High-quality electrical transport using scalable CVD graphene (original) (raw)
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Low-temperature quantum transport in CVD-grown single crystal graphene
Nano Research, 2016
Chemical vapor deposition (CVD) has been proposed for large-scale graphene synthesis for practical applications. However, the inferior electronic properties of CVD graphene are one of the key problems to be solved. In this study, we present a detailed study on the electronic properties of high-quality single crystal monolayer graphene. The graphene is grown by CVD on copper using a cold-wall reactor and then transferred to Si/SiO2. Our low-temperature magneto-transport data demonstrate that the characteristics of the measured single-crystal CVD graphene samples are superior to those of polycrystalline graphene and have a quality which is comparable to that of exfoliated graphene on Si/SiO2. The Dirac point in our best samples is located at back-gate voltages of less than 10V, and their mobility can reach 11000 cm 2 /Vs. More than 12 flat and discernible half-integer quantum Hall plateaus have been observed in high magnetic field on both the electron and hole side of the Dirac point. At low magnetic field, the magnetoresistance shows a clear weak localization peak. Using the theory of McCann et al., we find that the inelastic scattering length is larger than 1 μm in these samples even at the charge neutrality point.
Exploring carrier transport phenomena in a CVD-assembled graphene FET on hexagonal boron nitride
Nanotechnology, 2012
The supporting substrate plays a crucial role in preserving the superb electrical characteristics of an atomically thin 2D carbon system. We explore carrier transport behavior in a chemical-vapor-deposition- (CVD-) assembled graphene monolayer on hexagonal boron nitride (h-BN) substrate. Graphene-channel field-effect transistors (GFETs) were fabricated on ultra-thin h-BN multilayers to screen out carrier scattering from the underlying SiO2 substrate. To explore the transport phenomena, we use three different approaches to extract carrier mobility, namely, effective carrier mobility (μeff), intrinsic carrier mobility (μ), and field-effect mobility (μFE). A comparative study has been conducted based on the electrical characterization results, uncovering the impacts of supporting substrate material and device geometry scaling on carrier mobility in GFETs with CVD-assembled graphene as the active channel.
Applied Physics Letters, 2010
We report on electronic properties of graphene synthesized by chemical vapor deposition ͑CVD͒ on copper then transferred to SiO 2 / Si. Wafer-scale ͑up to 4 in.͒ graphene films have been synthesized, consisting dominantly of monolayer graphene as indicated by spectroscopic Raman mapping. Low temperature transport measurements are performed on microdevices fabricated from such CVD graphene, displaying ambipolar field effect ͑with on/off ratio ϳ5 and carrier mobilities up to ϳ3000 cm 2 / V s͒ and "half-integer" quantum Hall effect, a hall-mark of intrinsic electronic properties of monolayer graphene. We also observe weak localization and extract information about phase coherence and scattering of carriers.
Magneto-transport of large CVD-grown graphene
2010
We present magnetoresistance measurements on large scale monolayer graphene grown by chemical vapor deposition (CVD) on copper. The graphene layer was transferred onto SiO2/Si via PMMA and thermal release tape for transport measurements. The resulting centimeter-sized graphene samples were measured at temperatures down to 30mK in a magnetic field. We observe a very sharp peak in resistance at zero field, which is well fitted by weak localization theory as well as strong localization. The samples exhibit conductance fluctuations symmetric in field, which are due to large scale inhomogeneities consistent with the grain boundaries of copper during the CVD growth.
High-Mobility, Wet-Transferred Graphene Grown by Chemical Vapor Deposition
ACS Nano, 2019
We report high room-temperature mobility in single layer graphene grown by Chemical Vapor Deposition (CVD) after wet transfer on SiO2 and hexagonal boron nitride (hBN) encapsulation. By removing contaminations trapped at the interfaces between single-crystal graphene and hBN, we achieve mobilities up to∼ 70000cm 2 V −1 s −1 at room temperature and∼ 120000cm 2 V −1 s −1 at 9K. These are over twice those of previous wet transferred graphene and comparable to samples prepared by dry transfer. We also investigate the combined approach of thermal annealing and encapsulation in polycrystalline graphene, achieving room temperature mobilities∼ 30000cm 2 V −1 s −1. These results show that, with appropriate encapsulation and cleaning, room temperature mobilities well above 10000cm 2 V −1 s −1 can be obtained in samples grown by CVD and transferred using a conventional, easily scalable PMMA-based wet approach.
Transport behaviors of graphene 2D field-effect transistors on boron nitride substrate
2012 13th International Conference on Ultimate Integration on Silicon (ULIS), 2012
We model the transport behavior of a top-gated graphene field-effect transistor where boron nitride is used as substrate and gate insulator material. Our simulation model is based on the non-equilibrium Green's function approach to solving a tight-binding Hamiltonian for graphene, selfconsistently coupled with Poisson's equation. The analysis emphasizes the effects of the chiral character of carriers in graphene in the different transport regimes including Klein and band-to-band tunneling processes. We predict the possible emergence of negative differential conductance and investigate its dependence on the temperature and the BN-induced bandgap. Short-channel effects are evaluated from the analysis of transfer characteristics as a function of gate length and gate insulator thickness. They manifest through the shift of the Dirac point and the appearance of current oscillations at short gate length.
Upscaling high-quality CVD graphene devices to 100 micron-scale and beyond
Applied Physics Letters, 2017
We describe a method for transferring ultra large-scale CVD-grown graphene sheets. These samples can be fabricated as large as several cm 2 and are characterized by magneto-transport measurements on SiO 2 substrates. The process we have developed is highly effective and limits damage to the graphene all the way through metal liftoff, as shown in carrier mobility measurements and the observation of the quantum Hall effect. The charge-neutral point is shown to move drastically to near-zero gate voltage after a 2-step post-fabrication annealing process, which also allows for greatly diminished hysteresis.
Vertical transport in graphene- hexagonal boron nitride heterostructure devices OPEN
Research in graphene-based electronics is recently focusing on devices based on vertical heterostructures of two-dimensional materials. Here we use density functional theory and multiscale simulations to investigate the tunneling properties of single-and double-barrier structures with graphene and few-layer hexagonal boron nitride (h-BN) or hexagonal boron carbon nitride (h-BC 2 N). We find that tunneling through a single barrier exhibit a weak dependence on energy. We also show that in double barriers separated by a graphene layer we do not observe resonant tunneling, but a significant increase of the tunneling probability with respect to a single barrier of thickness equal to the sum of the two barriers. This is due to the fact that the graphene layer acts as an effective phase randomizer, suppressing resonant tunneling and effectively letting a double-barrier structure behave as two single-barriers in series. Finally, we use multiscale simulations to reproduce a current-voltage characteristics resembling that of a resonant tunneling diode, that has been experimentally observed in single barrier structure. The peak current is obtained when there is perfect matching between the densities of states of the cathode and anode graphene regions. Vertical heterostructures of two-dimensional materials are the subject of intense investigation for the possibility they offer to engineer and taylor specific electrical and optical characteristics 1. In graphene-based electronics, transistors based on vertical heterostructures are studied because they can achieve large current modulation, if large bandgap layers are included that can effectively block current in the off state. Therefore, a few transistor concepts based on vertical transport have been proposed 2,3 and experimentally demonstrated 4–6 in recent years. Vertical heterostructures of two-dimensional materials are qualitatively different from the well known heterostructures based on the III-V and II-VI materials systems. Indeed, adjacent layers can have very different Hamiltonians and transverse energy-dispersion relations. This aspect can lead to the emergence of peculiar transport properties. The choice of the materials stacked with graphene is crucial, since the deposition and growth of graphene on a dielectric substrate can significantly alter its electronic properties and suppress 7,8 the extremely high mobility observed in suspendend samples 9–12. Hexagonal boron nitride (h-BN) is considered a promising dielectric 13–16 , having a honeycomb lattice closely matching that of graphene 17 , and only weakly interacting with deposited monolayer 14,18 or bilayer graphene 19. In this paper, we report some peculiar properties of vertical transport through single-and double-barrier heterostructures of graphene and h-BN or h-BC 2 N layers, that we have studied by means of density functional theory. In detail, we will show that tunneling through a single insulating barrier has a small dependence on energy in a large portion of the bandgap (Section II), and that a graphene layer between two tunneling