Properties of Metal–Graphene Contacts

We present a study on the metal-graphene contact properties. Utilizing a dual-gate field-effect transistor device, an energetic separation between the Fermi level and the Dirac point in the contact areas can be adjusted deliberately by applying an appropriate front-gate voltage that acts only on the channel. This front-gate voltage is compensated by an opposite large-area back-gate voltage, thereby mimicking the metal induced doping effect. A back-gate voltage sweep enables identifying two distinct resistance peaks-a result of the combined impact of the graphene cones in the contact and in the channel region. Comparing our experimental data with simulations allows extracting the coupling strength between metal and graphene and also estimating the magnitude of the metal-induced doping concentration in the case of palladium contacts. In contrast to conventional metal-semiconductor contacts, our simulations predict a decreased on-current for increased coupling strength in graphene field-effect transistors.