Effect of back-gate on contact resistance and on channel conductance in   graphene-based field-effect transistors
  We study the contact resistance and the transfer characteristics of back-gated field effect transistors of mono- and bi-layer graphene. We measure specific contact resistivity of ~7kohm*um2 and ~30kohm*um2 for Ni and Ti, respectively. We show that the contact resistance is a significant contributor to the total source-to-drain resistance and it is modulated by the back-gate voltage. We measure transfer characteristics showing double dip feature that we explain as the effect of doping due to charge transfer from the contacts causing minimum density of states for graphene under the contacts and in the channel at different gate voltage. 
A. Di Bartolomeo, S. Santandrea, F. Giubileo, F. Romeo, M. Petrosino,   R. Citro, P. Barbara, G. Lupina, T. Schroeder, A. Rubino
cond-mat.mes-hall cond-mat.mtrl-sci