A physics-based model of gate-tunable metal–graphene contact resistance benchmarked against experimental data

Chaves, Ferney A.; Jiménez, David; Sagade, Abhay A.; Kim, Wonjae; Riikonen, Juha; Lipsanen, Harri

doi:10.1088/2053-1583/2/2/025006

Cited by 37 publications

(44 citation statements)

References 26 publications

(47 reference statements)

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“…For different metals, we compare results of our simulations for the medium (point A) and short (point B) structures, with experimental and theoretical results from the literature. Material Medium structure Short structure Experimental Results Theoretical results (Ω · μ m) (Ω · μ m) reported (Ω · μ m) reported (Ω · μ m) Cu 1153 374 184–263 43 627 18 92–254 46 44 19 Ni 360 120 294 12 , 300 37 600 23 800 38 150–350 40 Pd 2899 2076 320–715 9 403 18 600 37 185–230 17 584 43 , 122–484 46 Pt 209 123 — 764 18 …”

Section: Resultsmentioning

confidence: 99%

Electrical properties of graphene-metal contacts

Cusati

Fiori

Gahoi

et al. 2017

Sci Rep

137

109

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The performance of devices and systems based on two-dimensional material systems depends critically on the quality of the contacts between 2D material and metal. A low contact resistance is an imperative requirement to consider graphene as a candidate material for electronic and optoelectronic devices. Unfortunately, measurements of contact resistance in the literature do not provide a consistent picture, due to limitations of current graphene technology, and to incomplete understanding of influencing factors. Here we show that the contact resistance is intrinsically dependent on graphene sheet resistance and on the chemistry of the graphene-metal interface. We present a physical model of the contacts based on ab-initio simulations and extensive experiments carried out on a large variety of samples with different graphene-metal contacts. Our model explains the spread in experimental results as due to uncontrolled graphene doping and suggests ways to engineer contact resistance. We also predict an achievable contact resistance of 30 Ω·μm for nickel electrodes, extremely promising for applications.

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Section: Resultsmentioning

confidence: 99%

Electrical properties of graphene-metal contacts

Cusati

Fiori

Gahoi

et al. 2017

Sci Rep

137

109

View full text Add to dashboard Cite

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“…When a metal is brought into contact with graphene, a junction with high contact resistivity is created, typically attributed to the low density of states (DOS) in graphene in particular when the Fermi level is near the Dirac point . Although ab initio calculations provide deeper insights into the contact problem, they also highlight the importance of the metal . Experimentally, various methods have been reported to reduce R C : one of the most common approaches is postmetallization annealing .…”

Section: Introductionmentioning

confidence: 99%

Ultralow Specific Contact Resistivity in Metal–Graphene Junctions via Contact Engineering

Passi

Gahoi

Marín

et al. 2018

Adv Materials Inter

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A systematic investigation of graphene edge contacts is provided. Intentionally patterning monolayer graphene at the contact region creates well-defined edge contacts that lead to a 67% enhancement in current injection from a gold contact. Specific contact resistivity is reduced from 1372 Ωµm for a device with surface contacts to 456 Ωµm when contacts are patterned with holes. Electrostatic doping of the graphene further reduces contact resistivity from 519 Ωµm to 45 Ωµm, a substantial decrease of 91%. The experimental results are supported and understood via a multi-scale numerical model, based on density-functional-theory calculations and transport simulations. The data is analyzed with regards to the edge perimeter and hole-to-graphene ratio, which provides insights into optimized contact geometries. The current work thus indicates a reliable and reproducible approach for fabricating low resistance contacts in graphene devices.We provide a simple guideline for contact design that can be exploited to guide graphene and 2D material contact engineering.The extraordinary electronic, optoelectronic and mechanical properties of graphene make it a promising candidate as a technology booster for micro-and nanoelectronics applications.Examples include radio frequency electronics, 1,2 integrated photodetectors, 3-5 and nanoelectromechanical systems. 6,7 One of the major bottlenecks limiting the performance of graphene-based devices is the large and varying value of specific contact resistivity (R C ) between metal contact electrodes and graphene. [8][9][10][11] When a metal is brought into contact with graphene, a junction with high contact resistivity is created, typically attributed to the low density of states (DOS) in graphene in particular when the Fermi level is near the Dirac point. 11 Although abinitio calculations provide deeper insights into the contact problem, they also highlight the importance of the metal. 12-14 Experimentally, various methods have been reported to reduce R C : one of the most common approaches is post-metallization annealing. [15][16][17] Other methods aim to modify the graphene prior to metallization in a random manner, such as low power oxygen plasma etch (with or without post-metallization annealing), 18 ozone pre-treatment, 19 intentional doping of graphene below the contact metal, 20 and ion beam irradiation. 21,22 A more deterministic approach is the formation of "edge"-contacts, where the graphene under the contact is partially removed by lithographic methods to enable the formation of covalent bonds between graphene and metal. This idea was proposed by means of an ingenious contact geometry by Wang 23 . Subsequently, the partial removal of the graphene under the contact by lithography, plasma or ion bombardment allowed a more versatile contact design. In particular, Smith et al. 24 investigated edge patterning of graphene with rectangular cuts under palladium (Pd) and copper (Cu) contacts with the transfer length method (TLM). The conclusion of this study was extended by Park et a...

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“…several questions remain open in this field including the fine control of the separation distance metal-graphene; the perturbation of graphene's bandstructure due to the presence of metals [32,45] (see Supporting Information Note 5) including the possible creation of defects due to the metal deposition; the effect of metal granularity [54] in the dipole created at metal-graphene interfaces or undesired residual current being injected from the graphene to the metal in some cases (see Supporting Information Note 7). Finally, our results can be extended to other 2D materials [41,42] and are relevant to other applications where the spatial extent of lateral p-n junctions at metalgraphene interfaces is important, including contacts [36][37][38][39] and photodetectors [43,44]. We solve the non-linear Poisson's equation, described by Eq.…”

Section: Discussionmentioning

confidence: 99%

“…resulting from the charge redistribution at these one-dimensional interfaces [33,37,45], where ( ) is a consequence of both, the electrostatic gating due to the back gate potential g V tuning the overall Fermi level F E within the entire graphene device and the asymmetry of the chemical potential along the graphene sheet due to the presence of the metal island ( Fig. 2b).…”

Section: Electrostatic Model Of P-n Junctions At Metal-graphene Intermentioning

confidence: 99%

Electrostatics of metal–graphene interfaces: sharp p–n junctions for electron-optical applications

Chaves¹,

Jiménez²,

Santos

et al. 2019

Nanoscale

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Creation of sharp lateral p-n junctions in graphene devices, with transition widths w well below the Fermi wavelength λ F of graphene's charge carriers, is vital to study and exploit these electronic systems for electron-optical applications. The achievement of such junctions is, however, not trivial due to the presence of a considerable out-of-plane electric field in lateral p-n junctions, resulting in large widths. Metal-graphene interfaces represent a novel, promising and easy to implement technique to engineer such sharp lateral p-n junctions in graphene field-effect devices, in clear contrast to the much wider (i.e. smooth) junctions achieved via conventional local gating. In this work, we present a systematic and robust investigation of the electrostatic problem of metal-induced lateral p-n junctions in gated graphene devices for electron-optics applications, systems where the width w of the created junctions is not only determined by the metal used but also depends on external factors such as device geometries, dielectric environment and different operational parameters such as carrier density and temperature. Our calculations demonstrate that sharp junctions (w << λ F )can be achieved via metal-graphene interfaces at room temperature in devices surrounded by dielectric media with low relative permittivity (<10). In addition, we show how specific details such as the separation distance between metal and graphene and the permittivity of the gap in-between plays a critical role when defining the p-n junction, not only defining its width w but also the energy shift of graphene underneath the metal. These results can be extended to any two-dimensional (2D) electronic system doped by the presence of metal clusters and thus are relevant for understanding interfaces between metals and other 2D materials.

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A physics-based model of gate-tunable metal–graphene contact resistance benchmarked against experimental data

Cited by 37 publications

References 26 publications

Electrical properties of graphene-metal contacts

Electrical properties of graphene-metal contacts

Ultralow Specific Contact Resistivity in Metal–Graphene Junctions via Contact Engineering

Electrostatics of metal–graphene interfaces: sharp p–n junctions for electron-optical applications

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