Photoluminescence and reflectance studies of negatively charged excitons in GaAs/Al0.3Ga0.7As quantum-well structures

We report the results of a systematic photoluminescence and reflectance stu dy of negatively charged excitons (X-) in several GaAs/AlxGa1-xAs quantum w ell structures. Samples are either doped n-type in the wells or not intenti onally doped, and thus the appearance of X- (present in modulation doped sa mples) is not expected. The combination of the two spectroscopies allowed u s to explore the possible mechanisms responsible for the formation of the X - complex, in all cases the X- signature is related to excess electrons in the wells. These results provide positive evidence that the original identi fication of the X- photoluminescence feature is correct.