Stability of trions in strongly spin-polarized two-dimensional electron gases

Low-temperature magnetophotoluminescence studies of negatively charged excitons ${(X}_s^{-}$ trions) are reported for n-type modulation-doped ZnSe/Zn(Cd,Mn)Se quantum wells over a wide range of Fermi energy and spin splitting. The magnetic composition is chosen such that these magnetic two-dimensional electron gases are highly spin polarized even at low magnetic fields, throughout the entire range of electron densities studied $(5\mathrm{}\times {10}^{10}$ to $6.5\times {10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$). This spin polarization has a pronounced effect on the formation and energy of $X_s^{-},$ with the striking result that the trion ionization energy (the energy separating $X_s^{-}$ from the neutral exciton) follows the temperature- and magnetic field–tunable Fermi energy. The large Zeeman energy destabilizes $X_s^{-}$ at the $\nu =1\mathrm{}$ quantum limit, beyond which a separate photoluminescence peak appears and persists to 60 T, suggesting the formation of spin-triplet charged excitons.