Magnetophotoluminescence of negatively charged excitons in narrow quantum wells

We present the results of photoluminescence experiments on the negatively charged exciton X^- in GaAs/AlₓGa_1-xAs quantum wells (QW) in high magnetic fields (<~50T). Three different QW widths are used here: 100, 120, and 150. All optically allowed transitions of X^- are observed, enabling us to experimentally verify its energy-level diagram. All samples behave consistently with this diagram. We have determined the binding energy Eb of the singlet and triplet state of X^- between 23 and 50 T for the 120 and 150QW, while only the triplet Eb is observed for the 100QW. A detailed comparison with recent theoretical calculations shows an agreement for all samples across this entire field range.