Bidimensional intercalation of Ge between SiC(0001) and a heteroepitaxial graphite top layer -: art. no. 115319

High temperature annealing of 4H- or 6H-SiC(0001) crystals is well known to desorb Si from the surface and to generate a C-rich (6 root 3x6 root 3)R30 degrees (6 root 3) reconstruction explained as a graphite monolayer in heteroepitaxial registry with the substrate. Ge deposition at room temperature and in the monolayer range on this graphitized reconstruction results in Ge islands. Using a number of surface techniques, we follow subsequent Ge morphology evolutions as a function of isochronal post-annealing treatments at increasing temperatures. In a particular temperature window Ge reacts with the substrate by diffusion under the graphite planes and wets the Si-terminated SiC surface. In spite of this bidimensional insertion of a Ge layer, the epitaxial relationship between the SiC substrate and the graphite is maintained as shown by very clear graphite-(1x1) LEED or RHEED patterns. They denote extended and well-ordered graphite planes at the surface of a graphite/Ge/SiC heterostructure. XPS analyses reveal a complete passivation of the intercalated Ge layer against oxidation by the overlying graphite sheets. Moreover, drastic spectroscopic changes on the bulk-SiC Si 2p and C 1s core levels are observed, depending on whether graphite(6 root 3)/SiC or graphite(1x1)/Ge/SiC terminations are analyzed. In the latter case, the observed core level splitting of the bulk components is interpreted by a significant upward band bending (similar to 1.2 eV) of the n-doped SiC, making this second interface to act as a Schottky barrier. Above 1300 degrees C, a delayed Ge desorption takes place that allows the graphite sheets to re-form in their initial 6 root 3 form, i.e., without Ge and with flatter bands.