Mixed biexcitons in single quantum wells

Biexcitonic complexes in a ZnSe single quantum well are investigated by spectrally resolved four-wave mixing (FWM). The formation of heavy-heavy-hole ${\mathrm{XX}}_h$ and of mixed heavy-light-hole ${\mathrm{XX}}_m$ biexcitons showing binding energies of ${\Delta }_h=4.8\mathrm{}\mathrm{meV}$ and ${\Delta }_m=2.8\mathrm{}\mathrm{meV}$ is identified by polarization selection rules. The coherent dynamics of the FWM response and the observed FWM intensity ratio between the ${\mathrm{XX}}_h$ and ${\mathrm{XX}}_m$ biexciton-induced nonlinear signals are in agreement with the solution of an extended optical Bloch equation.