Top-gated graphene field-effect-transistors formed by decomposition of SiC (original) (raw)
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Electronic Structure of Epitaxial Graphene Layers on SiC: Effect of the Substrate
Physical Review Letters, 2007
Recent transport measurements on thin graphite films grown on SiC show large coherence lengths and anomalous integer quantum Hall effects expected for isolated graphene sheets. This is the case eventhough the layer-substrate epitaxy of these films implies a strong interface bond that should induce perturbations in the graphene electronic structure. Our DFT calculations confirm this strong substrate-graphite bond in the first adsorbed carbon layer that prevents any graphitic electronic properties for this layer. However, the graphitic nature of the film is recovered by the second and third absorbed layers. This effect is seen in both the (0001)and (0001) 4H SiC surfaces. We also present evidence of a charge transfer that depends on the interface geometry. It causes the graphene to be doped and gives rise to a gap opening at the Dirac point after 3 carbon layers are deposited in agreement with recent ARPES experiments (T.Ohta et al, Science 313 (2006) 951).
High Electron Mobility in Epitaxial Trilayer Graphene on Off-axis SiC(0001)
Scientific Reports, 2016
The van de Waals heterostructure formed by an epitaxial trilayer graphene is of particular interest due to its unique tunable electronic band structure and stacking sequence. However, to date, there has been a lack in the fundamental understanding of the electronic properties of epitaxial trilayer graphene. Here, we investigate the electronic properties of large-area epitaxial trilayer graphene on a 4° off-axis SiC(0001) substrate. Micro-Raman mappings and atomic force microscopy (AFM) confirmed predominantly trilayer on the sample obtained under optimized conditions. We used angle-resolved photoemission spectroscopy (ARPES) and Density Functional Theory (DFT) calculations to study in detail the structure of valence electronic states, in particular the dispersion of π bands in reciprocal space and the exact determination of the number of graphene layers. Using far-infrared magnetotransmission (FIR-MT), we demonstrate, that the electron cyclotron resonance (CR) occurs between Landau levels with a (B) 1/2 dependence. The CR line-width is consistent with a high Dirac fermions mobility of ~3000 cm 2 •V −1 •s −1 at 4 K. Monolayer graphene is a two-dimensional materials with linear dispersions near the K and K' points of the Brillouin zone. Low-energy charge carriers therein obey the Dirac-Weyl equation and behave like massless fermions 1. This material is ambipolar and exhibits ballistic transport properties on a micrometer scale up to room temperature. In multilayer graphene, the interlayer coupling introduces perturbations of the low-energy band dispersions 2. Consequently, the linear π and π* bands near the Fermi level in monolayer graphene are modified in multilayer graphene, showing a strong dependence on the stacking sequence as well as the layer number. Recently multilayer graphene has attracted considerable interest 3 due to the possibility of inducing a band gap. This band gap can be generated by breaking the translational symmetry using an external electric field 4,5 or by introducing asymmetrical doping between the graphene layers resulting in a 'built in' electric field 3,6. Moreover, the number of graphene layers and their stacking configuration will control the electronic properties of multilayer graphene. When multilayer graphene are stacked, Bernal stacking represents the lowest energy configuration. The shift of one atom of the bottom layer along the CC bond axis (one bond length) allows a transition between the Bernal and the second stable allotropes of multilayer graphene, rhombohedral stacking. In the case of trilayer graphene, this transition has to overcome, an energy barrier of about 1.1 meV/atom 7. A viable method for obtaining a large-scale graphene production is the epitaxial approach based on SiC graphitization. The epitaxial growth of graphene on semi-insulating SiC has the potential to enable the next generation of ultra high frequency and low power electronic devices. The main advantage here is the possibility of obtaining a large graphene area directly on semi-insulating substrates which is one of the main requirements for high frequency devices, with a huge control of the number of graphene layers. Moreover, the choice of the appropriate SiC polytype also makes it possible to select for the formation of Bernal or rhombohedral multilayer graphene 8. Other methods to obtain large-area graphene include chemical vapor deposition (CVD) on metals 9. However, this CVD on metal process is less suitable for device manufacture, as the graphene layers must be transferred onto a semiconducting substrate. These transferred graphene layers tend to acquire contamination as a result of the transfer process, thus
Electronic and Transport Properties of Epitaxial Graphene on SiC and 3C-SiC/Si: A Review
Applied Sciences
The electronic and transport properties of epitaxial graphene are dominated by the interactions the material makes with its surroundings. Based on the transport properties of epitaxial graphene on SiC and 3C-SiC/Si substrates reported in the literature, we emphasize that the graphene interfaces formed between the active material and its environment are of paramount importance, and how interface modifications enable the fine-tuning of the transport properties of graphene. This review provides a renewed attention on the understanding and engineering of epitaxial graphene interfaces for integrated electronics and photonics applications.
Epitaxial graphene transistors on SiC substrates
2008
Graphene holds great promise for future electronic technology. It has very high mobility even for thin films, and is compatible with high-k dielectrics. Thus while it is too early to speculate on graphene replacing silicon as the material of choice for electronics, the potential of carbon based devices should not be underestimated.
Journal of physics. Condensed matter : an Institute of Physics journal, 2015
The electrical transport properties of epitaxial graphene layers are correlated with the SiC surface morphology. In this study we show by atomic force microscopy and Raman measurements that the surface morphology and the structure of the epitaxial graphene layers change significantly when different pretreatment procedures are applied to nearly on-axis 6H-SiC(0 0 0 1) substrates. It turns out that the often used hydrogen etching of the substrate is responsible for undesirable high macro-steps evolving during graphene growth. A more advantageous type of sub-nanometer stepped graphene layers is obtained with a new method: a high-temperature conditioning of the SiC surface in argon atmosphere. The results can be explained by the observed graphene buffer layer domains after the conditioning process which suppress giant step bunching and graphene step flow growth. The superior electronic quality is demonstrated by a less extrinsic resistance anisotropy obtained in nano-probe transport exp...
SiC Substrate effects on electron transport in the epitaxial graphene layer
Electronic Materials Letters, 2014
Hall effect measurements on epitaxial graphene (EG) on SiC substrate have been carried out as a function of temperature. The mobility and concentration of electrons within the two-dimensional electron gas (2DEG) at the EG layers and within the underlying SiC substrate are readily separated and characterized by the simple parallel conduction extraction method (SPCEM). Two electron carriers are identified in the EG/SiC sample: one highmobility carrier (3493 cm 2 /Vs at 300 K) and one low-mobility carrier (1115 cm 2 /Vs at 300 K). The high mobility carrier can be assigned to the graphene layers. The second carrier has been assigned to the SiC substrate.
Scientific Reports, 2014
We investigate the magneto-transport properties of epitaxial graphene single-layer on 4H-SiC(0001), grown by atmospheric pressure graphitization in Ar, followed by H 2 intercalation. We directly demonstrate the importance of saturating the Si dangling bonds at the graphene/SiC(0001) interface to achieve high carrier mobility. Upon successful Si dangling bonds elimination, carrier mobility increases from 3 000 cm 2 V -1 s -1 to > 11 000 cm 2 V -1 s -1 at 0.3 K. Additionally, graphene electron concentration tends to decrease from a few 10 12 cm -2 to less than 10 12 cm -2 . For a typical large (30 × 280 µm 2 ) Hall bar, we report the observation of the integer quantum Hall states at 0.3 K with well developed transversal resistance plateaus at Landau level fillings factors of ν = 2, 6, 10, 14… 42 and Shubnikov de Haas oscillation of the longitudinal resistivity observed from about 1 T. In such a device, the Hall state quantization at ν=2, at 19 T and 0.3 K, can be very robust: the dissipation in electronic transport can stay very low, with the longitudinal resistivity lower than 5 mΩ, for measurement currents as high as 250 µA. This is very promising in the view of an application in metrology.
Low Carrier Density Epitaxial Graphene Devices On SiC
Small (Weinheim an der Bergstrasse, Germany), 2015
The transport characteristics of graphene devices with low n- or p-type carrier density (∼10(10) -10(11) cm(-2) ), fabricated using a new process that results in minimal organic surface residues, are reported. The p-type molecular doping responsible for the low carrier densities is initiated by aqua regia. The resulting devices exhibit highly developed ν = 2 quantized Hall resistance plateaus at magnetic field strengths of less than 4 T.