SURFACE-STATE BAND-STRUCTURE OF THE SI(100)2X1 SURFACE STUDIED WITH POLARIZATION-DEPENDENT ANGLE-RESOLVED PHOTOEMISSION ON SINGLE-DOMAIN SURFACES

The electronic structure of the Si(100)2×1 surface has been studied with polarization-dependent angle-resolved photoemission. By using vicinal Si(100) samples, single-domain 2×1 surfaces were obtained, and the surface-band dispersions were measured unambiguously along the symmetry axes -J and J in the surface Brillouin zone (SBZ). The obtained dispersions are compared to dispersions from earlier studies of two-domain surfaces, as well as to theoretical band-structure calculations. In addition to the well-known surface state attributed to the dangling bonds, five more surface-related structures were observed on the single-domain surface. One of these is the controversial surface state previously observed on two-domain surfaces at J in the [010] direction at 0.9 eV below the Fermi level (EF), which is not accounted for in any calculated surface band structure for the Si(100)2×1 surface. Contrary to a previous report, it is also observed on the single-domain surface at several points in the SBZ. The second additional structure was found to disperse downwards along the -J line, to a minimum energy of 3.4 eV below EF at J. It is interpreted as a back-bond resonance. The third additional structure was seen as a faint peak at the Fermi level in normal emission. Finally, two other surface-related structures were found in the -J direction, one at -1.3 eV at in the second SBZ, splitting into two peaks for higher k values. By using a linearly polarized light source, the symmetry properties of the surface states and resonances were determined along the symmetry axes -J and -J in the SBZ. The polarization dependence for several states indicates a mirror symmetry along these directions, with the dangling-bond state having even parity in both directions, in agreement with theoretical predictions for symmetric dimer models, and the back-bond resonance having odd parity in the -J direction. Three of the surface states and resonances are not accounted for in theoretical band structures for the 2×1-reconstruction. Two of these can be explained by domains of asymmetric dimers, arranged into c(4×2) or p(2×2) periodicities. © 1990 The American Physical Society.