Impact of process induced defects on the contact characteristics of tigraphene devices

Process induced variation of contact resistance (R _c) in Ti graphene (single or multi-layer) devices is investigated physically and electrically. It is observed that contact resistivity _c is independent of graphene layers when Ti is deposited by e-beam evaporation, while _c increases with the reduction of graphene layers when Ti is deposited by sputtering process. It is proposed that the increased _c can be attributed to the carbon defects (vacancies) created during sputter process in graphene, which is evidenced by Raman spectra. The carbon vacancies would introduce tensile strain in graphene layer, which is responsible for newly-created D band and red shift observed in Raman spectra.