Graphitization of the 6H-SiC(0001) surface as a function of annealing temperature has been studied by ARPES, high resolution XPS, and LEED. For the initial stage of graphitization – the 6√3 reconstructed surface – we observe σ-bands characteristic of graphitic sp2-bonded carbon. The π-bands are modified by the interaction with the substrate. C1s core level spectra indicate that this layer consists of two inequivalent types of carbon atoms. The next layer of graphite (graphene) formed on top of the 6√3 surface at TA=1250°C-1300°C has an unperturbed electronic structure. Annealing at higher temperatures results in the formation of a multilayer graphite film. It is shown that the atomic arrangement of the interface between graphite and the SiC(0001) surface is practically identical to that of the 6√3 reconstructed layer.

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We report on highly resolved core-level and valence-band photoemission spectroscopies of hydrogenated, unreconstructed 6H-SiC(0001) and (0001 ) using synchrotron radiation. In the C 1s core level spectra of 6H-SiC(0001 ) a chemically shifted surface component due to C-H bonds is observed at a binding energy (0.47Ϯ0.02) 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 (ͱ3ϫͱ3)R30°reconstruction. On 6H-SiC(0001 ) 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 (1ϫ1) periodicity is conserved. At 950°C a (3ϫ3) reconstruction is formed. The formation of these reconstructions on thermally hydrogenated 6H-SiC (0001) and (0001 ) is discussed in the light of earlier studies of 6H-SiC͕0001͖ surfaces. It will be shown that by using the hydrogenated surfaces as a starting point it is possible to gain insight into how the (ͱ3ϫͱ3)R30°and (3ϫ3) reconstructions are formed on 6H-SiC(0001) and 6H-SiC(0001 ), respectively. This is due to the fact that only hydrogen-terminated 6H-SiC͕0001͖ surfaces possess a surface carbon to silicon ratio of 1:1.

Al 2 O 3 films were deposited as alternative gate dielectric on hydrogen-terminated 6H-SiC(0001) by atomic layer chemical vapor deposition and characterized by photoelectron spectroscopy (PES) and admittance measurements. The PES results indicate an abrupt interface free of significant Si–suboxide contributions where the Al2O3 layer is connected to SiC by bridging oxygen atoms. The admittance measurements yield an interface state density which is lower than that of the thermally formed oxide and show in particular no increase toward the conduction band edge. Furthermore, a nearly symmetrical band alignment of Al2O3 on 6H-SiC with offsets of 2.2 and 1.8 eV is determined for the valence and conduction bands, respectively. This makes Al2O3 a serious competitor to thermal oxides as gate insulator in SiC devices.