Behavior of the Fermi-edge singularity in the photoluminescence spectra of a high-density two-dimensional electron gas

Fundamentally different behavior of the Fermi-edge singularity (FES) in photoluminescence of heavily doped pseudomorphic modulation-doped ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}}_y{\mathrm{Ga}}_{1-y}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ heterostructures is observed. The noteworthy features are: (i) the FES enhancement from $E_F$ of $n=1\mathrm{}$ electronic subband is observed under condition of the $n=2\mathrm{}$ subband population, (ii) the heavy-hole localization energy is directly observed in the FES development, (iii) the magnitude of the FES increases with increasing temperature at low temperatures, and (iv) the FES is a nonmonotonic function of the excitation density. A qualitative analysis is performed in terms of heavy-hole localization by potential fluctuations in the ${\mathrm{In}}_y{\mathrm{Ga}}_{1-y}\mathrm{As}$ quantum well.