FERMI-EDGE SINGULARITIES IN PHOTOLUMINESCENCE FROM MODULATION-DOPED GAAS QUANTUM-WELLS

We have performed a detailed study of low-temperature photoluminescenc e (PL) from a pair of modulation-doped GaAs/AlxGa1-xAs multiple-quantu m-well samples finding weak Fermi-edge singularities (FES's) associate d with both heavy-hole and light-hole subbands. In contrast to previou s experiments it appears that the presence of the FES's is not due to hole localization or the proximity of a second electronic subband. The many body enhancement above the single particle background is found t o be comparable to that in systems with localized holes. The enhanceme nt of the PL spectrum is significantly stronger than that of the absor ption spectra from the same samples. Comparison with previously publis hed data suggests that this asymmetry may be a general property of two -dimensional electron systems.