Coherence Effects on the Exciton Radiative Recombination in Quantum Wells
Low temperature luminescence of quantum wells is strongly dominated by excitonic effects . The first reason for this abrupt change, from 3D to 2D systems, lies in the breakdown of the translational symmetry which modifies the usual picture of polariton states (see Hopfield ). In 3D systems, coupling of the exciton to photons does not lead directly to absorption or to light emission but to stable states of the system. On the contrary, for excitons confined in two dimensions, coupling to the photon field leads to a finite lifetime of those excitons with a wavevector | k | <ko=nωo/c  (here ωo is the frequency of the photon at the exciton energy, n the material refractive index and c the speed of light). On the contrary, excitons with k above nωo/c should not recombine at all; this is because conservation of wavevector cannot be obtained in such a case. When computed in the absence of collisions, the decay rate of near k = 0 2D excitons integrates individual dipole elements over the whole quantum well volume. The radiative lifetime of 2D excitons is then very short of the order of 10ps [3–6].
KeywordsRadiative Recombination Rayleigh Scattering Radiative Lifetime Excitation Density Exciton Energy
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