Optically induced electric-field domains by bound-to-continuum transitions in $n$-type multiple quantum wells

We report on the experimental evidence of electric-field domain formation induced by the intersubband photocurrent in $n$-type $\mathrm{GaAs}/{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ multiple quantum wells. The domain structure manifests itself by a plateaulike regime in the voltage dependence of the total current under infrared illumination. Domain formation is caused by a negative differential field dependence of the photoexcited carrier mean free path. The domain structure does not exist in the dark since the increase of the thermally excited carrier density in the continuum overrides the decrease of the mean free path.