Ac ballistic transport in a two-dimensional electron gas measured inGaAs∕AlGaAsheterostructures

Abstract

We measure the crossover from diffusive to ballistic transport as a function of frequency in dc contacted high-mobility two-dimensional electron gas structures in $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ heterostructures at GHz frequencies. By systematically measuring samples of varying mobility we demonstrate that the crossover frequency scales with mobility as predicted by the Drude model. We find the ohmic contact impedance to be real and independent of frequency for samples with mobility higher than $500\phantom{\rule{0.2em}{0ex}}000\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$, while there is a significant capacitive component in parallel with the contact resistance for lower mobility samples.