Electron decay from coupled quantum wells to a continuum: Observation of relaxation-induced slow down

Using time-resolved optical spectroscopy we study the decay of electrons from symmetric coupled quantum wells to a continuum through a potential barrier. We find a nonmonotonic dependence of the decay rate on the thickness of the barrier. At the limit of a thin barrier the decay rate decreases with decreasing barrier thickness and the energy splitting between the electron levels disappears. We show that this behavior is general for systems where resonant tunneling is coupled to a relaxation channel.