The physics of epitaxial graphene on SiC(0001)

Abstract

Various physical properties of epitaxial graphene grown on SiC(0001) are studied. First, the electronic transport in epitaxial bilayer graphene on SiC(0001) and quasi-free-standing bilayer graphene on SiC(0001) is investigated. The dependences of the resistance and the polarity of the Hall resistance at zero gate voltage on the top-gate voltage show that the carrier types are electron and hole, respectively. The mobility evaluated at various carrier densities indicates that the quasi-free-standing bilayer graphene shows higher mobility than the epitaxial bilayer graphene when they are compared at the same carrier density. The difference in mobility is thought to come from the domain size of the graphene sheet formed. To clarify a guiding principle for controlling graphene quality, the mechanism of epitaxial graphene growth is also studied theoretically. It is found that a new graphene sheet grows from the interface between the old graphene sheets and the SiC substrate. Further studies on the energetics reveal the importance of the role of the step on the SiC surface. A first-principles calculation unequivocally shows that the C prefers to release from the step edge and to aggregate as graphene nuclei along the step edge rather than be left on the terrace. It is also shown that the edges of the existing graphene more preferentially absorb the isolated C atoms. For some annealing conditions, experiments can also provide graphene islands on SiC(0001) surfaces. The atomic structures are studied theoretically together with their growth mechanism. The proposed embedded island structures actually act as a graphene island electronically, and those with zigzag edges have a magnetoelectric effect. Finally, the thermoelectric properties of graphene are theoretically examined. The results indicate that reducing the carrier scattering suppresses the thermoelectric power and enhances the thermoelectric figure of merit. The fine control of the Fermi energy position is thought to be key for the practical use of graphene as a thermoelectric material, which could be achieved with epitaxial graphene. All of these results reveal that epitaxial graphene is physically interesting.

Growth of epitaxial graphene: Theory and experiment

“…In order to investigate the role of SiC steps in supplying excess C atoms to the surface, Kageshima et al [377] also simulated several possible growth scenarios at the steps using again a series of simple relaxation calculations as shown in Fig. 87.…”

Theoretical Study of Graphene on SiC(11-20) a-Face

“…Such a buffer layer, however, is not observed for the C-face [42][43][44][45][46]. According to our previous theoretical studies, the graphene formation on the Si-face obeys the interfacial formation mechanism [39,62,63]. New graphene sheets always grow from the interface between the old graphene sheets and the SiC substrate.…”

“…We employ the first-principles calculation with plane wave bases, ultrasoft pseudopotentials, and the density functional as our previous studies [39,[60][61][62][63][64][65][66][67][68][69]. We use the cutoff of the plane waves of 25 Ry and the exchange-correlation functional of the generalized gradient approximation [70].…”

“…Epitaxial graphene grown on silicon carbide (SiC) surface is attractive because it is formed directly on an insulating substrate [17,18]. Graphene is traditionally grown on SiC(0001) Si-face [16,18,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] or (0001) C-face [22,[40][41][42][43][44][45][46]. Graphene on Si-face is known to have epitaxial relation with the substrate, while that on C-face is randomly stacked.…”

Unveiling the carrier transport mechanism in epitaxial graphene for forming wafer-scale, single-domain graphene

“…clear contrast to our previous report where we have shown only crystallographic single crystallinity in graphene through LRGT due to the uncertainty of the quality of graphene near the terrace edges of SiC (26). Further elimination of the process residues during the LRGT leads to a notable maximum mobility of 7,496 cm 2 /V·s measured at room temperature for a single-crystalline, singledomain graphene transferred on a SiO 2 /Si substrate, which supersedes as the highest value ever reported from graphene formed on the Si face of an SiC wafer (15,16,(21)(22)(23)(27)(28)(29).…”