Theory of coherent effects in semiconductors

A microscopic theory is applied to discuss coherent excitation effects in semiconductors. The theory is evaluated to analyze ultrafast absorption changes around the exciton resonance in semiconductor quantum-well structures where the relative strength of the different many-body contributions can be manipulated by proper selection of pump and probe polarizations. For two-band systems and oppositely circular polarization it is shown that Coulombic correlation dynamics dominates the optical response. As a consequence, the optical Stark effect in this configuration corresponds to a red shift of the exciton resonance in striking contrast to the usual atomic-like blue shift. The predictions are confirmed by experiments using high-quality InGaAs quantum-well systems. (C) 1999 Elsevier Science B.V. All rights reserved.