  The magnetoresistance of the MBE-grown GaAs/AlGaAs superlattice with Si-doped
barriers has been measured in tilted magnetic fields in the as-grown state, and
after brief illumination by a red-light diode at low temperature, T is
approximately 0.3 K. A remarkable illumination-induced modification of
magnetoresistance curves has been observed, which indicates a significant
change of the superlattice Fermi surface topology. Analysis of
magnetoresistance data in terms of the tight-binding model reveals that not
only electron concentration and mobility have been increased by illumination,
but also the coupling among 2D electron layers in neighboring quantum wells has
been reduced.
