A new mechanism for negative differential conductivity in superlattices

Electrons in a superlattice at high fields are suitably described in terms of localized states related to the potential wells. Conduction is dominated by transitions between adjacent wells if the potential drop over a superlattice period exceeds the width of the lowest miniband. It is shown that the probability of these transitions, and consequently the current as well, decrease with increasing field. This effect originates from decreasing overlap between electron states of neighbouring wells, and it is found for the interaction with acoustic phonons and with impurities as well.