Measurement of binding energy of negatively charged excitons in GaAs/Al0.3Ga0.7As quantum wells

We report a photoluminescence study of electron-hole complexes in specially designed semiconductor heterostructures. Placing a remote dilute layer of donors at different distances d from the quantum well (QW) leads to the transformation of luminescence spectra of neutral (X) and negatively charged (X^-) excitons. The onset of an additional spectral line and its energy dependence on d allows us to unambiguously relate the so-called X^- trion state with charged excitons bound on charged donors in a barrier. The results indicate the overestimation in free-trion binding energies from previous studies of GaAs/Al_0.3Ga_0.7As quantum wells and give their corrected values for QWs of width 200 and 300Å in the limiting case of infinitely distant donors.