Field-induced delocalization and zener breakdown in semiconductor superlattices

We investigate the electronic structure in strongly coupled superlattices over a wide field range. It is shown that the Wannier-Stark localization is followed by a field-induced delocalization which is due to a strong Zener coupling to continuum states. The associated Zener breakdown is quantitatively shown in a detailed analysis of the absorption. A comprehensive theoretical model excellently describes the experimental results. Zener tunneling times are directly addressed with the help of time-resolved experiments.