EXTENDED STATES AND DYNAMICAL LOCALIZATION IN SEMICONDUCTOR SUPERLATTICES

We study the quantum dynamics of electronic wave packets in quantum-we ll based semiconductor superlattices subject to an applied electric fi eld. Using a high-accuracy numerical method, we analyze the dynamical behavior of electronic wave packets in periodic, random and random dim er superlattices. The spatial extent of electronic states is character ized by means of the time-dependent inverse participation ratio. We sh ow that the delocalized states recently found in random dimer superlat tices become spatially localized under the action of the applied field (dynamical localization) but wavepackets are much less localized than in purely random superlattices at moderate field. We conclude that th e resonant tunneling effects causing delocalization in dimer superlatt ices play an important role even in the presence of moderate electric field. (C) 1997 American Institute of Physics.