We study the contact resistance and the transfer characteristics ofback-gated field effect transistors of mono- and bi-layer graphene. We measurespecific contact resistivity of ~7kohm*um2 and ~30kohm*um2 for Ni and Ti,respectively. We show that the contact resistance is a significant contributorto the total source-to-drain resistance and it is modulated by the back-gatevoltage. We measure transfer characteristics showing double dip feature that weexplain as the effect of doping due to charge transfer from the contactscausing minimum density of states for graphene under the contacts and in thechannel at different gate voltage.
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