DIRECT AND SPATIALLY INDIRECT EXCITONS IN GAAS ALGAAS SUPERLATTICES IN STRONG MAGNETIC-FIELDS/

Luminescence and luminescence excitation spectra are used to study the energy spectrum and binding energies of direct and spatially indirect excitons in GaAs/AlGaAs superlattices, with different widths of the e lectron and hole minibands, located in a high magnetic field perpendic ular to the heterolayers. It is found that the ground state of the ind irect excitons formed by electrons and holes and spatially separated b etween neighboring quantum wells lies between the Is ground state of t he direct excitons and the continuum threshold for dissociated exciton states in the minibands. Indirect excitons in superlattices have a si gnificant oscillator strength when the binding energy of the exciton e xceeds the order of the width of the resulting miniband. The behavior of the binding energy of direct and indirect heavy hole excitons durin g changes in the tunneling coupling between the quantum wells is estab lished. It is shown that a strong magnetic field, which intensifies th e Coulomb interaction between the electron and hole in an exciton, wea kens the bond in a system of symmetrically bound quantum wells. The sp atially indirect excitons studied here are analogous to first order Wa nnier-Stark localized excitons in superlattices with inclined bands (w hen an electrical bias is applied), but in the present case the locali zation is of purely Coulomb origin. (C) 1997 American Institute of Phy sics. [S1063-7761(97)02209-9].