Evidence of the role of contacts on the observed electron-hole asymmetry in graphene

Abstract

We perform electrical transport measurements in graphene with several sample geometries. In particular, we design ``invasive'' probes crossing the whole graphene sheet as well as ``external'' probes connected through graphene side arms. The four-probe conductance measured between external probes varies linearly with charge density and is symmetric between electron and hole types of carriers. In contrast measurements with invasive probes give a strong electron-hole asymmetry and a sub-linear conductance as a function of density. By comparing various geometries and types of contact metal, we show that these two observations are due to transport properties of the metal/graphene interface. The asymmetry originates from the pinning of the charge density below the metal, which thereby forms a p-n or p-p junction depending on the polarity of the carriers in the bulk graphene sheet. Our results also explain part of the sub-linearity observed in conductance as a function of density in a large number of experiments on graphene, which has generally been attributed to short-range scattering only.

4 pages, 5 figures, Supplementary information will come soon

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• Contact resistance and shot noise in graphene transistors
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• Determination of Carrier Type Doped from Metal Contacts to Graphene by Channel-Length-Dependent Shift of Charge Neutrality Points
• Theory of the spontaneous buckling of doped graphene
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• Experimental signature of bandgap opening in bilayer graphene at metal contacts
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• Ultra-low doping and local charge variation in graphene measured by Raman: experiment and simulation