Epitaxial graphene growth on silicon carbide (SiC) by thermal decomposition is a method to produce large-scale few-layer graphene (FLG). Graphene is one of the most promising nanomaterials for the future because of its various characteristics, like strong stiffness and high electric and thermal conductivity. Still, reproducible production of Graphene is difficult, thus many different techniques have been developed. The main advantage of epitaxial graphene growth on silicon carbide over other techniques is to obtain graphene layers directly on a semiconducting or semi-insulating substrate which is commercially available.^{[1] [2]}

The thermal decomposition of bulk SiC was first reported in 1965 by Badami. He annealed the SiC in vacuum to around 2180 °C for an hour to obtain a graphite lattice.^[3] In 1975, Bommel et al. then achieved to form monolayer graphite on the C-face as well as the Si-face of hexagonal SiC. The experiment was carried out under UHV with a temperature of 800 °C and hints for a graphene structure could be found in LEED patterns and the change in the carbon Auger peak from a carbide character to a graphite character. ^{[4] [5]} New insights in the electronic and physical properties of graphene like the Dirac nature of the charge carriers, half-integer quantum Hall effect or the observation of the 2D electron gas behaviour were first measured on multilayer graphene from de Heer et al. at the Georgia Institute of Technology in 2004.^[6][7] Still, the Nobel Prize in Physics ″for groundbreaking experiments regarding the two-dimensional material graphene″ in 2010 was awarded to Andre Geim and Konstantin Novoselov. An official online document of the Royal Swedish Academy of Sciences about this awarding got under fire. Walter de Heer mentions several objections about the work of Geim and Novoselov who apparently have measured on many-layer graphene, also called graphite, which has different electronic and mechanical properties.^[8] Emtsev et al. improved the whole procedure in 2009 by annealing the SiC-samples at high temperatures over 1650 °C in an argon environment to obtain morphologically superior graphene.^[9]

The underlying process is the desorption of atoms from an annealed surface, in this case a SiC-sample. Due to the fact that the vapor pressure of carbon is negligible compared to the one of silicon, the Si atoms desorb at high temperatures and leave behind the carbon atoms which form graphitic layers, also called few-layer graphene (FLG). Different heating mechanisms like e-beam heating or resistive heating lead to the same result. The heating process takes place in a vacuum to avoid contamination. Approximately three bilayers of SiC are necessary to set free enough carbon atoms needed for the formation of one graphene layer. This number can be calculated out of the molar densities.^[10] Today's challenge is to improve this process for industrial fabrication. The FLG obtained so far has a non-uniform thickness distribution which leads to different electronic properties. Because of this, there's a demand for growing uniform large-area FLG with the desired thickness in a reproducible way. Also, the impact of the SiC substrate on the physical properties of FLG is not totally understood yet.^[1]

The thermal decomposition process of SiC in high / ultra high vacuum works out well and appears promising for large-scale production of devices on graphene basis. But still, there are some problems that have to be solved. Using this technique, the resulting graphene consists of small grains with varying thickness (30–200 nm). These grains occur due to morphological changes of the SiC surface under high temperatures. On the other side, at relatively low temperatures, poor quality occurs due to the high sublimation rate.^[2]

The growth procedure was improved to a more controllable technique by annealing the SiC-samples at high temperatures over 1650 °C in an argon environment. ^[11][9] The desorbed silicon atoms from the surface collide with the argon atoms and a few are reflected back to the surface. This leads to a decrease of the Si evaporation rate.^[12] Carrying out the experiment under high temperatures further enhances surface diffusion. This leads to a restructuring of the surface which is completed before the formation of the graphene layer.^[2] As an additional advantage, the graphene domains are larger in size than in the initial process (3 x 50 μm²) up to 50 x 50 μm² .^{[13] [14]}

Of course, the technology always undergoes changes to improve the graphene quality. One of them is the so-called confinement controlled sublimation (CCS) method. Here, the SiC sample is placed in a graphite enclosure equipped with a small leak. By controlling the evaporation rate of the silicon through this leak, a regulation of the graphene growth rate is possible. Therefore, high-quality graphene layers are obtained in a near-equilibrium environment.^{[7] [15]} The quality of the graphene can also be controlled by annealing in the presence of an external silicon flux. By using disilane gas, the silicon vapor pressure can be controlled.^[16]

SiC is bipolar and therefore the growth can take place on both the SiC(0001) (silicon-terminated) or SiC(0001) (carbon-terminated) faces of 4H-SiC and 6H-SiC wafers. The different faces result in different growth rates and electronic properties.

To optimize the growth conditions, it is important to know the number of graphene layers. This number can be determined by using the quantized oscillations of the electron reflectivity. Electrons have a wave character. If they are shot on the graphene surface, they can be reflected either from the graphene surface or from the graphene-SiC interface. The reflected electrons (waves) can interfere with each other. The electron reflectivity itself changes periodically as a function of the incident electron energy and the FLG thickness. For example, thinner FLG provides longer oscillation periods. The most suitable technique for these measurements is the low-energy electron microscopy (LEEM).^[1]

A fast method to evaluate the number of layers is using optical microscope in combination with contrast-enhancing techniques. Single-layer graphene domains and substrate terraces can be resolved on the surface of SiC.^[23] The method is particularly suitable for quick of the surface.

Furthermore, epitaxial graphene on SiC is considered as a potential material for high-end electronics. It is considered to surpass silicon in terms of key parameters like feature size, speed and power consumption and is therefore one of the most promising materials for future applications.

Limitations in terms of wafer sizes, wafer costs and availability of micromachining processes have to be taken into account when using SiC wafers.^[2]

Another problem is directly coupled with the advantage. of growing the graphene directly on a semiconducting or semi-insulating substrate which is commercially available. But there's no perfect method yet to transfer the graphene to other substrates. For this application, epitaxial growth on copper is a promising method. The carbon's solubility into copper is extremely low and therefore mainly surface diffusion and nucleation of carbon atoms are involved. Because of this and the growth kinetics, the graphene thickness is limited to predominantly a monolayer. The big advantage is that the graphene can be grown on Cu foil and subsequently transferred to for example SiO₂.^[26]

• Carbide-derived carbon