Sheet Resistance Analysis of Interface-Engineered Multilayer Graphene: Mobility Versus Sheet Carrier Concentration.

Both interlayer-undoped and interlayer-doped multilayer graphenes were prepared by the multiple transfers of graphene layers with multiple Cu etching (either dopant-free or doped during etching) and transfer, and the effect of interface properties on the electrical properties of multilayer graphene was investigated by varying the number of layers from 1 to 12. In both the cases, the sheet resistance decreased with increasing number of layers from 700 to 104 Ω/sq for the interlayer-undoped graphene and from 280 to 25 Ω/sq for the interlayer-doped graphene. Further, Hall measurements revealed that the origins of the sheet resistance reduction in the two cases are different. In the interlayer-undoped graphene, the sheet resistance decreased because of the increase in mobility with the addition of inner layers, which has a low carrier density and a high carrier mobility. On the other hand, it decreased because of the increase in sheet carrier density in the interlayer-doped multilayer graphene. The mobility and carrier density variations in both the cases were confirmed by fitting with the model of Hall effect in the heterojunction. In addition, we found that surface property modification by the doping of the top layer and the formation of double-layer graphene with different partial coverages allow the separate control of carrier density and mobility. Our study provides an effective approach for controlling the properties of multilayer graphene for electronic applications.