Interaction of an electron gas with photoexcited electron–hole pairs in modulation-doped GaAs and CdTe quantum wells

The nature of the correlated electron gas and its response to photo-injected electron–hole pairs in nominally undoped and modulation-doped multiple quantum-well structures was studied by experiment and theory, revealing a new type of optically active excitation, magnetoplasmons bound to a mobile valence hole. These excitations are blue-shifted from the corresponding transition of the isolated charged magnetoexciton X−. The observed blue-shift of X− is larger than that of two-electron negative donor D−, in agreement with theoretical predictions.