Magnetophotoluminescence of negatively charged excitons in narrow quantum wells

We present the results of photoluminescence experiments on the negatively charged exciton $X^{-}$ in $\mathrm{GaAs}/{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells (QW) in high magnetic fields $(<~50\mathrm{T}).\mathrm{}$ Three different QW widths are used here: 100, 120, and $150\AA .$ 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 $E_b$ of the singlet and triplet state of $X^{-}$ between 23 and 50 T for the 120 and $150\AA \mathrm{QW},$ while only the triplet $E_b$ is observed for the $100\mathrm{\AA }\mathrm{QW}.$ A detailed comparison with recent theoretical calculations shows an agreement for all samples across this entire field range.