Fermi-edge singularities in Be δ-doped two-dimensional electron gases

In a two-dimensional electron gas both photoluminescence (PL) and photoluminescence excitation (PLE) spectra have been studied. An electron gas with both high density and high mobility has been obtained by remote modulation doping with X-electrons of a GaAs single quantum well. A number of almost identical samples have been studied, where in one of them a low density Be delta-doped layer is placed in the center of the well, while maintaining the mobility at a high value. The partial localization of photogenerated holes gives rise to the presence of band-to-acceptor transitions, visible in both PL and PLE spectra. Optical singularities at the Fermi edge (FES) have been observed in these spectra, and have been compared to the sample without Be doping. In PLE strong FES have been observed for both localized and free valence band holes, contrary to the present understanding of the FES origin.