Photoluminescence and reflectance studies of negatively charged excitons in quantum-well structures

We report the results of a systematic photoluminescence and reflectance study of negatively charged excitons (Formula presented) in several (Formula presented) quantum well structures. Samples are either doped n-type in the wells or not intentionally doped, and thus the appearance of (Formula presented) (present in modulation doped samples) is not expected. The combination of the two spectroscopies allowed us to explore the possible mechanisms responsible for the formation of the (Formula presented) complex. In all cases the (Formula presented) signature is related to excess electrons in the wells. These results provide positive evidence that the original identification of the (Formula presented) photoluminescence feature is correct.