Stark localization and resonance-induced delocalization of electrons in GaAs/AlAs superlattices.

We have investigated p-i-n diode structures containing GaAs/AlAs superlattices with extremely thin (<1nm) barriers by photocurrent and resonant Raman spectroscopy. Stark localization of miniband states is observed at low electric fields. At high fields, we find a novel delocalization effect which is induced by the resonant coupling between different Stark ladders and strongly influences the absorption properties of the superlattice. Moreover, Stark ladders are very interesting systems for Raman spectroscopy since multiple resonance conditions can be realized for the Raman process by creating equidistant Stark ladder states in an electric field.