Graphene growth on bulk substrates : from CVD on SiC to MBE on Ge

Graphene, a single layer of sp2-bonded carbon atoms in a hexagonal lattice, has fascinated scientists since pioneering works by Andre Geim and Walt de Heer's groups in 2004. Graphene's exceptional properties, including high electron mobility and optical transparency, make it promising for various applications in electronics and optoelectronics.This thesis aims to grow graphene on germanium, a substrate that could be used instead of silicon for future electronic devices such as MOSFETs, and which also has the advantage, unlike silicon, of not forming strong bonds with carbon. Two growth methods were studied: chemical vapor deposition (CVD), which is a priori more suitable for production, and molecular beam epitaxy (MBE) to benefit from in-situ monitoring tools. This work began with a study of graphene growth by CVD on the reference substrate, silicon carbide (SiC). Previous work has already highlighted the significant effects of hydrogen during graphene growth, allowing the formation of both a monolayer on a buffer layer or a multilayer on a hydrogenated interface. Here, we have also demonstrated strong effects of hydrogen during cooling, and then developed cooling under argon to avoid them. This allowed us to observe and study the stages of graphene growth on a buffer layer and to demonstrate self-limitation of growth to a monolayer, thus facilitating the growth of uniform graphene films. Finally, we studied how graphene formed on different types of SiC surfaces and offcuts, showing that uniformity and reproducibility were mainly limited by variations in residual misorientation of SiC substrates. On germanium, CVD also allowed the growth of nanometer-sized graphene domains, but optimization of surface preparation and growth did not allow for extending the size of these domains.This work then focused on the growth of graphene on germanium by MBE. Before growing graphene, we developed an appropriate cleaning process for the germanium surface in the MBE chamber. We found that heating the germanium to 600°C effectively removed unwanted oxides and sub-oxides from the surface. However, to ensure an atomically clean surface immediately prior to graphene deposition, we developed a two-step cleaning process based on an initial 30-minute annealing at 750°C, followed by a 5-minute flash annealing conducted at the intended growth temperature. Our research showed that by using growth temperatures of approximately 920°C, which is near the melting point of germanium (937°C), we were able to produce graphene. Transmission Electron Microscopy (TEM) and Raman spectroscopy techniques were used to study the quality of the graphene obtained. While we were able to grow graphene successfully, determining the exact number of graphene layers proved challenging. To improve our results, we used different growth times and temperatures, and found that higher temperatures generally produced better quality graphene, even if our best samples still had some defects. Finally, we tried to grow heterostructures of potential interest for applications such as germanium on top of graphene-capped germanium, which could lead to new ways of making flexible electronic devices, or graphene on SiGe, interesting for photodetector applications.