Exceptional Charge Transport Properties of Graphene on Germanium

The excellent charge transport properties of graphene suggest a wide range of application in analog electronics. While most practical devices will require that graphene be bonded to a substrate, such bonding generally degrades these transport properties. In contrast, when graphene is transferred to Ge(001) its conductivity is extremely high and the charge carrier mobility derived from the relevant transport measurements is, under some circumstances, higher than that of freestanding, edge-supported graphene. We measure a mobility of similar to 5 x 10(5) cm(2) V-1 s(-1) at 20 K, and similar to 10(3) cm(2) V-1 s(-1) at 300 K. These values are close to the theoretical limit for doped graphene. Carrier densities in the graphene are as high as 10(14) cm(-2) at 300 K.