Field-induced delocalization and Zener breakdown in semiconductor superlattices

We investigate the energy spectrum and the electron dynamics of a band in a semiconductor superlattice as a function of the electric field. Linear opt ical spectroscopy shows that, for high fields, the well-known localization of the Bloch states is followed by a field-induced delocalization, associat ed with Zener breakdown. Using time-resolved measurements, we observe Bloch oscillations in a regime where they are damped by Zener breakdown.