Synchrotron x-ray photoelectron spectroscopy study of hydrogen-terminated 6H-SiCˆ0001‰ surfaces

We report on highly resolved core-level and valence-band photoemission spectroscopies of hydrogenated, unreconstructed 6H-SiC(0001) and (0001̄) using synchrotron radiation. In the C 1s core level spectra of 6H-SiC(0001̄) a chemically shifted surface component due to C-H bonds is observed at a binding energy (0.4760.02) eV higher than that of the bulk line. The Si 2p core-level spectra of SiC(0001) suggest the presence of a surface component as well but a clear identification is hindered by a large Gaussian width, which is present in all spectra and which is consistent with values found in the literature. The effect of thermal hydrogen desorption was studied. On 6H-SiC(0001) the desorption of hydrogen at 700–750 °C is accompanied by a simultaneous transformation to the Si-rich (A33A3)R30° reconstruction. On 6H-SiC(0001̄) first signs of hydrogen desorption, i.e., the formation of a dangling bond state in the fundamental band gap of SiC, are seen at temperatures around 670 °C while the (131) periodicity is conserved. At 950 °C a (333) reconstruction is formed. The formation of these reconstructions on thermally hydrogenated 6H-SiC(0001) and (0001̄) is discussed in the light of earlier studies of 6H-SiC$0001% surfaces. It will be shown that by using the hydrogenated surfaces as a starting point it is possible to gain insight into how the (A33A3)R30° and (333) reconstructions are formed on 6H-SiC(0001) and 6H-SiC(0001̄), respectively. This is due to the fact that only hydrogen-terminated 6H-SiC$0001% surfaces possess a surface carbon to silicon ratio of 1:1.