Direct and spatially indirect excitons in GaAs/AlGaAs superlattices in strong magnetic fields |
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Authors: | A I Tartakovskii V B Timofeev V G Lysenko D Birkedal J Hvam |
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Institution: | (1) Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia;(2) Institute of Microelectronics and High-Purity Materials, 142432 Chernogolovka, Russia;(3) Microelectronics Center, The Technical University of Denmark, DK 2800 Lyngby, Denmark |
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Abstract: | Luminescence and luminescence excitation spectra are used to study the energy spectrum and binding energies of direct and
spatially indirect excitons in GaAs/AlaAs superlattices, with different widths of the electron and hole minibands, located
in a high magnetic field perpendicular to the heterolayers. It is found that the ground state of the indirect excitons formed
by electrons and holes and spatially separated between neighboring quantum wells lies between the ls ground state of the direct excitons and the continuum threshold for dissociated exciton states in the minibands. Indirect
excitons in superlattices have a significant oscillator strength when the binding energy of the exciton exceeds the order
of the width of the resulting miniband. The behavior of the binding energy of direct and indirect heavy hole excitons during
changes in the tunneling coupling between the quantum wells is established. It is shown that a strong magnetic field, which
intensifies the Coulomb interaction between the electron and hole in an exciton, weakens the bond in a system of symmetrically
bound quantum wells. The spatially indirect excitons studied here are analogous to first order Wannier-Stark localized excitons
in superlattices with inclined bands (when an electrical bias is applied), but in the present case the localization is of
purely Coulomb origin.
Zh. éksp. Teor. Fiz. 112, 1106–1118 (September 1997) |
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