▎ 摘　　要

We discuss the residual carrier density (n*) near the Dirac point (DP) in graphene estimated by quantum capacitance (C-Q) and conductivity (sigma) measurements. The C-Q at the DP has a finite value and is independent of the temperature. A similar behavior is also observed for the conductivity at the DP, because their origin is residual carriers induced externally by charged impurities. The n* extracted from C-Q, however, is often smaller than that from sigma, suggesting that the mobility in the puddle region is lower than that in the linear region. The C-Q measurement should be employed for estimating n* quantitatively. (C) 2013 AIP Publishing LLC.