Evidence of electric field-tunable tunneling probability in graphene and metal contact

Peng, Songang; Jin, Zhi; Zhang, Dayong; Shi, Jingyuan; Zhang, Yanhui; Yu, Guanghui

doi:10.1039/c7nr02502e

Nanoscale

2017

DOI: 10.1039/c7nr02502e

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Evidence of electric field-tunable tunneling probability in graphene and metal contact

Songang Peng

Zhi Jin

Dayong Zhang

et al.

Abstract: The metal-graphene contact resistance has been identified to be a key bottleneck for achieving high performance of graphene transistors. It is crucial to understand the electrical properties of graphene and the carrier transport mechanism under the contact metal. Here, we have developed a new method of characterizing the electrical properties of graphene under the metal contact. It was found that the electrical properties of graphene under the metal can be tuned via the back-gate voltage and display ambipolar … Show more

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Cited by 18 publications

(33 citation statements)

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“…Unfortunately, there have been few reports concentrating on this issue because of the difficulty to measure the electrical propriety of MoS 2 beneath the metal. Recently, we developed a modified transfer length method to realize the electrical property and carrier transport of 2D graphene film under the metal contact . Through this method, the sheet resistances of MoS 2 both under metal contact ( R SK ) and in channel ( R SH ) are obtained through our method.…”

mentioning

confidence: 99%

“…The current flowing into the metal from the MoS 2 sheet is highest near the contact edge x = 0 and drops nearly exponentially with the distance (seen in Figure a). The distance that the current drops to 1/ e of the total current is defined as transfer length L T . Based on the modified transmission line model that we developed, the potential distribution under the metal contact V ( x ) can be expressed as below

V (x) = \frac{I \sqrt{R_{SK} ρ_{C}}}{W} \frac{\cosh ([], false(L - x false) / L_{T})}{\sinh (L / L_{T})}

where L is the contact length, W is the contact width, ρ C is the specific contact resistivity, and I is the total current flowing into the contact region.…”

mentioning

confidence: 99%

“…Meanwhile, the voltage drop at the end of the contact, V ( x = L ), to the total current flowing into the contact, I ( x = 0) = I , is defined as the contact end resistance R CE . The R CE can be expressed as

R_{CE} = \frac{V (x = L)}{I (x = 0)} = \frac{\sqrt{R_{SK} ρ_{C}}}{W} \frac{1}{\sinh (L / L_{T})} = \frac{ρ_{C}}{W L_{T}} \frac{1}{\sinh (L / L_{T})}

…”

mentioning

confidence: 99%

See 2 more Smart Citations

Metal‐Contact‐Induced Transition of Electrical Transport in Monolayer MoS₂: From Thermally Activated to Variable‐Range Hopping

Peng

Jin

Yao

et al. 2019

Adv Elect Materials

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with semiconductor properties due to their bandgaps. Monolayer molybdenum disulfide (MoS 2 ), one of the TMDs, is found to have a direct bandgap of ≈1.8 eV, leading to low-power dissipation electronic devices, good carrier mobility (up to hundreds of cm 2 V −1 s −1 , a high current on/ off ratio (≈10 8 ), a steep subthreshold swing (74 mV decade −1 ), and atomically thin layered structure, suppressing short channel effects. [1][2][3][4][5][6][7][8][9] However, the metal-MoS 2 contact resistance is always to be several or ten thousands of Ω µm, which is more than 30 times larger than the Si-metal contact and even larger than the graphene-metal contact. [10][11][12][13][14][15][16][17][18][19][20][21][22] This high value of contact resistance will be one key factor to affect the MoS 2 based device performance to a great extent. Usually, the Fermi level pinning effect induced non-negligible Schottky barriers are considered to be responsible for the large contact resistance. [10,17] To reduce the contact resistance, ultrathin layers such as: graphene, Ta 2 O 5 , and hexagonal boron nitride (h-BN) are inserted at the MoS 2 /metal interface to attenuate the Fermi level pinning effect. [21][22][23][24][25] Benefiting from the lower Schottky barrier, the contact resistance of MoS 2 transistor can be reduced to 1.8 KΩ µm by introducing the inserting layer. [25] However, another kind of contact interface engineering method can further lower the contact resistance. For example, a chloride molecular treatment has been demonstrated to lower the contact resistance of MoS 2 transistor to 500 Ω µm. [26] On the other hand, formation of contacts to metallic-phase MoS 2 can reduce the contact resistance to 200-300 Ω µm. [27] Additionally, the clean graphene-MoS 2 interface with nickel-catalyzed etching graphene process can also reduce the contact resistance to 200 Ω µm. [28] These works suggest that other factors will affect the contact behavior of MoS 2 devices except the Fermi level pinning effect. Hence, understanding the intrinsic carrier transport of MoS 2 under metal contact is quite significant. Unfortunately, there have been few reports concentrating on this issue because of the difficulty to measure the electrical propriety of MoS 2 beneath the metal. Recently, we developed a modified transfer length method to realize the electrical property and carrier transport of 2D graphene film under the metal contact. [29][30][31] Through this method, the sheet resistances of MoS 2 both under metal contact (R SK ) and in channel (R SH ) are obtained through our An understanding of the charge transport of atomically thin molybdenum sulfide (MoS 2 ) beneath the metal electrode is important to the fabrication of high performance MoS 2 devices and circuits with low ohmic contact resistance. However, the carrier-transport mechanism in monolayer MoS 2 under the metal contact has remained elusive due to the difficulty of measuring the electrical properties of MoS 2 in contact regions. A method to distinguish the electrical properties of mon...

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mentioning

confidence: 99%

V (x) = \frac{I \sqrt{R_{SK} ρ_{C}}}{W} \frac{\cosh ([], false(L - x false) / L_{T})}{\sinh (L / L_{T})}

where L is the contact length, W is the contact width, ρ C is the specific contact resistivity, and I is the total current flowing into the contact region.…”

mentioning

confidence: 99%

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Metal‐Contact‐Induced Transition of Electrical Transport in Monolayer MoS₂: From Thermally Activated to Variable‐Range Hopping

Peng

Jin

Yao

et al. 2019

Adv Elect Materials

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“…[20,21] Through this method, the origin of the double Dirac point has been systematically studied. [20,21] Through this method, the origin of the double Dirac point has been systematically studied.…”

mentioning

confidence: 99%

“…The graphene channel width is 20 µm and the channel length varies from 3 to 11 µm, in steps of 2 µm. [20,21] Considering the contact end resistance, the sheet resistances under and outside the contact are extracted, respectively, and their values are quite different. The drain voltage (V DS ) is fixed at 0.5 V while the back gate voltage (V BG ) varies from −60 to 60 V. Color maps of I DS versus V BG and V DS for different channel length GFETs are shown in the Supporting Information.…”

mentioning

confidence: 99%

How Do Contact and Channel Contribute to the Dirac Points in Graphene Field‐Effect Transistors?

Peng

Jin

Zhang

et al. 2018

Adv Elect Materials

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electronics. [1][2][3][4][5] The cause of the amazing electronic properties of graphene is its unique line-up band structure, in which the valence and conduction bands meet in a single point at the Fermi level. This peculiar point is the so-called Dirac points and cones. [1] In graphene field-effect transistor (GFET), the channel conductance is modulated by the electric field from a back-or top-gate. The transfer characteristics, I DS -V GS curves typically display a V shape, with a hole-dominated conductance (p-branch) at lower V GS and electron type transport at more positive gate voltages (n-branch). The valley of the curves is the charge neutrality where the concentration of electron is equal to that of hole. This valley corresponds to the Dirac point in graphene band structure and quite important for electronic applications of graphene. For example, both the graphene frequency doubler and ambipolar mixer are biased at the Dirac point for their best performance. [6][7][8][9] In most case, only one unique Dirac point was found in the transfer characteristic of GFET. [10][11][12][13] Recently, several research groups found that the transfer characteristics in GFET show an additional minimum other than the major Dirac point, in other words, a doubledips curves. Nouchi and Tanigaki have found an anomalous distortion in GFET with ferromagnetic metal electrodes. [14] The transfer characteristics in these GFETs show two local minimal current points at hole branch. They attribute this phenomenon to the oxide layer induced weaker pinning of charge density at the metal contacts. Brenner and Murali have utilized hydrogen silsesquoxane film to partially cover the graphene channel, which leads to the different doping levels in channel region and a formation of p-n junction. An additional minimum conductance other than the Dirac point can also be observed in this GFET. [15] Chiu et al. found that an additional dip will appear on the left-hand side of the original Dirac point in I DS -V BG curve in the high field regime. They claim that this double dip structure can be attributed to the formation of a p-n junction in drain region, which is induced by the trapped charge doping under high bias conditions. [16] Bartolomeo et al. show that a double Dirac point can also been achieved while keeping the drain bias very low (20 mV). They have clarified that the double Dirac point is related to charge transfer between graphene and metal contact and that it is enhanced by the charge storage at The Dirac point(s) in graphene field-effect transistors (GFETs) are of great importance for electronic application. However, the lack of the effective means to distinguish the electrical properties of graphene at the contact and channel regions limits a clear understanding of their contributions to the Dirac point(s). A method, which can characterize the electrical properties of graphene under metal contact and in the channel, is developed, respectively. It is found that the Fermi levels of graphene at the contact and channel regions are quite ...

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The Effect of Metal Contact Doping on the Scaled Graphene Field Effect Transistor

et al. 2021

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Evidence of electric field-tunable tunneling probability in graphene and metal contact

Cited by 18 publications

References 45 publications

Metal‐Contact‐Induced Transition of Electrical Transport in Monolayer MoS₂: From Thermally Activated to Variable‐Range Hopping

Metal‐Contact‐Induced Transition of Electrical Transport in Monolayer MoS₂: From Thermally Activated to Variable‐Range Hopping

How Do Contact and Channel Contribute to the Dirac Points in Graphene Field‐Effect Transistors?

The Effect of Metal Contact Doping on the Scaled Graphene Field Effect Transistor

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Evidence of electric field-tunable tunneling probability in graphene and metal contact

Cited by 18 publications

References 45 publications

Metal‐Contact‐Induced Transition of Electrical Transport in Monolayer MoS2: From Thermally Activated to Variable‐Range Hopping

Metal‐Contact‐Induced Transition of Electrical Transport in Monolayer MoS2: From Thermally Activated to Variable‐Range Hopping

How Do Contact and Channel Contribute to the Dirac Points in Graphene Field‐Effect Transistors?

The Effect of Metal Contact Doping on the Scaled Graphene Field Effect Transistor

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Product

Resources

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Metal‐Contact‐Induced Transition of Electrical Transport in Monolayer MoS₂: From Thermally Activated to Variable‐Range Hopping

Metal‐Contact‐Induced Transition of Electrical Transport in Monolayer MoS₂: From Thermally Activated to Variable‐Range Hopping