We have performed a detailed study of low-temperature photoluminescence (PL) from a pair of modulation-doped GaAs/Al${}_x$Ga${}_{1-x}$As multiple-quantum-well samples finding weak Fermi-edge singularities (FES’s) associated with both heavy-hole and light-hole subbands. In contrast to previous 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 to be comparable to that in systems with localized holes. The enhancement of the PL spectrum is significantly stronger than that of the absorption spectra from the same samples. Comparison with previously published data suggests that this asymmetry may be a general property of two-dimensional electron systems.

• Received 16 January 1997

DOI:https://doi.org/10.1103/PhysRevB.56.3937