Optics and magneto-optics of coexisting localized and free holes in GaAs quantum wells

The photoluminescence and photoluminescence excitation spectra have been studied in two twin GaAs quantum wells containing a two-dimensional electron gas with high density and high mobility. One of the wells includes a few Be acceptors in a δ-layer at the center of the well, which localize part of the photocreated holes. In the other well the holes are free. Comparison of the optical spectra of both samples shows that the Fermi-edge singularity in emission is only observed for localized holes, while in excitation spectra both Be-bound- and free holes display the same singularity. Thus, localization of holes appears to be relevant mainly by its effect on the final-state density. Magneto-optical measurements confirm the presence of the two kinds of holes and provide estimates of their apparent effective masses.