Dynamics of Electric Field Domains in Superlattices

Abstract

A discrete drift model of resonant tunneling transport in weakly-coupled GaAs quantum-well structures under laser illumination is introduced and analyzed. Results include explanations (via formation of electric field domains) of the oscillatory shape of the I-V diagram leading to multistability and hysteresis between stationary electric-field profiles for both doped and undoped superlattices under strong laser illumination. Moreover, the dynamics of electric-field domains and domain walls in our model account for damped and undamped time-dependent oscillations of the current in a dc voltage bias situation, with the laser photoexcitation acting as a damping factor. Our results agree with time-resolved photoluminescence and photocurrent experiments. An asymptotic analysis of the continuum limit of our discrete model shows that these current oscillations are due to the formation, motion, annihilation and regeneration of negatively charged domain walls on the superlattice. The situation is reminiscent of the classical Gunn-effect oscillations in bulk semiconductors due to dipole-domain dynamics, and in fact our present asymptotic analysis is an extension and adaptation of previous work of ours on the Gunn effect.