COHERENT VERTICAL TRANSPORT OF EXCITONS IN MULTIPLE-QUANTUM WELLS

A theory for the coherent vertical radiative and radiationless transport of excitons in multiple quantum wells is presented. The coupling between distinct quantum wells is via the coherent emission and reabsorption of photons, and is treated within a polariton formalism. We obtain closed-form expressions for the correlation functions describing radiative and radiationless transport in two physically relevant limiting cases-the instantaneous limit where retardation is neglected (appropriate for large in-plane wave-vector excitations) and the long-wavelength approximation (appropriate for structure periods much less than the optical wavelength corresponding to the transition from the exciton to the crystal ground state). We find that the long-range character of the interwell coupling in the latter case gives rise to fast excitation transfer compared with the former case where the coupling is short ranged. © 1995 The American Physical Society.