Core level and valence band photoemission experiments coupled to theoretical calculations reveal the formation of a stoichiometric Ge–Au phase during gold deposition onto Ge(111) at room temperature. This result is significantly different with respect to that found for the Si–Au system.

We used photoemission spectroscopy with synchrotron radiation to investigate the formation and the microscopic properties of interfaces between semiconducting substrates and Si overlayers deposited by electron bombardment. The main goal of the experiment was to measure the valence band discontinuity in these systems and test the limits of the discontinuity transitivity rule predicted by all ‘‘linear’’ models. This rule could be tested by combining our present data on Si overlayers and previous data on Ge overlayers on Si, GaAs, and CdS. We found that the rule is valid for the above interfaces only within an accuracy of a few tenths of an electron volt. Our results are in agreement with recent evidence that the Harrison LCAO approach, one of the ‘‘linear’’ models, predicts the valence band discontinuities with an accuracy of the order of ∼0.25 eV.

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Photoemission results on the interface formation process for In on cleaved GaAs(110) are completely at odds with respect to those on other III–V/metal interfaces. We do not observe the transition between an ultralow coverage (<0.1 monolayer) ‘‘chemisorption’’ stage and an intermediate coverage (0.1–2 monolayer) ‘‘clustering’’ stage, observed for Al overlayers. Also for Al overlayers, the transition corresponds to the onset of a cation exchange reaction and to the pinning of the Fermi level. The exchange reaction is not observed for GaAs(110)–In, and the Fermi-level pinning occurs at much larger coverages. Furthermore, the pinning position for n-type GaAs is not the canonical one observed for a wide variety of metal, semiconductor, and oxygen overlayers, but 0.2–0.25 eV above it. All of these ‘‘odd’’ results demonstrate that the kinetics of the interface formation is a fundamental factor in the defect model, and clarify its role.

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