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

B. Huard (1) , N. Stander (1) , J. A. Sulpizio (1) , D. Goldhaber-Gordon (2)

1 Department of Physics
2 Physics Department [Stanford]

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.

Domaines: Science des matériaux [cond-mat.mtrl-sci]

B. Huard, N. Stander, J. A. Sulpizio, D. Goldhaber-Gordon. Evidence of the role of contacts on the observed electron-hole asymmetry in graphene. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2008, 78, pp.121402. ⟨hal-00520826⟩