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

Abstract

The optical properties of two-dimensional electron gases in ZnSe/(Zn,Be)Se and ZnSe/(Zn,Be,Mg)Se modulation-doped quantum wells with electron densities up to 1.4 × 10 12 cm −2were studied by photoluminescence, photoluminescence excitation and reflectivity in a temperature range between 1.6 and 70 K and in external magnetic fields up to 48 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 two, 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.

Trion states in a dense 2DEG

“…In zero magnetic fields a broad PL band, called in some publications a Fermi Edge Singularity [3], emerges in the spectral range of exciton and trion lines. In non-zero magnetic field these broad bands split into a series of relatively narrow lines that shift linearly towards higher energies and also to low energies.…”

Magneto‐optics of modulation doped quantum wells based on II–VI semiconductor compounds

“…However, despite the visual similarity in the shape of PL band, this simple interpretation is insufficient to describe the optical spectra in the intermediate concentration regime where E T B < ε F < E X B . Coulomb interactions and excitonic effects are of great importance in this regime [8].…”

“…In the regime of a moderate 2DEG density were the Fermi energy of the 2DEG falls in the range between the trion and exciton binding energies (E T B < ε F < E X B ), the optical spectra can be phenomenologically described in terms of excitonic effects accompanied with the many-body excitations in the 2DEG [8].…”

Second hidden triplet-singlet crossover of charged excitons inn-doped (Cd,Mn)Te/(Cd,Mg)Te in ultra-high magnetic fields

“…[24][25][26][27][28][29][30][31][32] In this intermediate region of the electron density, the PL spectra in low magnetic fields ͑ Ͼ 2͒ show the Landau-level-like behavior 26,29 while in high magnetic fields ͑ Ͻ 1͒ the PL turns out to be a simple excitonic or charged excitonlike behavior. 26 When the filling factor becomes that between 1 and 2, the PL shows spectral features of both Landau-type and excitonic transitions. Therefore, in the magnetic field regimes of Ͼ 1, the PL spectra in intermediate electron density are more complicated than those in both cases of low and high electron-density regions.…”