"ELECTRICAL CONTACTS TO TWO-DIMENSIONAL MATERIALS: WHEN LESS IS MORE"

Who: Xavier Cartoixà (Dept. d'Enginyeria Electrònica, Universitat Autònoma de Barcelona)

Place: Donostia International Physics Center

Date: Friday, 24 July 2015, 12:00

In order for graphene and other two-dimensional materials to become competitive players amongst the myriads of electronic devices, one of the main technological hurdles that must be overcome is achieving a low contact resistance (Rc) so that high frequency performance is not compromised [1]. For graphene, it is often quoted that an Rc value lower than 100 ???m is desirable, while larger values are thought to be a limiting factor on the graphene field effect transistor performance [2,3]. Recent experiments have achieved this landmark value with a top contact geometry [4]. On the other hand, an edge contact has been shown experimentally to achieve contact resistances with similar or lower values than most top contacts [5], challenging the conventional wisdom that having a large contact area will result in a decreased value of the contact resistance.

We will argue that ballistic electron injection into graphene (or any other 2D material) is basically a perimeter-dependent phenomenon, dependent only on the atomistic details of the graphene-metal configuration at the edge of the metal, and pretty much independent on the amount of metal-2DM overlap.

Our arguments are supported by first principles calculations of the conductance of a model {Ni,Al,Pd}(111)/Graphene contact, where the type of binding (chemi- vs physisorbed) relates to the size of the fluctuations of the transmission curves, but does not show any clear dependence on the amount of overlap. In fact, having a large overlapping region between the metal and the 2D material may be detrimental to the goal of a low contact resistance.

We acknowledge financial support by the Spanish Ministerio de Economía y Competitividad under Projects Nos. TEC2012-31330 and FIS2010-21883 and by Generalitat Valenciana under Grant PROMETEO/2012/011. We also acknowledge computational support from the CCC of the Universidad Autónoma de Madrid. Also, the research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement No. 604391 Graphene Flagship.

References

[1] J. S. Moon and D. K. Gaskill, IEEE Trans. Microwave Theory Tech. 59, (2011) 2702.
[2] A. Venugopal, L. Colombo and E. M. Vogel, Appl. Phys. Lett. 96, (2010) 013512.
[3] Bo-Chao Huang, Ming Zhang, Yanjie Wang and Jason Woo, Appl. Phys. Lett. 99, (2011) 032107.
[4] J. S. Moon, M. Antcliffe, H. C. Seo, D. Curtis, S. Lin et al., Appl. Phys. Lett. 100, (2012) 203512.
[5] L. Wang, I. Meric, P. Y. Huang, Q. Gao, Y. Gao et al., Science 342, (2013) 614.

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