Measurement of binding energy of negatively charged excitons in GaAs/AlGaAs quantum wells

TL;DR

This study measures the binding energy of negatively charged excitons in GaAs/AlGaAs quantum wells using photoluminescence, revealing corrected values that differ from previous estimates and clarifying their relation to charged donors.

Contribution

It provides the first direct measurement of negatively charged exciton binding energies in GaAs/AlGaAs quantum wells and clarifies their relation to donor-bound states.

Findings

Charged excitons are bound to donors in barriers.

Corrected binding energy values are lower than previous estimates.

Spectral lines depend on donor distance d.

Abstract

We report a photoluminescence study of electron-hole complexes in specially designed semiconductor heterostructures. Placing a remote dilute layer of donors at different distances \itshape d \normalfont from the quantum well 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 \itshape d \normalfont 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$_{0.3}$Ga$_{0.7}$As quantum wells, and give their corrected values for QWs of width 200 and 300 \AA \space in the limiting case of infinitely distant donors.