Field-modulated diffusivity of excitons in coupled asymmetric quantum wells

Using time- and space-resolved photoluminescence spectroscopy, we have measured the lateral in-plane transport of spatially direct and indirect excitons in coupled asymmetric GaAs quantum wells. The quantum wells were grown in the intrinsic region of a p-i-n structure to allow the application of an electric field normal to the growth plane. At 4.2 K, spatial transport measurements at zero electrical bias show that the direct excitons become localized (immobile) and display a 0.8-meV spectral shift to lower energies. With increasing bias, the localization is reduced and eventually disappears as the excitons increasingly become spatially indirect. At higher bath temperatures (20–60 K), we find no spatial localization, nor does the exciton peak shift to lower energies. Furthermore, the spatial transport properties are not affected by the changes in the field bias. We discuss our results in terms of interface-roughness scattering arising from the different interfacial qualities on either side of the GaAs quantum well.