Formation and phase relaxation of negatively charged excitons in ZnSe single quantum wells

We investigate the formation, interaction, and dephasing of negatively char ged excitons (trions) in ZnSe/Zn0.9Me0.1Se single quantum wells by polariza tion, intensity, and temperature dependent spectrally resolved transient fo ur-wave mixing. The trion transition shows a binding energy of 2.8 meV and is discriminated from the biexciton by its polarization dependence. The coh erent dynamics of the four-wave mixing response is in fair agreement with c alculations based on extended optical Bloch equations. Temperature dependen t measurements exhibit a significant enhancement of the exciton dephasing b elow 40 K due to the presence of trions and incoherent electrons which are optically excited from the GaAs substrate and captured by the quantum well. [S0163-1829(99)11347-X].