Défense de thèse de doctorat en sciences physiques : "Graphene on Si"

Direct growth of graphitic carbon/graphene on Si(111) substrate by using electron beam evaporation

Jury

Jean-Marc THEMLIN (Univ. Aix-Marseille), Jacques DUMONT (UCL), Olivier DEPARIS (UNamur), Laurent HOUSSIAU, président (UNamur), Robert SPORKEN, promoteur (UNamur)

Résumé

Graphene has recently emerged as a promising material due to its outstanding electrical, optical, thermal, and mechanical properties. It opens new possibilities not only for fundamental physics research but also for industrial applications. Nowadays, since silicon is still the most important single-crystal substrate used for semiconductor devices and integrated circuits, integration of graphene into the current Si technology is highly desirable. A combination between graphene and silicon may overcome the traditional limitations in scaling down of devices that silicon-based technology is facing. Graphene on Si might be one of the most promising candidates as a material for graphene-based technology beyond CMOS. Therefore, it is crucial to find a process to grow graphene directly on Si.

In this thesis, we chose Si(111) as a substrate for graphene formation by electron beam evaporation because its surface has an interesting multi-layer reconstruction driven by the minimization of dangling bonds at the surface compared with other oriented Si. It exhibits a six-fold symmetry and is the most stable surface among various orientations of Si. Therefore, it is expected to be an appropriate substrate for graphitic carbon growth. However, due to the huge lattice mismatch between graphene (a_G = 2.46 Å) and Si(111) (a_Si(1×1) = 3.84 Å), it is not easy to grow directly graphene on Si(111) and a buffer is considered as a solution to reduce the lattice mismatch. In this context, we have proposed a structural model using amorphous carbon (a-C) and/or SiC as a buffer on Si(111) with different configurations such as C/a-C/Si(111), C/a-C/3C-SiC/Si(111), C/3C-SiC/Si(111) or C/Si/3C-SiC/Si(111) (C stands for the graphitic layer). The quality of the graphitic layer depends not only on the substrate temperature but also on the growth time and on the thickness of the buffer layer. In addition, we also found that silicon diffuses through the SiC buffer layer during the graphene growth and reduces the quality of epitaxial graphene. Therefore, a calculation of the silicon diffusion profile through the SiC buffer layer during carbon deposition is presented to explain how the crystalline quality of graphene depends on the details (annealing temperature, growth time, etc.) of the growth process.

La défense est publique.

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