High-Velocity Saturation in Graphene Encapsulated by Hexagonal Boron Nitride

Yamoah, Megan; Yang, Wenmin; Pop, Eric; Goldhaber‐Gordon, David

doi:10.1021/acsnano.7b03878

Cited by 101 publications

(99 citation statements)

References 45 publications

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“…The mechanism for this apparent Ohmic I-V characteristics in the Dirac limit is different from the conventional Drude model in that the linear dependence of the electric field comes from the nonequilibrium charge density instead of the drift velocity. This linear JE relation without saturation close to the Dirac point has been observed in clean graphene encapsulated by the hexa-boron-nitrides 27,46 . Away from the Dirac charge-neutrality point, the conventional Boltzmann transport is recovered with the tendency for the current saturation with where the drift velocity is proportional to ω ph /n 1/2 eq with the equilibrium charge density n eq .…”

Section: Discussionsupporting

confidence: 70%

Nonequilibrium excitations and transport of Dirac electrons in electric-field-driven graphene

Han

2018

Phys. Rev. B

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We investigate nonequilibrium excitations and charge transport in charge-neutral graphene driven with dc electric field by using the nonequilibrium Green's function technique. Due to the vanishing Fermi surface, electrons are subject to non-trivial nonequilibrium excitations such as highly anisotropic momentum distribution of electron-hole pairs, an analog of the Schwinger effect. We show that the electron-hole excitations, initiated by the Landau-Zener tunneling with a superlinear IV relation I ∝ E 3/2 , reaches a steady state dominated by the dissipation due to optical phonons, resulting in a marginally sublinear IV with I ∝ E, in agreement with recent experiments. The linear IV starts to show the sign of current saturation as the graphene is doped away from the Dirac point, and recovers the semi-classical relation for the saturated velocity. We give a detailed discussion on the nonequilibrium charge creation and the relation between the electron-phonon scattering rate and the electric field in the steady-state limit. We explain how the apparent Ohmic IV is recovered near the Dirac point. We propose a mechanism where the peculiar nonequilibrium electron-hole creation can be utilized in an infra-red device.

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Section: Discussionsupporting

confidence: 70%

Nonequilibrium excitations and transport of Dirac electrons in electric-field-driven graphene

Han

2018

Phys. Rev. B

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“…Figure 6b shows the calculated MR for µ varied from 1000 to 20,000 cm 2 V −1 s −1 with n 0 and B set equal to 1 × 10 11 cm −2 and 2 T, respectively. The MR peak value increases dramatically with µ, reaching nearly 1600% as µ approaches 20,000 cm 2 V −1 s −1 , a mobility representative of that for high-quality graphene on h-BN 26,27 . Figure 6a, b shows that, in contrast to Hall sensitivity, the key to achieving high MR in graphene is having a high µ rather than a low n 0.…”

Section: Cnp Is the Charge Neutrality Pointmentioning

confidence: 93%

Operation of graphene magnetic field sensors near the charge neutrality point

2019

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Graphene is a promising material for sensing magnetic fields via the Hall effect due to its atomic-scale thickness, ultra-high carrier mobilities and low cost compared to conventional semiconductor sensors. Because of its Dirac band structure, graphene sensors differ from semiconductor sensors in that both electrons and holes participate in the carrier transport. This two-channel transport complicates the sensor operation and causes performance tradeoffs that demand careful examination. Here, we examine the operation of graphene sensors operated near the charge neutrality point (CNP) where two-channel transport prevails. We find that, while the largest magnetoresistance occurs exactly at the CNP, the maximum realizable Hall sensitivities occur away from the CNP and depend on linearity constraints and power limitations. In particular, a more stringent linearity constraint reduces the realizable sensitivities for mobilities above a critical value µ c , which scales with magnetic field.

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“…T HE two-dimensional material graphene is a promising candidate for application in high-frequency devices due to its high charge carrier saturation velocity [1]. Until recently, the realization of graphene field-effect transistors (GFETs) for high-frequency electronics was hindered by extrinsic limitations caused by impurities that reduced the carrier velocity, large extrinsic source/drain contact resistances, and large pad capacitances [2]- [5].…”

Section: Introductionmentioning

confidence: 99%

Graphene Field-Effect Transistors With High Extrinsic <inline-formula> <tex-math notation="LaTeX">${f}_{T}$</tex-math> </inline-formula> and <inline-formula> <tex-math notation="LaTeX">${f}_{\mathrm{max}}$</tex-math> </inline-formula>

Bonmann

Asad

Yang

et al. 2019

IEEE Electron Device Lett.

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In this work, we report on the performance of graphene field-effect transistors (GFETs) in which the extrinsic transit frequency (f T) and maximum frequency of oscillation (fmax) showed improved scaling behavior with respect to the gate length (Lg). This improvement was achieved by the use of high-quality graphene in combination with successful optimization of the GFET technology, where extreme low source/drain contact resistances were obtained together with reduced parasitic pad capacitances. GFETs with gate lengths ranging from 0.5 µm to 2 µm have been characterized, and extrinsic f T and fmax frequencies of up to 34 GHz and 37 GHz, respectively, were obtained for GFETs with the shortest gate lengths. Simulations based on a small-signal equivalent circuit model are in good agreement with the measured data. Extrapolation predicts extrinsic f T and fmax values of approximately 100 GHz at Lg=50 nm. Further optimization of the GFET technology enables fmax values above 100 GHz, which is suitable for many millimeter wave applications.

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High-Velocity Saturation in Graphene Encapsulated by Hexagonal Boron Nitride

Cited by 101 publications

References 45 publications

Nonequilibrium excitations and transport of Dirac electrons in electric-field-driven graphene

Nonequilibrium excitations and transport of Dirac electrons in electric-field-driven graphene

Operation of graphene magnetic field sensors near the charge neutrality point

Graphene Field-Effect Transistors With High Extrinsic <inline-formula> <tex-math notation="LaTeX">${f}_{T}$</tex-math> </inline-formula> and <inline-formula> <tex-math notation="LaTeX">${f}_{\mathrm{max}}$</tex-math> </inline-formula>

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