Reversible doping of graphene field effect transistors by molecular hydrogen: the role of the metal/graphene interface

Abstract In this work, we present an investigation regarding how and why molecular hydrogen (H ₂ ) changes the electronic properties of graphene field effect transistors (GFETs). We demonstrate that interaction with H ₂ leads to local doping of graphene near of the graphene-contact heterojunction. We also show that such interaction is strongly dependent on the characteristics of the metal-graphene interface. By changing the type of metal in the contact, we observe that Ohmic contacts can be strongly or weakly electrostatically coupled with graphene. For strongly coupled contacts, the signature of the charge transfer effect promoted by the contacts results on asymmetric ambipolar conduction, and such asymmetry can be tunable under interaction with H ₂ . On the other hand, for contacts weakly coupled with graphene, the hydrogen interaction has a more profound effect. In such a situation, the devices show a second charge neutrality point (CNP) in graphene transistor transfer curves (a double-peak response) upon H ₂ exposure. We propose that this double-peak phenomenon arises from the decoupling of the work function of graphene and that of the metallic electrodes induced by the H ₂ molecules. We also show that the gas-induced modifications at the metal-graphene interface can be exploited to create a controlled graphene p-n junction, with considerable electron transfer to graphene layer and significant variation in the graphene resistance. These effects can pave the way for a suitable metallic contact engineering providing great potential for the application of such devices as gas sensors.