A Core Level and Valance Band Photoemission Study of 6H-SiC(0001)

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The results of a photoemission study of the C terminated 6H-SiC surface, prepared by ex-situ chemical treatment and in-situ heatings, are presented and discussed. The as-introduced unreconstructed 1×1 surface shows strong oxygen-derived features that persist up to a heating temperature of about 950°C. After heating at 1050°C, a 3×3 reconstructed surface is formed, and the valence band spectra show the two subbands in the density of states of SiC. This surface shows a semiconducting behavior since no or very little emission is observed close to or at the Fermi level. Recorded high-resolution C 1s and Si 2p spectra show the presence of one type of Si sites and at least three different C sites in the surface region. Two of these C 1s components are clearly surface related, and the 3×3 reconstruction is therefore suggested to originate from at least two carbon layers on top of a bulk truncated crystal. Heating at 1200°C, is shown to result in a strong enrichment of carbon in the surface region. Recorded core level spectra then show the presence of a graphite C 1s peak but also of other shifted components, which suggest quite large compositional modifications in the surface region.