Mobility of Charge Carriers in Semiconducting Layer Structures

Fivaz, Roland; Mooser, E.

doi:10.1103/physrev.163.743

Cited by 570 publications

(385 citation statements)

References 15 publications

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“…Variable temperature electrical measurements performed on WSe 2 FETs with low-resistance graphene contacts reveal that as the temperature decreases from 160 to 77 K, the extrinsic field-effect mobility increases from ∼196 to ∼330 cm 2 V −1 s −1 for the electron channel and from ∼204 to ∼270 cm 2 V −1 s −1 for the hole channel. These mobility values are comparable to the highest electron and hole mobilities reported on thin film WSe 2 FETs as well as bulk WSe 2 , 8,10,12,34 indicating that our graphene-contacted few-layer WSe 2 devices approach the intrinsic phonon-limited mobility for both electrons and holes. The most significant finding of our study is that highly "doped" graphene is an excellent contact electrode material for high-performance p-and n-type TMD FETs.…”

supporting

confidence: 80%

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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supporting

confidence: 80%

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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“…It is expected that MoS 2 devices with mobilities limited by homopolar, optical phonons should follow this form in this temperature range, with g = 1.69 for monolayer 35 and g = 2.6 for bulk MoS 2 . 36 The monolayer value agrees well with the prediction, though we note that the fit was obtained over a limited temperature range.…”

supporting

confidence: 74%

“…35 At lower temperatures, scattering from phonons should be dominated by acoustic modes with a linear dependence of mobility on temperature, 36 in contrast with the near saturation we observe (Fig. 3c,d).…”

contrasting

confidence: 49%

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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“…Some of the first electrical measurements on semiconducting TMDs date back to the 1960s, when Fivaz and Moser showed that the carrier mobility of MoS 2 , MoSe 2 , and WSe 2 exceed 100 cm 2 /(V s) in the direction along the layers. 5 In 2004, the first transistors were fabricated on the surface of bulk WSe 2 crystals, 6 showing high mobility and ambipolar behavior. The room-temperature on/off ratio was however rather low (∼10) because of bulk conduction.…”

Section: ■ Introductionmentioning

confidence: 99%

Single-Layer MoS₂ Electronics

2015

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CONSPECTUS: Atomic crystals of two-dimensional materials consisting of single sheets extracted from layered materials are gaining increasing attention. The most well-known material from this group is graphene, a single layer of graphite that can be extracted from the bulk material or grown on a suitable substrate. Its discovery has given rise to intense research effort culminating in the 2010 Nobel Prize in physics awarded to Andre Geim and Konstantin Novoselov. Graphene however represents only the proverbial tip of the iceberg, and increasing attention of researchers is now turning towards the veritable zoo of so-called "other 2D materials". They have properties complementary to graphene, which in its pristine form lacks a bandgap: MoS 2 , for example, is a semiconductor, while NbSe 2 is a superconductor. They could hold the key to important practical applications and new scientific discoveries in the two-dimensional limit. This family of materials has been studied since the 1960s, but most of the research focused on their tribological applications: MoS 2 is best known today as a high-performance dry lubricant for ultrahigh-vacuum applications and in car engines. The realization that single layers of MoS 2 and related materials could also be used in functional electronic devices where they could offer advantages compared with silicon or graphene created a renewed interest in these materials. MoS 2 is currently gaining the most attention because the material is easily available in the form of a mineral, molybdenite, but other 2D transition metal dichalcogenide (TMD) semiconductors are expected to have qualitatively similar properties. In this Account, we describe recent progress in the area of single-layer MoS 2 -based devices for electronic circuits. We will start with MoS 2 transistors, which showed for the first time that devices based on MoS 2 and related TMDs could have electrical properties on the same level as other, more established semiconducting materials. This allowed rapid progress in this area and was followed by demonstrations of basic digital circuits and transistors operating in the technologically relevant gigahertz range of frequencies, showing that the mobility of MoS 2 and TMD materials is sufficiently high to allow device operation at such high frequencies. Monolayer MoS 2 and other TMDs are also direct band gap semiconductors making them interesting for realizing optoelectronic devices. These range from simple phototransistors showing high sensitivity and low noise, to light emitting diodes and solar cells. All the electronic and optoelectronic properties of MoS 2 and TMDs are accompanied by interesting mechanical properties with monolayer MoS 2 being as stiff as steel and 30× stronger. This makes it especially interesting in the context of flexible electronics where it could combine the high degree of mechanical flexibility commonly associated with organic semiconductors with high levels of electrical performance. All these results show that MoS 2 and TMDs are promising materials for elect...

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Mobility of Charge Carriers in Semiconducting Layer Structures

Cited by 570 publications

References 15 publications

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

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

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

Single-Layer MoS₂ Electronics

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Mobility of Charge Carriers in Semiconducting Layer Structures

Cited by 570 publications

References 15 publications

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

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

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

Single-Layer MoS2 Electronics

Contact Info

Product

Resources

About

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

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

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

Single-Layer MoS₂ Electronics