Wannier-Stark effect in strongly coupled three quantum well structures andsuperlattices

The Wannier-Stark effect has been investigated in strongly coupled three qu antum well structures and 23.5 period superlattices consisting of 25 Angstr om wide GaAs wells separated by Al0.25Ga0.75As barriers of the same width. A blue shift associated with the Wannier-Stark localization of heavy holes states is observed for the first time, followed by a second blue shift at h igher electric fields due to the electron localization. This is contrary to the widely reported single blue shift of the order of (Delta e+Delta hh)/2 , where Delta e and Delta hh are the electron and heavy hole miniband width s respectively, produced by Wannier-Stark localization in superlattices.