Domain-wall kinetics and tunneling-induced instabilities in superlattices

We report on time-resolved studies of electric-field domains in weakly coupled GaAs quantum-well structures. Photoluminescence and photocurrent experiments probe the motion of charged domain walls triggered by steplike changes in the illumination. Results reveal complex oscillations with frequencies in the range 4--8 MHz. These findings are discussed in terms of a discrete drift model relying on negative-differential conductance due to resonant tunneling. Calculations give a global phase diagram and time behavior consistent with experiments.