Final-state excitations in the photoluminescence spectra of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-InP quantum wells at low and high carrier density

Longitudinal-optic (LO) phonon and Fermi-sea shake-up excitations are studied in the magneto-optical spectra of ${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-InP quantum wells. The final-state excitations are observed as low-energy satellites in photoluminescence spectra in magnetic fields up to 20 T. Clear resonant interactions between the LO-phonon and shake-up satellites are observed. In the low-density sample (${\mathit{n}}_{\mathit{s}}$=1.15×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$) studied, interaction between the shake-up satellite, corresponding to promotion of an electron from the ${\mathit{N}}_{\mathit{e}}$=0 to the ${\mathit{N}}_{\mathit{e}}$=1 Landau level, and the LO-phonon satellite of the ${\mathit{N}}_{\mathit{e}}$=0 Landau-level transition, is observed. The other two samples investigated have high carrier density of 9.2×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$; one sample has strong disorder and strong hole localization and the other weak disorder and weak hole localization. The sample with strong hole localization exhibits a Fermi-energy-edge singularity in its photoluminescence (PL) spectrum at zero magnetic field, and has strong phonon and shake-up satellites. The other high-density sample has a very weak PL signal at the Fermi energy and phonon and shake-up satellites at high field at least an order of magnitude weaker than in the sample with strong hole localization. This behavior arises since the strength of the Fermi edge singularity and the coupling to the LO phonon and shake-up excitations both depend on the degree of hole localization in the system.