  Temperature dependence and recombination behavior of trapped charge carriers
in ZnCdSe/ZnSe multiple quantum wells are investigated employing surface
acoustic waves. These weakly perturb the carrier system, but remain highly
sensitive even at small conductivities. Using this non-invasive probe we are
able to detect persistent photoconductivity minutes after optical excitation.
Measurement of exciting photon energies, the temperature dependence and ability
to quench the conductivity with energies lower than the bandgap, support the
notion of spatial separation of electrons and holes in the wells, due to random
local potential fluctuations possibly induced by compositional fluctuations.
