Inter-exciton exchange interaction and nonlinear luminescence polarizationdynamics in III-V semiconductor quantum wells

The effects of the inter-exciton exchange interaction in the time evolution of the exciton luminescence intensity and polarization in III-V semiconduc tor quantum wells are investigated theoretically The luminescence dynamics in the resonant and high density excitation regime is simulated with a set of nonlinear rate equations for the occupation numbers of a finite set of e xciton spin states. and studied as function of the polarization and intensi ty of the exciting pulse. The spin flip transitions are driven by both intr a- and inter-exciton exchange interaction. Two contributions to the latter are included in the simulation, namely the spin mixing in the symmetrized b iexciton state and the spin dependent free exciton-exciton scattering. It i s found that the fast decay observed experimentally at sufficient high exci tation intensities, in both luminescence intensity and polarization, is rep roduced with reasonable values for the relaxation times only when both cont ributions to the inter-exciton exchange interaction are turned on.