A transfer technique for high mobility graphene devices on commercially available hexagonal boron nitride

Zomer, P. J.; Dash, Sasmita; Tombros, N.; Wees, van Bart

doi:10.1063/1.3665405

Cited by 357 publications

(314 citation statements)

References 14 publications

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“…For example, samples with the commonly used SiO 2 substrate replaced by hexagonal boron nitride (h-BN) which has a lattice constant very close to that of graphene and an almost atomically flat surface with strongly reduced disorder, 12,13 have shown highly improved transport characteristics with mobilities approaching that of suspended graphene. 8,14,15 Furthermore, the high energy of the surface-optical phonons of h-BN results in a significant reduction of surface-optical phonon scattering [16][17][18] that for commonly used gate oxides starts to dominate the mobility around T ∼ 150-200 K. 5,7 When the mobility is dominated by acoustic phonon scattering, two transport regimes separated by the Bloch-Grüneisen (BG) temperature T BG = 2hk F c ph /k B can be identified. 19 Here, k F is the Fermi wave vector, c ph the sound velocity, and k B the Boltzmann constant (T BG ∼ 57 K √ n for the longitudinal acoustic phonon with the two-dimensional carrier density n measured in units of 10 12 cm −2 ).…”

Section: Introductionmentioning

confidence: 99%

Unraveling the acoustic electron-phonon interaction in graphene

2012

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Using a first-principles approach we calculate the electron-phonon couplings in graphene for the transverse and longitudinal acoustic phonons. Analytic forms of the coupling matrix elements valid in the long-wavelength limit are found to give an almost quantitative description of the first-principles matrix elements even at shorter wavelengths. Using the analytic forms of the coupling matrix elements, we study the acoustic phonon-limited carrier mobility and quasiparticle lifetime observable in photoemission spectroscopy for temperatures 0-200 K and high carrier densities of 10 12 -10 13 cm −2 . We find that the intrinsic effective acoustic deformation potential of graphene is eff = 6.8 eV and that the temperature dependence of the mobility μ ∼ T −α in the Bloch-Grüneisen regime increases beyond an α = 4 dependence even in the absence of screening when the true coupling matrix elements are considered. The α > 4 temperature dependence of the mobility is found to originate in a similar temperature dependence of the relaxation time at the Fermi level. The large disagreement between our calculated deformation potential and those extracted from experimental measurements (18-29 eV) indicates that additional or modified acoustic phonon-scattering mechanisms are at play in experimental situations.

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Section: Introductionmentioning

confidence: 99%

Unraveling the acoustic electron-phonon interaction in graphene

2012

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“…8,17 For charge transport, it has been shown that the carrier mobility of graphene devices on SiO 2 is mainly limited by interfacial charged impurities, surface roughness, and phonons. [18][19][20] The demonstration of an order-of-magnitude improvement in the mobility of graphene encapsulated between atomically flat, charge trap free boron nitride crystals 21,22 has triggered the recent spin transport studies in encapsulated single layer and recently bilayer graphene-based spin valves, where a spin-relaxation length of up to~12 μm and~24 μm have been observed, respectively. 23,24 For the case of bilayer graphene, the initial experiments on SiO 2 revealed an inverse scaling between spin and momentum relaxation times, for example, the longest spinrelaxation times were observed in the lowest-mobility devices.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Electronic spin transport in dual-gated bilayer graphene

et al. 2016

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The elimination of extrinsic sources of spin relaxation is key to realizing the exceptional intrinsic spin transport performance of graphene. Toward this, we study charge and spin transport in bilayer graphene-based spin valve devices fabricated in a new device architecture that allows us to make a comparative study by separately investigating the roles of the substrate and polymer residues on spin relaxation. First, the comparison between spin valves fabricated on SiO 2 and BN substrates suggests that substrate-related charged impurities, phonons and roughness do not limit the spin transport in current devices. Next, the observation of a fivefold enhancement in the spin-relaxation time of the encapsulated device highlights the significance of polymer residues on spin relaxation. We observe a spin-relaxation length of~10 μm in the encapsulated bilayer, with a charge mobility of 24 000 cm 2 Vs − 1 . The carrier density dependence on the spin-relaxation time has two distinct regimes; no4 × 10 12 cm − 2 , where the spin-relaxation time decreases monotonically as the carrier concentration increases, and n ⩾ 4 × 10 12 cm − 2 , where the spin-relaxation time exhibits a sudden increase. The sudden increase in the spin-relaxation time with no corresponding signature in the charge transport suggests the presence of a magnetic resonance close to the charge neutrality point. We also demonstrate, for the first time, spin transport across bipolar p-n junctions in our dual-gated device architecture that fully integrates a sequence of encapsulated regions in its design. At low temperatures, strong suppression of the spin signal was observed while a transport gap was induced, which is interpreted as a novel manifestation of the impedance mismatch within the spin channel. INTRODUCTIONGraphene is considered to be a promising spin-channel material for future spintronics applications 1 because of its high-electronic mobility, 2 weak spin-orbit coupling 3,4 and a negligible hyperfine interaction. 5,6 The initial spin transport studies were mainly performed on single-layer 7-10 and bilayer exfoliated graphene, 9,11 and large-area graphene 12-15 deposited on conventional SiO 2 substrates. Although enhanced spin-relaxation times have been reported for bilayer graphene-based devices compared with those based on a single layer, the relatively low spin diffusion constants overall yield a lower spin-relaxation length of only 1-2 μm, 9,11 far below the theoretical predictions. 16 One approach suggested for achieving a longer distance spin communication is to increase the spin diffusion constants by fabricating higher mobility devices. 8,17 For charge transport, it has been shown that the carrier mobility of graphene devices on SiO 2 is mainly limited by interfacial charged impurities, surface roughness, and phonons. [18][19][20] The demonstration of an order-of-magnitude improvement in the mobility of graphene encapsulated between atomically flat, charge trap free boron nitride crystals 21,22 has triggered the recent spin transport studies...

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“…The results of our investigation on the mechanisms of MIT and other intrinsic characteristics, such as thickness-dependent screening abilities and fast relaxation of hole carriers at the valence band, provide useful information much needed for improving the performance of the FET devices based on MoS 2 monolayers and multilayers. Figure 1a,b illustrates our specially designed MIS-M capacitor device, fabricated by transferring 23,36 exfoliated flakes of MoS 2 and hexagonal boron nitride (BN) on a Si substrate coated with a SiO 2 thin layer (300 nm). Exfoliated natural crystals of monolayer or multilayer MoS 2 were first transferred onto a BN sheet, serving as an ultra-smooth and disorder-free gate dielectric 37 .…”

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confidence: 99%

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

et al. 2015

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The metal-insulator transition is one of the remarkable electrical properties of atomically thin molybdenum disulphide. Although the theory of electron-electron interactions has been used in modelling the metal-insulator transition in molybdenum disulphide, the underlying mechanism and detailed transition process still remain largely unexplored. Here we demonstrate that the vertical metal-insulator-semiconductor heterostructures built from atomically thin molybdenum disulphide are ideal capacitor structures for probing the electron states. The vertical configuration offers the added advantage of eliminating the influence of large impedance at the band tails and allows the observation of fully excited electron states near the surface of molybdenum disulphide over a wide excitation frequency and temperature range. By combining capacitance and transport measurements, we have observed a percolation-type metal-insulator transition, driven by density inhomogeneities of electron states, in monolayer and multilayer molybdenum disulphide. In addition, the valence band of thin molybdenum disulphide layers and their intrinsic properties are accessed.

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A transfer technique for high mobility graphene devices on commercially available hexagonal boron nitride

Cited by 357 publications

References 14 publications

Unraveling the acoustic electron-phonon interaction in graphene

Unraveling the acoustic electron-phonon interaction in graphene

Electronic spin transport in dual-gated bilayer graphene

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

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