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In this work, the focus of the time-resolved experiments is on the modulationdoped single-well structures. These are of high-quality but have the disadvantage that they only exhibit weak Four Wave Mixing signals. Up to now, only results on the doped multiple well structures exist. A main part of the Four Wave Mixing experiments focuses on the two-dimensional electron gas at filling
factor ? = 1. With increasing magnetic field a step-like increase of the dephasing time at ? = 1 is found for the light-hole like transition. Moreover, it is deduced that the dephasing time not only depends on the electron states but also on the coupling between the hole states. A sample structure is introduced, specially designed for our time-resolved experiments, that provides for weak signals the necessary prealignment of the setup. On these samples, also circular polarization resolved measurements could be performed. In these experiments, no signature of filling factor ? = 1 is resolved in the dephasing time. From the dephasing times of the excitons, it is concluded that the charged exciton is probably not localized in our sample. Moreover, an interchanged beating pattern of the neutral excitons with the triplet state is observed.
