Electronic structure and Schottky-barrier formation of Ag on n-type GaAs(110)

The electronic structure and Schottky-barrier formation of the Ag/[cleaved n-type GaAs(110)] interface are studied at room temperature by using ultraviolet and x-ray photoemission spectroscopy. It is found that more metal coverage is needed to pin the surface Fermi level with Ag than with most other metals. The Schottky barrier is resolved as 0.830.1 eV high (compared to 0.900.1 eV for Cu/[n-type GaAs(110)] and 0.920.1 eV for Au/[n-type GaAs(110)]). At the early stage of Ag deposition, the so-called atomiclike Ag 5s states and Ag 3d core levels are observed, which may imply that the interaction between Ag and GaAs is weak and raises the possibility that the Ag atoms may form clusters during the initial stages of metal deposition. It is found that the Ag valence-band photoyield has a maximum at a coverage of 1030 A. This photoyield enhancement is explained in terms of Ag clustering and the Stranski-Kristanov growth pattern. In the framework of the unified defect model, it is proposed that the heat released due to the Ag-Ag interaction is responsible for the creation of the defect levels which pin the Fermi level in the Ag/[n-type GaAs(110)] interface. Thus, defects are produced under the clusters but not on the open GaAs surfaces not covered by Ag; this leads to the increased amount of metal needed to complete the surface Fermi-level pinning.