Optics of excitonic molecules in semiconductors and semiconductor microstructures

A bipolariton concept of an excitonic molecule in direct-band-gap semiconductors is reviewed. The bipolariton model interprets a molecule as two quasi-bound polaritons provided that both the exciton-exciton Coulombic interaction and the exciton-photon coupling (polariton effect) are treated simultaneously and beyond a low-order perturbation theory. The molecule-mediated optics is reformulated within the bipolariton concept for bulk semiconductors (e.g., CuCl and CdS) and semiconductor microstructures (e.g., GaAs quantum wells and wires). We discuss such phenomena as two-photon absorption and four-wave-mixing due to excitonic molecules, molecule-mediated optical Stark effect and other coherent processes which effectively involve excitonic molecules, and polariton solitons coupled through the molecule state. (C) 1998 Elsevier Science B.V. All rights reserved.