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 (5×10¹⁰ to 6.5×10¹¹ cm^-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 ν=1 quantum limit, beyond which a separate photoluminescence peak appears and persists to 60 T, suggesting the formation of spin-triplet charged excitons.