The chemical properties of metal/GaAs interfaces formed by the deposition of metals, Au and Ag, onto the GaAs(100) surfaces treated with H2SO4 and (NH4)2Sx solutions, have been investigated using synchrotron-radiation photoemission spectroscopy. Photoemission data demonstrate that As atoms are segregated on the metal overlayer during Au and Ag deposition on GaAs surfaces with native oxide, while the As segregation is suppressed on the (NH4)2Sx-treated GaAs surface which has no native oxide. In the case of Au deposition, we demonstrate that for low coverages of Au the formation of AuGa alloy is suppressed on the (NH4)2Sx-treated surface. The island growth of Ag film and the absence of AgGa alloy during Ag deposition are observed, an indication that no reaction occurs between the Ag and the (NH4)2Sx-treated GaAs substrate. We suggest that the removal of native oxide and sulfur-termination are crucial to the passivation of metal/GaAs interfaces.
