Electronic and structural analysis of Sb-induced GaAs(100)(2x4) and (2x8) surfaces

Electronic and structural properties of Sb-induced GaAs(100)(2x4) and (2x8) surfaces are studied by means of core-level and valence-band photoelectron spectroscopy utilizing synchrotron radiation and scanning tunneling microscopy. Combining these results and showing good consistency among them, we demonstrate that the Sb/GaAs(100)(2x4) surface is well compatible with the delta structural model, which includes one Sb dimer in both the first and third atomic layers and two second-layer Ga dimers per unit cell (i.e., the Sb coverage of 0.5 ML), giving experimental support to generality of the delta-type model for III-V(100)(2x4) surfaces, proposed previously on the basis of ab-initio calculations. Deconvolution of the Sb 4d core-level spectrum from the (2x4) surface shows two components, which are tentatively connected to two inequivalent Sb-dimer sites in the delta unit cell. Angle-resolved valence-band photoelectron spectroscopy reveals Sb-induced surface-derived states at near 0.4 and 0.6 eV below the valence-band maximum (VBM) for the Sb/GaAs(100)(2x4) surface, which have not been found in earlier measurements. These two surface-derived features mapped along symmetry lines of the surface Brillouin zone are identified with previous electronic-structure calculations. The results are also compared to band-structure measurements of the As/GaAs(100)(2x4) surface found in the literature. For the Sb/GaAs(100)(2x8) surface, we propose a structural model which, in contrast to the recent model, obeys the electron counting rule and consists of Sb dimers in three atomic layers, showing the Sb coverage of 1.25 ML for the (2x8) surface. The Sb 4d core-level spectrum from this surface exhibits three components, which are discussed within the determined structural model. The valence-band measurements of the (2x8) surface propose a new Sb-induced surface state at near 0.5 eV below the VBM