DYNAMICS OF ELECTRIC-FIELD DOMAINS AND CHAOS IN SEMICONDUCTOR SUPERLATTICES

A discrete drift model of sequential resonant tunneling in weakly-coup led doped or undoped GaAs/AlAs superlattices (SL) under d.c. or d.c. a.c. voltage bias and laser illumination is analyzed. In agreement wi th experiments our model shows an oscillatory I-V diagram for large en ough values of the doping and/or laser illumination, multistability an d hysteresis between stationary solutions and self-sustained time depe ndent oscillations of the current. Numerical and asymptotic analyses o f the model show that these current oscillations are due to the format ion, motion, annihilation and regeneration of negatively charged domai n walls on the SL. For appropriate d.c. + a.c. voltage bias, chaotic c urrent oscillations with loss of spatial coherence of the electric fie ld will appear due to random nucleation of domains in the SL.