Electronic and atomic structure of the 6H-SiC(0001) surface studied by ARPES, LEED, and XPS

We present an investigation of the electronic and geometric structure of the carbon terminated 6H-SiC(000 (1) over bar) surface. The samples were prepared in different ways that result in the same unreconstructed (1x1) surface. From angle-resolved photoemission spectra taken along the <(Gamma)over bar> (M) over bar and the <(Gamma)over bar> (K) over bar azimuth, the strong dispersion of a surface state in the ionic gap and of a bulk state at the boundary of the ionic gap is measured. This indicates unambiguously that large areas of the surface are well Ordered. The comparison with band-structure calculations shows that even these areas do not have the properties of an intrinsic 6H-SiC(000 (1) over bar) surface. From a low-energy electron diffraction (LEED) structure analysis of the same surface a model is determined with domains of all three possible bilayer truncations of the bulk unit cell present at the surface with equal weight. For the well-ordered parts of the surface the combination of LEED and core-level x-ray photoemission spectroscopy (XPS) favors a geometry with hydrogen adatoms bonded to the topmost carbon atoms of the first bilayer thus saturating the surface dangling bonds. However, the XPS data also show that the applied sample treatment does not yield a surface that is completely free of oxygen contamination, which must be located in the disordered parts of the surface.