# Electronic and Transport Properties of Epitaxial Graphene on SiC and 3C-SiC/Si: A Review
## 4 Electronic and Transport Properties: Effect of Interactions with the Surroundings
### Epitaxial Graphene-Substrate Interaction
#### Impact of Growth on SiC (0001)
argue the situation is more complex due to the hexagonal nature of the substrate (see Section 4.1.1) even though n-type behaviour is still predicted. This situation is clarified by detailed experimental work, which will be described below. The graphene layers on the C-face are thicker and randomly rotated against each other as well as with respect to the substrate [86; 88] and, thus, exhibit weaker interactions with the substrate [86; 48]. This unusual rotational stacking causes multilayers of graphene on the C-face to have an electronic structure similar to that of the monolayer graphene [8; 35; 88] with a well-defined Dirac cone (linear dispersion) near the charge neutrality point [22]. Shubnikov-de Haas oscillations were observed using Hall bars, which indicated that the transport layer has a Berry phase of \(\pi\), similar to that of a single layer graphene. This signified that it is electronically decoupled from the layer above it [89]. Additional evidence for the decoupling is found in ARPES data of the multilayer EG (MEG) stack, which reveals the decoupled nature of the layers [35; 48] in contrast to ARPES results on Bernal BLG on Si-face, where Dirac cones remain unperturbed and distinct from one another [90]. Infrared spectroscopy measurements shows \(\mathbf{E_{\mathrm{F}}}\sim\)8 meV, doping \(\sim\)10\({}^{10}\) cm\({}^{-2}\), and low magnetic field mobility \(\sim\)10\({}^{6}\) cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\)[91]. Room temperature transport measurements reported on these MEG on C-face SiC samples are typically p-type [5] with sheet density of \(\sim\)10\({}^{13}\)-10\({}^{14}\) cm\({}^{-2}\) and mobility of \(\sim\)1000-3000 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\) even though a wide range of values and even n-type measurements have been reported [72; 73; 74; 14; 56; 75; 76; 77; 78; 79]. This seems to run counter to the n-type predictions noted in Section 4.1.1, which we will address next. This difficulty of measured p-type properties vs. the n-type prediction situation is explained by considering the work of [PERSON] et al. [14] who performed variable magnetic field Hall measurements on a series of samples. The data was best fit to a model where three types of transport regions exist in the layers of the sample: the layers closest to the substrate (substrate interaction), the interior layers (nearly neutral), and then the outer layers (ambient interaction). Each region has distinct sheet density and mobility. The epitaxial layer that lies closest to the SiC is highly electron-doped with high conductivity  
Figure 10: (**a**) EG/SiC(000\(\overline{1}\)) interface with the (2 \(\times\) 2) C surface reconstruction. Si adatoms and C rest atoms are marked. Adapted with permission from Reference [5]. Copyright (2012) AIP Publishing. (**b**) Electronic band structure of EG on SiC(000\(\overline{1}\) ). Adapted with permission from Reference [31]. Copyright (2007) American Physical Society. (\(10^{12}\) cm\({}^{-2}\), 12,400 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\)). This is consistent with the models of [PERSON] and [PERSON] [75, 81]. The model is also supported by an ultrafast optical spectroscopy measurement that resulted in a doping density of \(9\times 10^{12}\) cm\({}^{-2}\) corresponding to a Fermi level of \(\sim\)350 meV above the Dirac point for the layer close to the substrate [72]. The second transport region is nearly intrinsic (p-type, \(5\times 10^{11}\) cm\({}^{-2}\), 20,000 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\)) due to charge screening. Additional support for this can be found, for example, from Landau level spectroscopy where the results are expected to be dominated by sample regions having high mobility [90]. Measurements of MEG have resulted in exceptionally high room temperature mobilities (\(>\)200,000 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\)) consistent with nearly intrinsic doping [48, 50, 93, 94].