Effects of surface chemical treatment on the formation of metal GaAs interfaces

We have used synchrotron radiation photoemission spectroscopy to investigate the chemical interactions at metal/GaAs interfaces during deposition of Au and In onto GaAs(100) surfaces that are chemically treated in etching solutions. We determine that there exists a thin native oxide layer on the surface that is treated in H ₂ SO ₄ solution. Au reacts with the oxide overlayer to generate AuGa alloy, but In does not interact appreciably with the oxide overlayer leading to the island growth of the In overlayer at high In coverages. We confirmed (NH ₄ ) ₂ S _x treatment leads to a GaAs surface that is terminated with sulfur. For the Au deposition onto this surface, alloy formation and segregates both at interfacial regions and on metallic overlayers are significantly suppressed, leading to the island growth of the Au overlayer. On the other hand, at initial stages of In deposition, In strongly interacted with the (NH ₄ ) ₂ S _x -treated surface to generate a thin layer of In _x Ga _1-x As alloy on which the In overlayer formed in a layer-by-layer fashion. We also investigate the effects of surface treatments in the Fermi level pinning.