# 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  
#### 4.1.1 Induced Pseudo-Charge Due to Substrate Polarization Effect  
As described by the ARPES results summarized in Section 2, EG on SiC(0001) exhibits an \(\mathbf{E_{\mathrm{F}}}\) is quite large, which indicates considerable n-type doping. Although some density functional theory (DFT) calculations imply this result, the physical reasons have been clarified by the experimental work of [PERSON] et al. and [PERSON] et al. [75; 81]. The doping originates from three effects and, in some cases, existing simultaneously: (i) polarization induced pseudo-charge due to the hexagonal nature of 6H-SiC and 4H-SiC substrates, (ii) surface states associated with C and Si dangling bonds overlaid on the broad density of states (DOS) of the buffer layer, which act as donor states (part of the [PERSON] model [82]), and (iii) the effect of space-charge layer in (doped) SiC or Si substrates due to band bending at the interface. Figure 8 illustrates these effects. The referenced works [75; 81] demonstrate these reasons are in reasonable agreement with the experiment, especially for hydrogen intercalated graphene (see Section 5.1).  
The implications of this understanding are significant. (1) Preparing EG on a defect-free interface of SiC (0001) should result in n-type doping. (2) EG on 3C-SiC should lead to n-doped graphene layers--modified only by the induced effects of substrate donor states. (3) Varying the hexagonality of the substrate will change the doping. This has been successfully tested using 4H-SiC and 6H-SiC [75].  
The spontaneous polarization has been reported as a bulk property of hexagonal semiconductor compounds, which leads to a polarization charge on the polar surface of SiC, independent to any interface formation [75; 81]. This is induced at the inversion of the stacking sequence of the hexagonal double layers while it is absent in the 3C-SiC polytype due to the symmetry [75]. The spontaneous polarization generates a pseudo acceptor layer with a pseudo charge density (Figure 8) depending on the hexagonal polytype [75]. [PERSON] et al. demonstrated that the sign and magnitude of SiC polarization agree with the charge concentration of H-intercalated graphene on SiC(0001) [81]. The hexagonality of the SiC affects the polarization proportionally, i.e., for the 4H-SiC(0001) the polarization is 6/4 times  
Figure 8: Sketch and band diagram for monolayer EG on SiC(0001). Blue and red circles indicate Si and C atoms, respectively. The polarization is shown at the bottom. The negative polarization related to the discontinuity of the interface polarization is a pseudo charge (marked in circles). D indicates the electrostatic potential between the EG and SiC. The band bending details have been taken from Reference [83]. Adapted with permission from Reference [81]. Copyright (2012) American Physical Society.  
larger than that for the 6H-SiC(0001) [75, 81] and, as mentioned above, has been shown experimentally via the H-intercalation (Section 5.1).