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

Abstract

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...

Dependable Contact Related Parameter Extraction in Graphene–Metal Junctions

“…To achieve low contact resistivity, nanostructuring or engineering of graphene under the contact metals have displayed some potential. [24][25][26] Nevertheless, reported values of R C found in literature vary considerably, [27][28][29][30] which can be attributed to intrinsic factors such as the quality of graphene layers, work functions of the metals or doping of graphene, and to extrinsic factors such as specific fabrication procedures. However, there is also a debate on the applicability of standard measurement and extraction methods to obtain dependable and correct R C values.…”

Large Responsivity of Graphene Radiation Detectors with Thermoelectric Readout: Results of Simulations

“…The contact resistance does not seem to be a big problem for the low-ohmic edge contacts, which are possible for graphene encapsulated in both hBN [30] and Parylene [20,31], the latter being important for scaling up the device fabrication. Also, the contact resistance can be effectively reduced by increasing the perimeter of contact even for a non-encapsulated graphene [32]. Finally, the capacitive coupling of antennas to graphene, where the contact resistance does not play any role for the open-circuit TEP readout, has recently been realized [21].…”

Graphene in 2D/3D Heterostructure Diodes for High Performance Electronics and Optoelectronics

“…Carrier emission from graphene edges is known to be very effective in reducing the resistance of electrical contacts between graphene and metals. [ 39–41 ] In a similar fashion, electron emission from the graphene into/across the insulator in MIG diodes can be increased considerably if it happens only through a 1D graphene edge. In this geometry, shown in Figure 3d, the junction area is determined only by the monoatomic thickness of graphene of ≈0.3 nm and the width of the contact, resulting in an exceptionally small junction capacitance.…”