Dynamics of Exciton Formation and Relaxation in Semiconductors
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Optical excitation above the band gap of a semiconductor generates hot carrier distributions which subsequently relax towards an equilibrium with the crystal lattice. Simultaneously, electron-hole (e-h) pairs may undergo assisted transitions to excitonic bound states. These free excitons are created with large center-of-mass wave vectors, K: to become optically active they have to be scattered into states with K ≈ 0 and s-symmetry by inelastic collisions. The time-resolved measurement of the resulting luminescence1 provides information about these intrinsic processes of exciton formation and relaxation. However, the interpretation of the experiments is difficult due to the various competing interactions of free carriers and excitons and a kinetic model of the system is needed.