Scattering mechanism in modulation-doped shallow two-dimensional electron gases

We report on a systematic investigation of the dominant scattering mechanism in shallow two-dimensional electron gases (2DEGs) formed in modulation-doped GaAs/AlxGa1−xAs heterostructures. The power-law exponent of the electron mobility versus density, μ∝nα, is extracted as a function of the 2DEG’s depth. When shallower than 130 nm from the surface, the power-law exponent of the 2DEG, as well as the mobility, drops from α≃1.65 (130 nm deep) to α≃1.3 (60 nm deep). Our results for shallow 2DEGs are consistent with theoretical expectations for scattering by remote dopants, in contrast to the mobility-limiting background charged impurities of deeper heterostructures.