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

Low-temperature magnetophotoluminescence studies of negatively charged exci tons (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 el ectron gases an highly spin polarized even at low magnetic fields, througho ut the entire range of electron densities studied (5x10(10) to 6.5x10(11) c m(-2)). This spin polarization has a pronounced effect on the formation and energy of X-s(-), with the striking result that the trion ionization energ y (the energy separating X-s(-) from the neutral exciton) follows the tempe rature- and magnetic field-tunable Fermi energy. The large Zeeman energy de stabilizes X-s(-) at the nu=1 quantum limit, beyond which a separate photol uminescence peak appears and persists to 60 T, suggesting the formation of spin-triplet charged excitons.