Magneto-optics of two-dimensional electron gases modified by strong Coulomb interactions in ZnSe quantum wells

The optical properties of two-dimensional electron gases in $\mathrm{Zn}\mathrm{Se}∕(\mathrm{Zn},\mathrm{Be})\mathrm{Se}$ and $\mathrm{Zn}\mathrm{Se}∕(\mathrm{Zn},\mathrm{Be},\mathrm{Mg})\mathrm{Se}$ modulation-doped quantum wells with electron densities up to $1.4\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ were studied by photoluminescence, photoluminescence excitation, and reflectivity in a temperature range between 1.6 and $70\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and in external magnetic fields up to $48\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. In these structures, the Fermi energy of the two-dimensional electron gas falls in the range between the trion binding energy and the exciton binding energy. Optical spectra in this regime are shown to be strongly influenced by the Coulomb interaction between electrons and photoexcited holes. In high magnetic fields, when the filling factor of the two-dimensional electron gas becomes smaller than 2, a change from Landau-level-like spectra to exciton-like spectra occurs. We attempt to provide a phenomenological description of the evolution of optical spectra for quantum wells with strong Coulomb interactions.