Charge transport in graphene doped with diatomic halogen molecules (I2, Br2) near Dirac point

We have investigated the transport properties of monolayer graphene doped with halogen molecules, iodine and bromine. For these doping, the charge neutrality point shifts to the hole carrier regime indicating p-type doping, and the carrier mobility is reduced. As compared to doping with other dopants, however, the reduction of the mobility is much weaker for doping with halogen molecules. Also, the minimum conductivities at the charge neutrality point are enhanced with subsequent doping for the monolayer graphene, in strong contrast to the cases with other dopants. When the graphene layer was doped selectively by covering its edge with a polymer layer, such unconventional behaviors were not observed any more. These observations can be understood that intercalated halogen molecules between the graphene layer and the underlying substrate leads to screening of charged impurities embedded in SiO2 substrate. Halogen molecules can be effective dopants for the graphene monolayer which changes the carrier concentration without significant degrading of the mobility.