Surface electronic structure of clean and hydrogen-chemisorbe alloy surfaces

The surface electronic states of clean and hydrogen-terminated (Formula presented)(Formula presented) surfaces were studied with angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). A series of strained and relaxed (Formula presented)(Formula presented) alloys were grown on Si(100) wafers using electron-beam evaporation in an ultrahigh-vacuum molecular-beam-epitaxy chamber. The growth was followed by in situ hydrogen-plasma exposure to obtain H-terminated surfaces. After alloy film growth, a double domain 2×1 reconstruction was observed for the series of clean (Formula presented)(Formula presented) alloys. A diffuse double domain 2×1 reconstructed surface was obtained after the H-plasma exposure, which implies that the Si(Ge)-H monohydride domains are smaller than the surface terraces. The diffuse peaks were attributed to disorder and incoherence in the H termination rather than a change of the terrace structure. He I (21.21 eV) and Ne I (16.85 eV) resonance lines were employed to identify the surface states or resonances and bulk states of all samples described in this paper. ARUPS spectra of the series of clean and H-terminated (Formula presented)(Formula presented) alloys were obtained as a function of emission angle along the [010] direction. From measurements of the series of clean (Formula presented)(Formula presented) alloy surfaces the surface states or resonances due to the dangling bond and the back bond were identified and found to disperse downward from Γ to (Formula presented). A nondispersive hydrogen-induced surface state or resonance was observed from the series of H-terminated (Formula presented)(Formula presented) alloy surfaces. The electron affinities of the series of clean and H-terminated (Formula presented)(Formula presented) alloy surfaces were also measured using ARUPS. The electron affinity of the Si(100) surface was found to be 3.83 eV and those of strained and relaxed (Formula presented)(Formula presented) (100) surfaces ranged from 3.87 to 4.05 eV. The electron affinity of clean and H-terminated surfaces exhibited the same values.