Mobility anisotropy in monolayer black phosphorus due to scattering by charged impurities

We explore the charged-impurity-scattering-limited mobility of electrons and holes in monolayer black phosphorus (BP), a highly anisotropic material. Taking full account of the anisotropic electronic structure in effective mass approximation, the zero-temperature momentum relaxation time and the charge carrier mobility are calculated based on the Boltzmann transport equation. For carrier densities accessible in experiments, we obtain anisotropy ratios of 3-4. These results are somewhat larger than mobility anisotropy ratios determined experimentally for multilayer BP samples, but due to the complex dependence of the scattering rates on the anisotropy, they are strikingly smaller than the effective mass ratios.