EFFECT OF FINAL-STATES ON ELECTRON-TUNNELING IN COUPLED QUANTUM-WELL STRUCTURES

We have studied the effect of final states, the ground state and the first excited state, on electron tunnelling in asymmetric double QW structures. The tunnelling transfer time reached its minimum under resonant conditions when the destination was the first excited state. When the final state is the ground state of the adjacent well, however, it is found that the tunnelling transfer time reaches its minimum not under on-resonant but rather under off-resonant conditions. The energy difference between the initial and the final states at the transfer minimum is estimated to be around 17 meV, which eliminates LO phonon-assisted tunnelling as the mechanism. The actual transfer mechanism is most likely related to the interface roughness when the destination is the ground state.