The surface electronic states of clean and hydrogen-terminated ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ surfaces were studied with angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). A series of strained and relaxed ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ 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 ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ alloys. A diffuse double domain 2×1 reconstructed surface was obtained after the H-plasma exposure, which implies that the Si(Ge)-H monohydride domains are smaller than the surface terraces. The diffuse peaks were attributed to disorder and incoherence in the H termination rather than a change of the terrace structure. He I (21.21 eV) and Ne I (16.85 eV) resonance lines were employed to identify the surface states or resonances and bulk states of all samples described in this paper. ARUPS spectra of the series of clean and H-terminated ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ alloys were obtained as a function of emission angle along the [010] direction. From measurements of the series of clean ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ alloy surfaces the surface states or resonances due to the dangling bond and the back bond were identified and found to disperse downward from Γ to ${\mathit{J}}_{\mathit{ab}}^{\prime }$. A nondispersive hydrogen-induced surface state or resonance was observed from the series of H-terminated ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ alloy surfaces. The electron affinities of the series of clean and H-terminated ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ alloy surfaces were also measured using ARUPS. The electron affinity of the Si(100) surface was found to be 3.83 eV and those of strained and relaxed ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ (100) surfaces ranged from 3.87 to 4.05 eV. The electron affinity of clean and H-terminated surfaces exhibited the same values. © 1996 The American Physical Society.

• Received 17 June 1996

DOI:https://doi.org/10.1103/PhysRevB.54.14102