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 XXh and of mixed heavy-light-hole XXm biexcitons showing binding energies of Δh=4.8meV and Δm=2.8meV is identified by polarization selection rules. The coherent dynamics of the FWM response and the observed FWM intensity ratio between the XXh and XXm biexciton-induced nonlinear signals are in agreement with the solution of an extended optical Bloch equation

Many-body theory for II–VI semiconductor laser media

We study the interplay between resonant cavity, carrier-quantum confinement and many-body effects by means of a Keldysh Green’s function approach which treats the relevant quasi-particles (photons, carriers and plasmons) within a fully quantum-mechanical footing. In order to consistently describe the gain lineshape and spectral position of lasing, it is demonstrated that both Coulomb effects within mean-field contributions and higher order many-body effects as screening, diagonal and off-diagonal dephasing and renormalization of the interband energy have to be taken into account. Strong compensation between diagonal and off-diagonal contributions is found. Numerical results for II–VI heterostructures under quasi-equilibrium conditions and for temperatures ranging from 100 K to 300 K are compared with recent experimental findings. Solving the kinetic equation of photons transient spectral and temporal oscillations experimentally observed in the laser emission are shown to result from memory effects