Electron-assisted exciton transfer and long-lived electrons and holes in GaAs/AlxGa1-xAs quantum wells.

Abstract

Long-lived (up to ${10}^{\mathrm{\ensuremath{-}}3}$ s), separately localized electrons and holes are revealed in undoped photoexcited GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wells at T=2 K by their effect on localized excitons. The luminescence spectrum of the resonantly photoexcited (e1:hh1)1S excitons is modified when additional electron-hole pairs are generated, and this modulation decays a very long time after the pair photogeneration terminates. We explain the effect by a localized electron (hole)-exciton interaction that accelerates the exciton transfer from weakly into strongly localized states of the spatially fluctuating in-plane potential. The excess exciton energy is imparted to the interacting electron (hole). This results in an exciton population redistribution and excitation of the localized carriers into delocalized band states. The electron-assisted exciton transfer rate between interface islands that localize the particles is estimated. We find that even under a low excitation level the estimated rate is comparable to the exciton recombination, as well as to the phonon-assisted exciton transfer rate. In addition, we show that the radiative recombination of closely localized electrons and holes (geminate pairs) gives rise to the LO-phonon photoluminescence sideband with a characteristic decay time of ${10}^{\mathrm{\ensuremath{-}}7}$ s. \textcopyright{} 1996 The American Physical Society.