Graphene on the cubic silicon carbide
In short: We applied a high temperature process to grow graphene on cubic silicon carbide (3C-SiC). No buffer layer was observed for the graphene grown on the (001) plane, as confirmed by low energy electron microscopy (LEEM) and diffraction (LEED). The cubic symmetry of 3C-SiC leads to a lack of spontaneous polarization, as confirmed by the mild n-doping (n = 7.4×1011cm−2) observed in graphene grown on the (111) plane by angle-resolved photoelectron spectroscopy (ARPES). We demonstrated from different aspects that 3C-SiC is a good substrate for growth of epitaxial graphene. The 3C-SiC samples were grown in a well-controlled process for high crystalline quality without foreign polytype inclusions.
We present the combination of a high temperature process for the graphene production with a newly developed substrate of (001)-oriented cubic silicon carbide (3C-SiC). Characterization is performed by low energy electron microscopy, diffraction and photoelectron angular distribution measurements as well as X-ray photoemission spectroscopy. All our experimental results consistently indicate successful growth of a buffer free few layer graphene on a cubic silicon carbide surface. In literature it has been shown that no buffer layer seems to form at the interface between the (001) crytsal plane of 3C-SiC and the graphene. If a buffer layer was present, it should – due to the reconstruction of the interface – produce superstructure spots in the measured diffraction patterns. Most samples show no superstructure spots at all (Fig. a). Other significant indicator of a missing buffer layer is the X-ray photoemission data. In all spectra of carbon 1s electrons, the typical signal caused by the buffer layer is missing beside the visible signal of the graphene layer itself (Fig. b). Measurements with higher energy allowed probing into the substrate material to make sure that the buffer would be within measurement range, but also here no signal could be found (Fig. c).
We also investigated multilayer epitaxial graphene and quasi-freestanding graphene (QFG) on the silicon-face of different polytypes of hexagonal and cubic silicon carbide (4H-, 6H, and 3C-SiC(111)). The hole concentration was observed to depend on the SiC polytype, in the characteristic manner predicted by the polarization doping model. 4H-SiC, which has the largest spontaneous polarization, induces the largest carrier concentration in QFG, followed by 6H-SiC whose polarization and induced hole concentration are approximately 1.5 times smaller. 3C-SiC(111), which has no spontaneous polarization, induces only a negligible n-type doping (n = 7.4×1011 cm−2) in QFG. This small residual n-doping for graphene on cubic silicon carbide is presumably due to bulk doping, i.e. depletion of the n-type SiC substrate. The experiments provide strong evidence in favor of the polarization doping model. This model also provides a roadmap for the choice of substrates for QFG. Clearly, 3C-SiC would be the substrate material of choice because it allows the lowest charge carrier concentration. As we demonstrated from different aspect that 3C-SiC is a good substrate for growth of epitaxial graphene, we introduced a 3C-SiC growth concept on off-oriented 4H-SiC substrates using sublimation epitaxial method, which allowed us to obtain high crystalline quality 3C-SiC samples without foreign polytype inclusions. The 3C-SiC domains initially nucleate on an in-situ formed large terrace with on-axis surface and subsequently laterally enlarges along the step-flow direction until a complete surface coverage with 3C-SiC is obtained. In such way, a significant reduction of DPBs compared to the cubic polytype growth using the on-axis substrates is achieved.
Details of the research are described in the following three journal articles:
- Swedish Governmental Agency for Innovation Systems (Vinnova)
- Swedish Energy Agency
- Graphene Flagship (European Union Seventh Framework Programme)
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Last updated: 02/13/15