Time-dependent heterointerfacial band bending and quasi-two-dimensional excitonic transport in GaAs structures

Using a time-resolved photoluminescence imaging technique with high spectral, temporal, and spatial resolution, we have directly measured the time- and carrier-density-dependent heterointerfacial band bending in ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ structures, and its influence on quasi-two-dimensional exciton transport. We find the spatially nonuniform band bending induced by laser excitation decays to its static, uniform band bending in $\sim 20\mathrm{ns}.$ Further, we find that the observed transport is initially “driven” by a force originating from the spatially nonuniform band bending arising from photoexcited carrier screening of the built-in heterointerface field and is of very high mobility. This transport becomes diffusive asymptotically in time.