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. We compare different superlattice structures with high and with low barriers to alternatively investigate the effects of resonant interminiband tunneling and a strong Zener coupling to continuum states. The associated electrical 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 by time-resolved experiments. [References: 8]
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