Exciton-electron dynamics studied by microwave photoconductivity and photoluminescence in undoped GaAs/Al0.3Ga0.7As quantum wells

We report on a comparative study of the photoinduced microwave absorption (PMA) (contactless photoconductivity) at 35.6 GHz and the photoluminescence (PL) in undoped GaAs/AlxGa1-xAs quantum wells (QW's) having various well widths (50-200 Angstrom). While the PL and its excitation (PLE) spectra probe the excitonic transitions, the PMA intensity and its excitation (PMAE) spectra provide information on unbound electron-hole generation processes. The PMAE spectra show strong (e1:hh1)1S and (e1:1h1)1S excitonic bands. Since these are bound electron-hole transitions that are observed to give rise to free carrier microwave absorption, exciton dissociation processes are involved. A model is presented that explains these bands in terms of Auger-like exciton dissociation at low temperatures and thermal exciton dissociation at high temperatures. We also discuss the effect of carrier and exciton localization in the spatially fluctuating QW potential. [S0163-1829(99)06617-3].