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The origins and limits of metal–graphene junction resistance


A high-quality junction between graphene and metallic contacts is crucial in the creation of high-performance graphene transistors. In an ideal metal–graphene junction, the contact resistance is determined solely by the number of conduction modes in graphene. However, as yet, measurements of contact resistance have been inconsistent, and the factors that determine the contact resistance remain unclear. Here, we report that the contact resistance in a palladium–graphene junction exhibits an anomalous temperature dependence, dropping significantly as temperature decreases to a value of just 110 ± 20 Ω µm at 6 K, which is two to three times the minimum achievable resistance. Using a combination of experiment and theory we show that this behaviour results from carrier transport in graphene under the palladium contact. At low temperature, the carrier mean free path exceeds the palladium–graphene coupling length, leading to nearly ballistic transport with a transfer efficiency of ~75%. As the temperature increases, this carrier transport becomes less ballistic, resulting in a considerable reduction in efficiency.

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Figure 1: Determination of palladium–graphene contact resistance using the transfer length method (TLM).
Figure 2: Temperature dependence of contact resistance.
Figure 3: Carrier transport processes at the palladium–graphene junction and gate dependence of Dirac-point energies in graphene under palladium and in the channel.
Figure 4: Transmission efficiency TMG, determined using Matthiessen's rule.


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The authors are grateful to B. Ek and J. Bucchignano for technical assistance and the Defense Advanced Research Projects Agency for partial financial support through the Carbon Electronics for Radio-frequency Applications program (contract FA8650-08-C-7838). F.X. is indebted to C.Y. Sung for his encouragement. V.P. gratefully acknowledges stimulating discussions with J. Tersoff.

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Correspondence to Fengnian Xia or Phaedon Avouris.

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Xia, F., Perebeinos, V., Lin, Ym. et al. The origins and limits of metal–graphene junction resistance. Nature Nanotech 6, 179–184 (2011).

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