Giant Intrinsic Carrier Mobilities in Graphene and Its Bilayer (original) (raw)
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Communications Physics
Pristine graphene and graphene-based heterostructures can exhibit exceptionally high electron mobility if their surface contains few electron-scattering impurities. Mobility directly influences electrical conductivity and its dependence on the carrier density. But linking these key transport parameters remains a challenging task for both theorists and experimentalists. Here, we report numerical and analytical models of carrier transport in graphene, which reveal a universal connection between graphene’s carrier mobility and the variation of its electrical conductivity with carrier density. Our model of graphene conductivity is based on a convolution of carrier density and its uncertainty, which is verified by numerical solution of the Boltzmann transport equation including the effects of charged impurity scattering and optical phonons on the carrier mobility. This model reproduces, explains, and unifies experimental mobility and conductivity data from a wide range of samples and pro...
Physical Review B, 2009
The carrier density and temperature dependence of the Hall mobility in mono-, bi-and tri-layer graphene has been systematically studied. We found that as the carrier density increases, the mobility decreases for mono-layer graphene, while it increases for bilayer/tri-layer graphene. This can be explained by the different density of states in monolayer and bi-layer/tri-layer graphenes. In mono-layer, the mobility also decreases with increasing temperature primarily due to surface polar substrate phonon scattering. In bilayer/tri-layer graphene, on the other hand, the mobility increases with temperature because the field of the substrate surface phonons is effectively screened by the additional graphene layer(s) and the mobility is dominated by Coulomb scattering.
arXiv: Materials Science, 2020
Pristine graphene and graphene-based heterostructures exhibit exceptionally high electron mobility and conductance if their surface contains few electron-scattering impurities. Here, we reveal a universal connection between graphene's carrier mobility and the variation of its electrical conductance with carrier density. Our model of graphene conductivity is based on a convolution of carrier density and its uncertainty, which reproduces the observed universality. Taking a single conductance measurement as input, this model accurately predicts the full shape of the conductance versus carrier density curves for a wide range of reported graphene samples. We verify the convolution model by numerically solving the Boltzmann transport equation to analyse in detail the effects of charged impurity scattering on carrier mobility. In this model, we also include optical phonons, which relax high-energy charge carriers for small impurity densities. Our numerical and analytical results both c...
Temperature-dependent resistivity in bilayer graphene due to flexural phonons
Physical Review B, 2011
We have studied electron scattering by out-of-plane (flexural) phonons in doped suspended bilayer graphene. We have found the bilayer membrane to follow the qualitative behavior of the monolayer cousin. In the bilayer, different electronic structure combine with different electron-phonon coupling to give the same parametric dependence in resistivity, and in particular the same temperature T behavior. In parallel with the single layer, flexural phonons dominate the phonon contribution to resistivity in the absence of strain, where a density independent mobility is obtained. This contribution is strongly suppressed by tension, and in-plane phonons become the dominant contribution in strained samples. Among the quantitative differences an important one has been identified: room T mobility in bilayer graphene is substantially higher than in monolayer. The origin of quantitative differences has been unveiled.
Limits on Charge Carrier Mobility in Suspended Graphene due to Flexural Phonons
Physical Review Letters, 2010
The temperature dependence of the mobility in suspended graphene samples is investigated. In clean samples, flexural phonons become the leading scattering mechanism at temperature T * 10 K, and the resistivity increases quadratically with T. Flexural phonons limit the intrinsic mobility down to a few m 2 =V s at room T. Their effect can be eliminated by applying strain or placing graphene on a substrate.
Electron and Phonon Transport in Graphene in and out of the Bulk
NanoScience and Technology, 2013
Carbon atoms have the unique capability of associating with each other in different ways at the macro-and nanoscopic scales to form various architectures, some of them being unique. Following the discovery of fullerenes, these last twentyfive years witnessed the discovery of some new forms of carbon atom associations leading to a large diversity of nanocarbons with fascinating properties. As regards bulk carbons, the decade preceding the discovery of fullerenes paved the way for finding some physical properties which were found later to be displayed in these new nano entities. This mainly concerns the semiclassical and, more particularly, the quantum aspects of two-dimensional (2D) electronic transport and the behavior of phonons in low-dimensional materials. These effects are discussed here in relation to the electrical and thermal conductivities of various nano-carbon based materials. This chapter also reflects the obvious similarities and differences observed in the transport properties of an isolated single layer graphene out of the bulk (SLG), or a few layers of graphene out of the bulk (FLG), supported or suspended, and those of a single (stage-1) or more (stage-n, where n = 2, 3, . . .) of these carbon layer planes sandwiched between planes formed by other chemical species, as is the case for macroscopic graphite intercalation compounds (GICs), and more particularly quasi
Graphite in the bilayer regime: In-plane transport
An interplay between the increase in the number of carriers and the decrease in the scattering time is expected to result in a saturation of the in-plane resistivity, ab , in graphite above room temperature. Contrary to this expectation, we observe a pronounced increase in ab in the interval between 300 and 900 K. We provide a theory of this effect based on intervalley scattering of charge carriers by high-frequency, graphenelike optical phonons.
Physical Review Letters, 2010
Transport and elastic scattering times, tr and e , are experimentally determined from the carrier density dependence of the magnetoconductance of monolayer and bilayer graphene. Both times and their dependences on carrier density are found to be very different in the monolayer and the bilayer. However, their ratio tr = e is found to be close to 1.8 in the two systems and nearly independent of the carrier density. These measurements give insight on the nature (neutral or charged) and range of the scatterers. Comparison with theoretical predictions suggests that the main scattering mechanism in our samples is due to strong (resonant) scatterers of a range shorter than the Fermi wavelength, likely candidates being vacancies, voids, adatoms or short-range ripples.
Universality of transport through graphene-on-substrate
By investigating low-temperature transport through many graphene devices on hBN substrates, we reveal a clear correlation between the carrier mobility mu\mumu and the width of the resistance peak around charge neutrality. The correlation -satisfied quantitatively also by devices realized in other laboratories and on other substrates- indicates that a same, universal microscopic mechanism limits the carrier mobility and generates charge fluctuations for graphene-on-substrate. Weak-localization measurements show that the underlying random disorder potential is long-ranged, at least for devices whose mobility is between 1.000 and 80.000 cm$^2$/Vs. We propose a theoretical interpretation based on the effects of strain in graphene, which reproduces all key aspects of our observations.