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This article was originally published as: Fisher, TA, Simmonds, PE, Skolnick, MS, Martin, AD & Smith, RS, Fermi-energy edge singularity and excitonic enhancement associated with the second subband in asymmetric modulation-doped quantum wells, Physical Review B, 1993, 48(19), 14253-14263. Copyright 1993 American Physical Society. The original journal can be found here.


A study of the Fermi-energy edge singularity (FEES) in the second (n=2) subband of asymmetric modulation-doped (AlGa)As-(InGa)As-GaAs quantum wells (AMDQW’s) is reported. In one of the AMDQW’s a Schottky gate is employed to vary the electron density in the n=2 subband (ns,2) from 0 to 1×1011 cm-2. Temperature-dependent photoluminescence excitation (PLE) measurements clearly show that the n=2 PLE feature has FEES character for ns,2≳0.4×1011 cm-2. In contrast to PLE, photoluminescence (PL) intensity is not a true measure of oscillator strength, since PL intensity can be affected by competing recombination pathways. Temperature-dependent PL measurements have been performed on two types of AMDQW. One type has ns,2∼0, with the Fermi energy close to the n=2 subband energy. The other type has ns,2=1×1011 cm-2 and a FEES associated with n=2 observed in PLE. We demonstrate that the very similar broadening and reduction in peak height of the n=2 PL peak with temperature for the two types of samples can be accounted for in terms of spreading of the electron or exciton populations near the n=2 subband edge. Therefore, we conclude that temperature-dependent PL does not provide unequivocal evidence for a many-body enhancement of the n=2 PL transition, in contrast to that reported by Chen et al. [Phys. Rev. Lett. 64, 2434 (1990)].

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