Observation of Interface States by High-Resolution Electron-Energy-Loss Spectroscopy in Metal-GaAs(110) Junctions

Ag, Au, and In/GaAs (110) interfaces have been investigated by high-resolution electron-energy-loss spectroscopy, ultraviolet photoemission spectroscopy, and x-ray photoemission spectroscopy. Energy-loss peaks at 0.72 and 1.2 eV-that is, in the GaAs energy gap region-have been detected at the early stage of the junction formation. The intensity behavior of the 1.2-eV feature, as a function of metal coverage, strictly follows the evolution of the total perimeter of the metal islands. Similar features have been also found on cleaved stepped surfaces. These facts suggest that the loss structures are due to transitions among defect states induced by the metal overlayer and localized at the interface.