Mobility enhancement and temperature dependence in top-gated single-layer MoS_{2} (original) (raw)
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Band-like transport in high mobility unencapsulated single-layer MoS2 transistors
Applied Physics Letters, 2013
Ultra-thin MoS 2 has recently emerged as a promising two-dimensional semiconductor for electronic and optoelectronic applications. Here, we report high mobility (>60 cm 2 /Vs at room temperature) field-effect transistors that employ unencapsulated single-layer MoS 2 on oxidized Si wafers with a low level of extrinsic contamination. While charge transport in the sub-threshold regime is consistent with a variable range hopping model, monotonically decreasing field-effect mobility with increasing temperature suggests band-like transport in the linear regime. At temperatures below 100 K, temperature-independent mobility is limited by Coulomb scattering, whereas, at temperatures above 100 K, phonon-limited mobility decreases as a power law with increasing temperature. V C 2013 AIP Publishing LLC. [http://dx.
Giant Intrinsic Carrier Mobilities in Graphene and Its Bilayer
Physical Review Letters, 2008
We have studied temperature dependences of electron transport in graphene and its bilayer and found extremely low electron-phonon scattering rates that set the fundamental limit on possible charge carrier mobilities at room temperature. Our measurements show that mobilities higher than 200,000 cm 2 /Vs are achievable, if extrinsic disorder is eliminated. A sharp (threshold-like) increase in resistivity observed above ∼200K is unexpected but can qualitatively be understood within a model of a rippled graphene sheet in which scattering occurs on intraripple flexural phonons. Graphene exhibits remarkably high electronic quality such that charge carriers in this one-atom-thick material can travel ballistically over submicron distances [1]. Electronic quality of materials is usually characterized by mobility μ of their charge carriers, and values of μ as high as 20,000 cm 2 /Vs were reported for single-layer graphene (SLG) at low temperatures (T) [2-5]. It is also believed that μ in the existing samples is limited by
Thickness-dependent electron mobility of single and few-layer MoS2 thin-film transistors
AIP Advances
We investigated the dependence of electron mobility on the thickness of MoS 2 nanosheets by fabricating bottom-gate single and few-layer MoS 2 thin-film transistors with SiO 2 gate dielectrics and Au electrodes. All the fabricated MoS 2 transistors showed on/off-current ratio of ∼10 7 and saturated output characteristics without high-k capping layers. As the MoS 2 thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS 2 transistors increased from ∼10 to ∼18 cm 2 V −1 s −1. The increased subthreshold swing of the fabricated transistors with MoS 2 thickness suggests that the increase of MoS 2 mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS 2 layer on its thickness.
Multi-terminal transport measurements of MoS2 using a van der Waals heterostructure device platform
Nature Nanotechnology, 2015
Atomically thin two-dimensional semiconductors such as MoS 2 hold great promise for electrical, optical and mechanical devices and display novel physical phenomena. However, the electron mobility of mono-and few-layer MoS 2 has so far been substantially below theoretically predicted limits, which has hampered efforts to observe its intrinsic quantum transport behaviours. Potential sources of disorder and scattering include defects such as sulphur vacancies in the MoS 2 itself as well as extrinsic sources such as charged impurities and remote optical phonons from oxide dielectrics. To reduce extrinsic scattering, we have developed here a van der Waals heterostructure device platform where MoS 2 layers are fully encapsulated within hexagonal boron nitride and electrically contacted in a multi-terminal geometry using gate-tunable graphene electrodes. Magneto-transport measurements show dramatic improvements in performance, including a recordhigh Hall mobility reaching 34,000 cm 2 V -1 s -1 for six-layer MoS 2 at low temperature, confirming that low-temperature performance in previous studies was limited by extrinsic interfacial impurities rather than bulk defects in the MoS 2 . We also observed Shubnikov-de Haas oscillations in high-mobility monolayer and few-layer MoS 2 . Modelling of potential scattering sources and quantum lifetime analysis indicate that a combination of short-range and long-range interfacial scattering limits the low-temperature mobility of MoS 2 .
Effective mobility of single-layer graphene transistors as a function of channel dimensions
Journal of Applied Physics, 2011
A detailed analysis of the extracted back gated FET mobility as a function of channel length, channel width, and underlying oxide thickness for both exfoliated and chemical vapor deposited (CVD) graphene is presented. The mobility increases with increasing channel length eventually saturating at a constant value for channel lengths of several micrometers. The length dependence is consistent with the transition from a ballistic to diffusive transport regime. The mobility as a function of channel width first increases and then decreases. The increase in mobility for very small channel widths is consistent with a reduction in edge scattering. The decrease in mobility for larger channel widths is observed to be strongly dependent on the oxide thickness suggesting that electrostatics associated with fringing fields is an important effect. This effect is further confirmed by a comparative analysis of the measured mobility of graphene devices with similar channel dimensions on oxides of di...
Thermal transport in MoS2/Graphene hybrid nanosheets
Heat dissipation is a very critical problem for designing nano-functional devices, including MoS2/graphene heterojunctions. In this paper we investigate thermal transport in MoS2/graphene hybrid nanosheets under various heating conditions, by using molecular dynamics simulation. Diverse transport processes and characteristics, depending on the conducting layers, are found in these structures. The thermal conductivities can be tuned by interlayer coupling, environment temperature, and interlayer overlap. The highest thermal conductivity at room temperature is achieved as more than 5 times of that of single-layer MoS2 when both layers are heated and 100% overlapped. Different transport mechanisms in the hybrid nanosheets are explained by phonon density of states, temperature distribution, and interlayer thermal resistance. Our results could not only provide clues to master the heat transport in functional devices based on MoS2/graphene heterojunctions, but are also useful for analyzing thermal transport in other van der Waals hybrid nanosheets.
Strain induced mobility modulation in single-layer MoS2
Journal of Physics D: Applied Physics, 2015
In this paper the effect of biaxial and uniaxial strain on the mobility of single-layer MoS 2 for temperatures T > 100 K is investigated. Scattering from intrinsic phonon modes, remote phonon and charged impurities are considered along with static screening. Ab-initio simulations are utilized to investigate the strain induced effects on the electronic bandstructure and the linearized Boltzmann transport equation is used to evaluate the low-field mobility under various strain conditions. The results indicate that the mobility increases with tensile biaxial and tensile uniaxial strain along the armchair direction. Under compressive strain, however, the mobility exhibits a non-monotonic behavior when the strain magnitude is varied. In particular, with a relatively small compressive strain of 1% the mobility is reduced by about a factor of two compared to the unstrained condition, but with a larger compressive strain the mobility partly recovers such a degradation.
Tuning transport across MoS2/graphene interfaces via as-grown lateral heterostructures
npj 2D Materials and Applications, 2020
An unexploited property of graphene-based heterojunctions is the tunable doping of the junction via electrostatic gating. This unique property may be key in advancing electronic transport across interfaces with semiconductors. Here, we engineer transport in semiconducting TMDs by constructing a lateral heterostructure with epitaxial graphene and tuning its intrinsic doping to form a p–n junction between the graphene and the semiconducting TMDs. Graphene grown on SiC (epitaxial graphene) is intrinsically doped via substrate polarization without the introduction of an external dopant, thus enabling a platform for pristine heterostructures with a target band alignment. We demonstrate an electrostatically tunable graphene/MoS2p–n junction with >20× reduction and >10× increased tunability in contact resistance (Rc) compared with metal/TMD junctions, attributed to band alignment engineering and the tunable density of states in graphene. This unique concept provides improved control ...
Mobility in graphene double gate field effect transistors
Solid-State Electronics, 2008
In this work, double-gated field effect transistors manufactured from monolayer graphene are investigated. Conventional top-down CMOS-compatible processes are applied except for graphene deposition by manual exfoliation. Carrier mobilities in single-and doublegated graphene field effect transistors are compared. Even in double-gated graphene FETs, the carrier mobility exceeds the universal mobility of silicon over nearly the entire measured range. At comparable dimensions, reported mobilities for ultra thin body siliconon-insulator MOSFETs can not compete with graphene FET values.
ACS Nano, 2021
We demonstrate a graphene−MoS 2 architecture integrating multiple field-effect transistors (FETs), and we independently probe and correlate the conducting properties of van der Waals coupled graphene−MoS 2 contacts with those of the MoS 2 channels. Devices are fabricated starting from high-quality single-crystal monolayers grown by chemical vapor deposition. The heterojunction was investigated by scanning Raman and photoluminescence spectroscopies. Moreover, transconductance curves of MoS 2 are compared with the current−voltage characteristics of graphene contact stripes, revealing a significant suppression of transport on the n-side of the transconductance curve. On the basis of ab initio modeling, the effect is understood in terms of trapping by sulfur vacancies, which counterintuitively depends on the field effect, even though the graphene contact layer is positioned between the backgate and the MoS 2 channel.