Mobility enhancement and highly efficient gating of monolayer MoS<sub>2</sub> transistors with polymer electrolyte

Lin, Ming; Liu, Lezhang; Lan, Qing; Tan, Xuebin; Dhindsa, Kulwinder; Zeng, Peng; Naik, V. M.; Cheng, Mark Ming Cheng; Zhou, Zhixian

doi:10.1088/0022-3727/45/34/345102

Cited by 143 publications

(111 citation statements)

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“…Encapsulating MoS 2 in a high-k dielectric has shown substantial mobility improvements. 10,14,[23][24][25][26] The devices reported here are not in a high-k environment, however, suggesting the possibility of further mobility improvement in future devices.…”

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confidence: 84%

Intrinsic Electronic Transport Properties of High-Quality Monolayer and Bilayer MoS₂

et al. 2013

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We report electronic transport measurements of devices based on monolayers and bilayers of the transition-metal dichalcogenide MoS 2 . Through a combination of in situ vacuum annealing and electrostatic gating we obtained ohmic contact to the MoS 2 down to 4 K at high carrier densities. At lower carrier densities, low temperature four probe transport measurements show a metal-insulator transition in both monolayer and bilayer samples. In the metallic regime, the high temperature behavior of the mobility showed strong temperature dependence consistent with phonon dominated transport. At low temperature, intrinsic field-effect mobilities greater than 1000 cm 2 /Vs were observed for both monolayer and bilayer devices. Mobilities extracted from Hall effect measurements were several times lower and showed a strong dependence on density, likely caused by screening of charged impurity scattering at higher densities.

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confidence: 84%

Intrinsic Electronic Transport Properties of High-Quality Monolayer and Bilayer MoS₂

et al. 2013

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“…In particular, single-layer MoS 2 (SLM) has been the focus of much research [3][4][5][6][7][8]. Like single-layer graphene (SLG), SLM is an atomically thin two-dimensional crystal.…”

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confidence: 99%

Mobility enhancement and temperature dependence in top-gated single-layer MoS2

2013

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The deposition of a high-κ oxide overlayer is known to significantly enhance the room-temperature electron mobility in single-layer MoS2 (SLM) but not in single-layer graphene (SLG). We give a quantitative account of how this mobility enhancement is due to the non-degeneracy of the twodimensional electron gas system in SLM at accessible temperatures. Using our charged impurity scattering model [Ong and Fischetti, Phys. Rev. B 86, 121409 (2012)] and temperature-dependent polarizability, we calculate the charged impurity-limited mobility (µimp) in SLM with and without a high-κ (HfO2) top gate oxide at different electron densities and temperatures. We find that the mobility enhancement is larger at low electron densities and high temperatures because of finite-temperature screening, thus explaining the enhancement of the mobility observed at room temperature. µimp is shown to decrease significantly with increasing temperature, suggesting that the strong temperature dependence of measured mobilities should not be interpreted as being solely due to inelastic scattering with phonons. We also reproduce the recently seen experimental trend in which the temperature scaling exponent (γ) of µimp ∝ T −γ is smaller in top-gated SLM than in bare SLM. Finally, we show that a ∼ 37 percent mobility enhancement can be achieved by reducing the HfO2 thickness from 20 to 2 nm.

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“…21 Measuring the electrical property of IL-gated devices below the freezing point of the IL also eliminates possible coupling between the Si back and IL gate. 21,37 We have measured several WSe 2 devices with IL-gated graphene drain and source contacts. Among these, two devices had h-BN channel passivation, one had its channel covered by a 50 nm thick Al 2 O 3 layer, and a few other devices had bare channels (uncovered).…”

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High Mobility WSe₂ p- and n-Type Field-Effect Transistors Contacted by Highly Doped Graphene for Low-Resistance Contacts

et al. 2014

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ABSTRACT:We report the fabrication of both n-type and p-type WSe 2 fieldeffect transistors with hexagonal boron nitride passivated channels and ionic-liquid (IL)-gated graphene contacts. Our transport measurements reveal intrinsic channel properties including a metal−insulator transition at a characteristic conductivity close to the quantum conductance e 2 /h, a high ON/OFF ratio of >10 7 at 170 K, and large electron and hole mobility of μ ≈ 200 cm 2 V −1 s −1 at 160 K. Decreasing the temperature to 77 K increases mobility of electrons to ∼330 cm 2 V −1 s −1 and that of holes to ∼270 cm 2 V −1 s −1 . We attribute our ability to observe the intrinsic, phonon-limited conduction in both the electron and hole channels to the drastic reduction of the Schottky barriers between the channel and the graphene contact electrodes using IL gating. We elucidate this process by studying a Schottky diode consisting of a single graphene/WSe 2 Schottky junction. Our results indicate the possibility to utilize chemically or electrostatically highly doped graphene for versatile, flexible, and transparent low-resistance ohmic contacts to a wide range of quasi-2D semiconductors. KEYWORDS: MoS 2 , WSe 2 , field-effect transistor, graphene, Schottky barrier, ionic-liquid gate L ayered transition metal dichalcogenides (TMDs) have recently emerged as promising materials for flexible electronics and optoelectronics applications. These systems have demonstrated many "graphene-like" properties including a relatively high carrier mobility, mechanical flexibility, chemical and thermal stability, and moreover offer the significant advantage of a substantial band gap. 1 Field-effect transistors (FETs) with atomically thin TMD channels are immune to short channel effects. 2 In addition, pristine surfaces of twodimensional (2D) TMDs are free of dangling bonds, which reduce surface roughness scattering and interface traps. Atomic layers of MoS 2 are probably the most extensively studied among the layered TMDs due to the availability of large natural molybdenite crystals from mining sources. 3 In addition to MoS 2 , several other semiconducting TMDs such as MoSe 2 , WS 2 , and WSe 2 with different band structures and charge neutrality levels may offer additional distinct properties. 1,4 However, the number of studies on TMDs other than MoS 2 is still small. 5−14 Among these studies, back-gated WSe 2 monolayer FETs with surface doping have already demonstrated a high field-effect mobility 8 reaching ∼140 cm 2 V −1 s −1 , which is substantially higher than most of the reported roomtemperature mobility values for MoS 2 . 15−19 A high intrinsic hole mobility of up to 500 cm 2 V −1 s −1 was also observed in bulk WSe 2 FETs. 11 Furthermore, WSe 2 is more resistant to oxidation in humid environments than MoS 2 . 10,20 A major challenge for developing WSe 2 -based electronic devices is that WSe 2 tends to form a substantial Schottky barrier (SB) with most metals commonly used for making electrical contacts. 8,13 This is a strong disadvantage, because lowre...

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Mobility enhancement and highly efficient gating of monolayer MoS₂ transistors with polymer electrolyte

Cited by 143 publications

References 28 publications

Intrinsic Electronic Transport Properties of High-Quality Monolayer and Bilayer MoS₂

Intrinsic Electronic Transport Properties of High-Quality Monolayer and Bilayer MoS₂

Mobility enhancement and temperature dependence in top-gated single-layer MoS2

High Mobility WSe₂ p- and n-Type Field-Effect Transistors Contacted by Highly Doped Graphene for Low-Resistance Contacts

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Mobility enhancement and highly efficient gating of monolayer MoS2 transistors with polymer electrolyte

Cited by 143 publications

References 28 publications

Intrinsic Electronic Transport Properties of High-Quality Monolayer and Bilayer MoS2

Intrinsic Electronic Transport Properties of High-Quality Monolayer and Bilayer MoS2

Mobility enhancement and temperature dependence in top-gated single-layer MoS2

High Mobility WSe2 p- and n-Type Field-Effect Transistors Contacted by Highly Doped Graphene for Low-Resistance Contacts

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Product

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Mobility enhancement and highly efficient gating of monolayer MoS₂ transistors with polymer electrolyte

Intrinsic Electronic Transport Properties of High-Quality Monolayer and Bilayer MoS₂

Intrinsic Electronic Transport Properties of High-Quality Monolayer and Bilayer MoS₂

High Mobility WSe₂ p- and n-Type Field-Effect Transistors Contacted by Highly Doped Graphene for Low-Resistance Contacts