EXCITON SPECTRA OF SEMICONDUCTOR SUPERLATTICES IN A PARALLEL MAGNETIC-FIELD

Low-temperature photoluminescence and photoluminescence excitation spe ctra of GaAs/AlGaAs semiconductor superlattices having different poten tial barrier widths (b = 20, 30, 50, and 200 Angstrom), i.e., degrees of tunnel coupling between quantum wells, are studied in magnetic fiel ds up to 5 T oriented parallel and perpendicular to the layers of the structure. The changes in the qualitative character of the photolumine scence excitation spectra observed in a parallel magnetic field with i ncreasing tunnel transparency of the barrier correspond to a transitio n from a quasi-two-dimensional to a quasi-three-dimensional electronic spectrum as a miniband develops in the superlattice. In the photolumi nescence excitation spectra of the superlattice with b = 50 Angstrom, as the parallel magnetic field is increased, a new line appears in the violet wing of the spatially indirect exciton excitation line, which is absent in a perpendicular field. A similar line was also observed t o arise in the photoluminescence spectra. It is shown that the indirec t exciton luminescence line can be suppressed by both parallel and per pendicular magnetic fields. (C) 1998 American Institute of Physics.