Using complementary surface analysis techniques, we study the Ge growth on distinct SiC(0 0 0 1) reconstructions and elucidate complex mechanisms occurring by thermal activation. Two Si-rich reconstructions, (3 × 3) and , and one C-rich, , are concerned, on which Ge is found to grow in Stranski–Krastanov and Volmer–Weber modes, respectively. The best Ge-wetting layer is favoured on the (less Si-rich) because closest to a perfect truncated SiC(0 0 0 1) termination. At sufficiently high temperature, the Ge-wetting layer is organized in the form of a (4 × 4)Ge reconstruction for which we propose a first atomic model that is based on the 3 × 3 structure. Annealing Ge on the (3 × 3) and surfaces provokes spectacular successive 2D/3D and unusual 3D/2D transitions not only of Ge but also of Si and C, respectively, coming from the surface initial richness. In both cases, a phase separation is observed either in the 2D or 3D structures, which is unexpected for the Ge/Si binary system and somewhat usual for the Ge/C one. In the case of Ge on , a special 2D heterostructure graphite/Ge/SiC is achieved at the atomic level. This acts as a Schottky barrier and then can be promising for future possible applications.

High temperature annealing of 4H-or 6H-SiC͑0001͒ crystals is well known to desorb Si from the surface and to generate a C-rich ͑6 ͱ 3 ϫ 6 ͱ 3͒R30°͑6 ͱ 3͒ 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-͑1 ϫ 1͒ 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 graphite͑6 ͱ 3͒ / SiC or graphite͑1 ϫ 1͒ / 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 ͑ϳ1.2 eV͒ of the n-doped SiC, making this second interface to act as a Schottky barrier. Above 1300°C, a delayed Ge desorption takes place that allows the graphite sheets to reform in their initial 6 ͱ 3 form, i.e., without Ge and with flatter bands.

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