Structural and electronic properties of epitaxial graphene on SiC(0 0 0 1): a review of growth, characterization, transfer doping and hydrogen intercalation

Abstract

To cite this version:C Riedl, C Coletti, U Starke. Structural and electronic properties of epitaxial graphene on SiC(0001): a review of growth, characterization, transfer doping and hydrogen intercalation. Journal of Physics D: Applied Physics, IOP Publishing, 2010, 43 (37) Abstract.Graphene, a monoatomic layer of graphite hosts a two-dimensional electron gas system with large electron mobilities which makes it a prospective candidate for future carbon nanodevices. Grown epitaxially on silicon carbide (SiC) wafers, large area graphene samples appear feasible and integration in existing device technology can be envisioned. This article reviews the controlled growth of epitaxial graphene layers on SiC(0001) and the manipulation of their electronic structure. We show that epitaxial graphene on SiC grows on top of a carbon interface layer that -although it has a graphite-like atomic structure -does not display the linear π-bands typical for graphene due to a strong covalent bonding to the substrate. Only the second carbon layer on top of this interface acts like monolayer graphene. With a further carbon layer, a graphene bilayer system develops. During the growth of epitaxial graphene on SiC(0001) the number of graphene layers can be precisely controlled by monitoring the π-band structure. Experimental fingerprints for in-situ growth control could be established. However, due to the influence of the interface layer, epitaxial graphene on SiC(0001) is intrinsically n-doped and the layers have a long-range corrugation in their density of states. As a result, the Dirac point energy where the π-bands cross is shifted away from the Fermi energy, so that the ambipolar properties of graphene cannot be exploited. We demonstrate methods to compensate and eliminate this structural and electronic influence of the interface. We show that the band structure of epitaxial graphene on SiC(0001) can be precisely tailored by functionalizing the graphene surface with tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) molecules. Charge neutrality can be achieved for mono-and bilayer graphene. On epitaxial bilayer graphene, where a band gap opens due to the asymmetric electric field across the layers imposed by the interface, the magnitude of this band gap can be increased up to more than double of its initial value. The hole doping allows the Fermi level to shift into the energy band gap. The impact of the interface layer can be completely eliminated by decoupling the graphene from the SiC substrate by a hydrogen intercalation technique. We demonstrate that hydrogen can migrate under the interface layer and passivate the underlying SiC substrate. The interface layer alone transforms into a quasi-free standing monolayer. Epitaxial monolayer graphene turns into a decoupled bilayer. In combination with atmospheric pressure graphitization, the intercalation process allows to produce quasi-free standing epitaxial graphene on large SiC wafers and represents a highly promising route towards epitaxial graphene based nanoelectronics.Confidential: ...

Spatial extent of a Landauer residual-resistivity dipole in graphene quantified by scanning tunnelling potentiometry

“…Samples with epitaxial mono-and bilayer graphene are prepared by thermal decomposition of n-doped 6H-SiC(0001) 30 at T ¼ 1400-1600°C under ultra-high vacuum (UHV, 10 À 10 mbar).The samples (2 mm  7 mm) are electrically contacted ex situ with gold contacts of 100 nm thickness by thermal evaporation through a shadow mask. After reinsertion into the UHV chamber, the samples are heated up to 350°C for 30 min to eliminate surface contaminations before they are transferred in situ to a homebuilt lowtemperature scanning tunnelling microscope.…”

Changes in work function due to NO2 adsorption on monolayer and bilayer epitaxial graphene on SiC(0001)

“…The clean graphene layer on SiC is strongly n doped, with the experimental Dirac point located 0.45 eV below the Fermi level [10]. The band structure associated with NO 2 adsorbed on this 1LG/SiC surface is shown in Fig.…”

“…The first carbon layer to form is covalently bonded to the SiC substrate, and does not display the electronic features characteristic of graphene. Subsequent carbon layers are strongly n doped due to the influence of this carbon buffer layer [9,10,10,11]. There have been several successful experimental studies of using graphene grown on SiC as a NO 2 sensor [3,4,[12][13][14][15][16].…”

Quasi-free-standing monolayer and bilayer graphene growth on homoepitaxial on-axis 4H-SiC(0 0 0 1) layers

“…Although the Al2O3 layer is amorphous due to the deposition method, it serves quite well as an initial passivation layer. Furthermore, the sample is uniformly p-type which is expected from hydrogen intercalation [31,36]. Overall, the SI SiC control represents a high quality control by which to gauge the overall electrical characteristics of epitaxial graphene grown on SiC epi-layers.…”