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 $\left(X\right)$ and negatively charged $\left(X^{-}\right)$ 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 $\text{GaAs}/{\text{Al}}_{0.3}{\text{Ga}}_{0.7}\text{As}$ quantum wells and give their corrected values for QWs of width 200 and $300\text{Å}$ in the limiting case of infinitely distant donors.

• Received 29 January 2009

DOI:https://doi.org/10.1103/PhysRevB.79.233306