# Electronic and Transport Properties of Epitaxial Graphene on SiC and 3C-SiC/Si: A Review
## 5 Fine-Tuning of Transport Properties
### Intercalation  
Intercalation has been performed via different elements such as hydrogen [21; 75; 77; 81; 134], oxygen [78], fluorine [135], gold [136], and magnesium [43]. The monolayer graphene formed after intercalation of buffer layer on SiC (0001) is called quasi-free-standing monolayer graphene (QFMLG). [PERSON] et al. [134] produced QFMLG by annealing the buffer layer on Si-face SiC(0001) in atmospheric pressure H\({}_{2}\). The XPS C 1s and Si 2p spectra demonstrated that H saturate the Si dangling bonds and decouples the buffer layer by forming a monolayer graphene [134]. Buffer layer decoupling in EG on 3C-SiC (111) via H-intercalation has also been demonstrated [21; 76]. The QFMLG on SiC (0001) films measured by ARPES are generally p-type doped [75] (see Figure 17). As discussed in Section 4.1.1, [PERSON] et al. and [PERSON] et al. determined that the p-type conduction of QFMLG is caused by the spontaneous polarization of the SiC [75; 81]. QFMLG layers formed on semi-insulating 4H-SiC (0001) indicated a hole concentration of \(8.6\times 10^{12}\) cm\({}^{-2}\) (stronger spontaneous polarization of 4H-SiC) extracted from the Fermi surface measurement [75] at \(\mathbf{E_{\mathrm{F}}}\) 340 meV below the \(\mathbf{E_{\mathrm{D}}}\), whereas the QFMLG on 6H-SiC (0001) exhibits a p-type carrier concentration of \(5.5\times 10^{12}\) cm\({}^{-2}\) with \(\mathbf{E_{\mathrm{F}}}\) 300 meV below the \(\mathbf{E_{\mathrm{D}}}\). The Fermi velocity was measured to be \(0.98\times 10^{6}\) ms\({}^{-1}\)[75; 33]. [PERSON] et al. demonstrated that the mobility of QFMLG showed reduced temperature dependence compared with an as-grown MLG, which indicates reduced scattering from the underlying SiC (see Figure 18). The mobility of MLG falls by more than 50% when the temperature is increased from 25 K to 300 K whereas the change in mobility is only \(\sim\) 10% for the QFMLG across the same temperature range (samples indicated constant carrier concentration across the entire temperature range). The weak temperature dependence of mobility, approaching the behavior exhibited by flakes (see Section 4.5) signifies QFMLG is effectively decoupled from substrate compared to MLG [129]. Furthermore, for T greater than 290 K, the mobility of QFMLG are generally 3-5 times larger than EG before H-intercalation (Figure 18). The production of quasi-free-standing bilayer graphene by H-intercalation of MLG has also been achieved [77; 137]. Reference [77] reported H-intercalated BLG  
Figure 17: ARPES band structure of QFMLG formed on (**a**) 6H SiC, (**b**) 4H-SiC, and (**c**) 3C-SiC. Reprinted with permission from Reference [75]. Copyright (2014) IOP Publishing Ltd.  
with a p-type carrier concentration of \(10^{12}\) cm\({}^{-2}\) with \(\mathbf{E_{\mathrm{F}}}\) 230 meV below the \(\mathbf{E_{\mathrm{D}}}\). The Fermi velocity was measured to be \(1.04\times 10^{6}\) ms\({}^{-1}\). In contrast to the p-type polarization doping of QFMLG on bulk SiC substrates, the ARPES data of QFMLG on 3C-SiC (111) by H-intercalation reported slight n-type doping (see Figure 17c). This is due to the absence of spontaneous polarization in 3C-SiC [75]. The n-type doping density of about \(10^{12}\) cm\({}^{-2}\) was estimated, which was related to the residual defects at the interface [76]. [PERSON] et al. reported that the p-type transport properties of EG on 3C-SiC (111) did not improve after decoupling the buffer layer, which confirms that the interface silicates dominate the transport properties in this instance. The intercalation process has also attempted via an oxidation process for EG on SiC (0001). [PERSON] et al. [78] demonstrated that, through an oxidation process, the oxygen saturates Si dangling bonds and breaks some Si-C bonds of the buffer layer. In this case, the buffer layer is only partially decoupled, and the resulting sample had molecular oxygen intercalated between carbon layers with a (\(\sqrt{3}\times\sqrt{3}\)) rotated \(30^{\circ}\) pattern as observed with uLEED.