OPTICS OF EXCITONIC MOLECULES IN SEMICONDUCTORS AND SEMICONDUCTOR MICROSTRUCTURES

A bipolariton concept of an excitonic molecule in direct-band-gap semi conductors is reviewed. The bipolariton model interprets a molecule as two quasi-bound polaritons provided that both the exciton-exciton Cou lombic 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 c oncept 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 exciton ic molecules, molecule-mediated optical Stark effect and other coheren t processes which effectively involve excitonic molecules, and polarit on solitons coupled through the molecule state. (C) 1998 Elsevier Scie nce B.V. All rights reserved.