As and Ga dimers in core-level spectroscopy of S-passivated GaAs(001)

We performed a correlated study of sulfide-passivated GaAs(001) surfaces, using x-ray photoelectron spectroscopy and reflection anisotropy spectroscopy. The reflection anisotropy spectra reveal after desorption of the sulfide overlayer the presence of As and Ga dimers analogous to ones observed on As-decapped surfaces. We identify in the 3d core-level spectra the surface components due to As and Ga dimers: their chemical shifts are -0.28 and -0.35 eV, respectively. We propose an interpretation of the main surface components in the framework of a simple model, based on charge neutrality, electron counting, and electronegativity concepts. (C) 1996 American Institute of Physics.