Theoretical Study Of The Transport Properties Of Metal-graphene Contacts

Graphene attracts a large number of scientists’ attention since its first discovery inlab due to its unique physical properties, which is undoubtedly the superstar material in thefield of science. Graphene is expected to be applied in many fields, among which theapplication of graphene in nanoelectronic devices is very promising. In the past40years,the silicon electronic devices have been widely used in computers, communicationsequipments and other equipments and greatly changed our life. However, as the scale ofelectronic devices continue to decrease to be close to nano-scale, the silicon electronicdevices would reach their technology limits. Graphene owns many superior electronicproperties, such as low resistance, ten times larger carrier mobility than Si, and large Fermivelocity. These superior electronic properties make graphene to be expected to be thecandidate material of future nanoelectronic devices. However, one key problem in theapplication of graphene needed to be solved is the large contact resistance in grapheneelectronic devices, for the contact resistance would greatly affect the key performance ofgraphene electronic devices, such as the transconductance (gm), on-current (Ion), andcut-off frequency (fT).Deep research on the properties of interface between carbon nanostructures with πelectrons and metal surfaces is necessary to overcome the contact resistance to get highperformance the nanoelectronic devices. The metals, which are commonly used aselectrodes of graphene nanoelectronic devices, can be divided into two types according tothe interacting strength with graphene: strongly and weakly adsorbed metals. In this project,we systematically studied the effects of different factors, such as different contactconfigurations, graphene terminations, contact area and point defects, on the interactionsand transport properties of six types of metal (Au, Ag, Cu, Pt, Pd and Ni)-graphenecontacts. We found that the metals which form strongly interaction with graphene could form lower contact resistance with graphene due to the efficiently hybridization couplingwith the graphene’s π orbitals. What’s more, by considering the graphene defects’effect onthe transport properties of these contacts, we found that the vacancy of graphene couldincrease the coupling between graphene and metals and decrease the contact resistance,which was similar to the unpassivated graphene edge. In general, the defects of grapheneshowed little enhancement of conductance when forming contact with strongly interactingmetals. These discussions and conclusions would offer experimentalists evidences andreferences to fabricate graphene electronic devices with higher performance.