Binding energy of charged excitons in ZnSe-based quantum wells

Excitons and charged excitons (trions) are investigated in ZnSe-based quantum well structures with (Zn,Be,Mg)Se and (Zn,Mg)(S,Se) barriers by means of magneto-optical spectroscopy. Binding energies of negatively ${(X}^{-})$ and positively ${(X}^{+})$ charged excitons are measured as functions of quantum well width, and free carrier density and in external magnetic fields up to 47 T. The binding energy of $X^{-}$ shows a strong increase from 1.4 to 8.9 meV with decreasing quantum well width from 190 to $29\hspace{0.5em}\AA .$ The binding energies of $X^{+}$ are about 25% smaller than the $X^{-}$ binding energy in the same structures. The magnetic field behavior of $X^{-}$ and $X^{+}$ binding energies differ qualitatively. With growing magnetic field strength, $X^{-}$ increases its binding energy by 35–150%, while for $X^{+}$ it decreases by 25%. Zeeman spin splittings and oscillator strengths of excitons and trions are measured and discussed.