metal-semiconductor interfaces on MBE-grown gallium arsenide(100): Surface photovoltage, chemistry and band bending

The chemical, structural and electronic properties of the metal-GaAs interfaces formed on the polar (100) surface are studied using high resolution core level photoemission spectroscopy (PES) and low energy electron diffraction (LEED). The clean (4 x 2)-c(8 x 2) reconstructed GaAs(100) surface, prepared by molecular beam epitaxy and subsequent thermal decapping of an As protective layer, is characterized carefully. Ga 3d and As 3d core levels are analyzed using test square curve fitting. Two Ga surface components are resolved while only one surface component is necessary for As. The assignment of these surface components to different surface atomic arrangements is discussed. The surface Fermi level position with respect to the valence band maximum is also investigated as a function of decapping temperature.; Metal (In, Ga, Au)/GaAs(100) interfaces, formed at both room (RT) and low temperature (LT), are studied. The morphology of these interfaces resembles that of metal/GaAs(110) interfaces formed at LT, in that the deposited metal atoms reside at the surface as isolated adatoms rather than as clusters at submonolayer coverage. Metal clustering is only important at coverages higher than a few monolayers and is more prominent at RT than at LT. The GaAs(100) band bending is studied as a function of metal coverage and deposition temperature. At submonolayer metal coverages, In and Ga both cause reduced band bending ({dollar}sim{dollar}0.2eV) on n-type GaAs, a phenomenon similar to the Fermi level overshoot observed at LT-formed metal/p-GaAs(110) interfaces and indicative of formation of adatom-induced donor levels in the upper part of the band gap. With Au, In and Ga, the Fermi level is pinned at 0.4eV, 0.6eV and 0.68eV above the valence band maximum respectively, in good agreement with the results obtained at metal/GaAs(110) interfaces. This contradicts recent claims of near-Schottky limit for these interfaces. Evidence of correlation between pinning and overlayer metallization is found for all three interfaces, supporting the metal induced gap states (MIGS) model for Schottky barrier formation.; The synchrotron radiation-induced surface photovoltage (SPV), which could invalidate the apparent band bending measured with PES, is studied as a function of metal coverage and temperature, using a Kelvin probe. A large (0.55eV) and quasi-permanent SPV is observed on lightly doped n-GaAs at LT. A non-negligible (0.2eV) SPV is also observed at room temperature. No SPV is detected on highly doped GaAs. The impact of this synchrotron radiation induced SPV on the photoemission study of metal-semiconductor interfaces is discussed.