We theoretically calculate and compare the single particle relaxation time (τₛ) defining the quantum level broadening and the transport scattering time (τₜ) defining the Drude conductivity in two-dimensional (2D) graphene layers in the presence of screened charged impurity scattering and short-range defect scattering. We find that the ratio τₜ∕τₛ strongly increases with increasing kFzᵢ and κ, where kF, zᵢ, and κ are, respectively, the Fermi wave vector, the separation of the substrate charged impurities from the graphene layer, and the background lattice dielectric constant. A critical quantitative comparison of the τₜ∕τₛ results for graphene with those for the corresponding modulation-doped semiconductor structures is provided, showing significant differences between these two 2D carrier systems.
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Hwang et al. (2008) studied this question.