Effect of charged impurities on the thermoelectric power of graphene near the Dirac point

In graphene devices with a varying degree of disorders as characterized by their carrier mobility and minimum conductivity, we have studied thermoelectric power along with electrical conductivity over a wide range of temperatures. We have found that the Mott relation fails in the vicinity of the Dirac point in high-mobility graphene. By properly taking account of high-temperature effects, we have obtained good agreement between the Boltzmann transport theory and our experimental data. In low-mobility graphene where the charged impurities induce relatively high residual carrier density, the Mott relation holds at all gate voltages.