# 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)  
Thermal decomposition of SiC in vacuum or argon atmosphere is the well-established process for producing graphene on SiC [56, 75, 5, 84]. Electronic and transport properties of EG on SiC depends upon the type of surface termination of SiC (Si-face or C-face). Although both Si and C sublimate, the Si flux is dominant. The differences between the graphitic layer grown on the Si-face (0001) and the C-face (0001) were first reported by [PERSON] et al. [85]  
Graphene grown on SiC(0001) possesses a carbon-rich amorphous interfacial layer (\(6\sqrt{3}\times 6\sqrt{3}\)) rotated 30\({}^{\circ}\)[86] known as the buffer layer in between the SiC and graphene [31]. The buffer layer forms strong covalent bonds with the SiC. The electronic structure of the buffer layer shows a large gap and an \(\mathbf{E_{F}}\) pinned by a state with a small dispersion close to the conduction band (see Figure 9) [31]. These states are related to the dangling bonds in the buffer layer. When more than one carbon layer is present, the graphene-related dispersions are recovered. [PERSON] et al. used ARPES measurements to study the band structure changes starting from the 6\(\sqrt{3}\) surface of SiC. The interaction of the buffer layer with the 6\(\sqrt{3}\) surface results in a \(\sigma\)-band instead of a \(\pi\)-band. Continued sublimation converts the buffer layer into graphene with \(\pi\)-band [86] and simultaneously creates a new buffer layer underneath. As-grown MLG on Si-face SiC is generally reported to be electron-doped with a carrier concentration of \(\sim\)\(1\times 10^{13}\) cm\({}^{-2}\)[26, 37, 82], 300 K mobility of \(\sim\)1000 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\), and a 25 K mobility of \(\sim\)2000 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\)[26] [55]. The n-type conductivity is due to the charge transfer from donor-like states at the EG/SiC interface, i.e., the buffer layer, that overcompensates the spontaneous polarization of SiC [81], as discussed in Section 4.1.1. The band structure for BLG on SiC(0001) was calculated using DFT by [PERSON] et al. [31] and is in agreement with the ARPES results by [PERSON] et al. [33, 34]. Additional details are in Section 2.2. The \(\mathbf{E_{F}}\) is \(\sim\)250-400 meV above the Dirac point (n-type conductivity), which is slightly lower than that for epitaxial monolayers. This is likely due to charge transfer from the buffer layer [31], whose cause likely has some similarity with the effects discussed in Section 4.1.1. The carrier concentration \(\approx 5\times 10^{12}\) cm\({}^{-2}\)[65] and the mobility is \(\sim\)1000 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\)[45]. The lower \(\mathbf{E_{F}}\) and doping level of BLG may indicate a weaker substrate interaction as reported by [PERSON] et al. [34]  
#### Impact of Growth on SiC (0001)  
Unlike the graphene on SiC (0001), graphene formation on SiC (0001) does not involve a buffer layer at the EG-SiC interface. This is because a different surface reconstruction occurs. [PERSON] et al. [87] analyzed the atomic structure of the (\(2\times 2\)) reconstruction on (0001) SiC using an in situ prepared  
Figure 9: Dispersion curves for a buffer layer. Adapted with permission from Reference [31]. Copyright (2007) American Physical Society. samples and quantitative LEED intensity analysis. In this case, \(\frac{3}{4}\) of the carbon atoms on the (0001) surface plane are bonded to a silicon adatom in a hollow site with two dangling bonds (Si adatom and C rest atom) [5]. Using first-principles, [PERSON] et al. calculated the band structure incorporating the (2 \(\times\) 2) surface reconstruction (see Figure 10a) [5] and claimed that the electronegativity difference between silicon and carbon induces a charge transfer from the Si adatom to the C rest atom that forms surface states in the electronic band structure EG on SiC(000\(\overline{1}\)) (see Figure 10b) [31]. This results in pinning of the Fermi energy, which makes the samples n-type. Yet, [PERSON] et al. and [PERSON] et al.