Local modulation of the quantum-well quasicontinuum states using charged-carrier transfer induced by intersubband transitions

By generating a local electric field across an asymmetrical coupled quantum-well structure and using resonant Raman spectroscopy as a probe, we were able to resolve two classes of continuum electronic states of energies close to the barrier height. The first class is related to a continuum resonant state that is located near the edge of the barrier and is extended across the barrier region but not across the coupled quantum wells. The second class of continuum states is related to a quasibound resonant state that is localized above the quantum wells. Therefore, a local electric field across the coupled quantum wells modifies the energy spectrum of the localized resonant state while keeping the delocalized resonance unaffected. In our experiment the local electric field was generated by intersubband photoexcitation of carriers from one quantum well to the other. We observed a redshift of the quasibound resonant state due to the intersubband photoexcitation.