Charged Impurity Scattering in Bilayer Graphene

Materials Research Science and Engineering Center and Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, MD, 20742, USA We have examined the impact of charged impurity scattering on the charge carrier transport in bilayer graphene in ultra-high vacuum (UHV) at low temperatures. Bilayer graphene sheets are mechanically exfoliated on Si/SiO$_{2}$ substrates, and the number of layers is verified by micro-Raman spectroscopy. Charged impurity density is varied over a wide range (up to 2x10$^{13}$ cm$^{-2})$ by deposition of potassium atoms on clean bilayer graphene in UHV. At a gate-induced charge carrier density of 4.3 x 10$^{12}$ cm$^{-2}$, the mobility is inversely proportional to the charged impurity density $\mu $ = 5x10$^{15}$ V$^{-1}$s$^{-1}$/$n_{imp}$. Surprisingly, the coefficient relating $\mu $ to 1/$n_{imp}$ has a similar magnitude to that for single-layer graphene, indicating a similar strength for charged impurity scattering at this carrier density. The magnitude of charged impurity scattering, as well as the implications for the source of disorder in undoped bilayer graphene, will be discussed in the context of Boltzmann transport theory.