Ultrafast Studies of Resonant and Non-Resonant Electron and Hole Tunneling in Quantum Well Structures

Abstract

Quantum mechanical phenomenon of tunneling is of fundamental interest and strongly influences high speed devices based on perpendicular transport of carriers in semiconductor microstructures. Ultrafast lasers provide ideal means for studying tunneling in such structures. We review in this talk our recent investigations of resonant and non-resonant tunneling of electrons and holes in asymmetric double quantum well structures (a-DQWS) using ultrafast luminescence spectroscopy. These investigations have directly determined various tunneling rates and have provided new insights into tunneling in microstructures. For the non-resonant case, we have determined the dependence of tunneling rate on the barrier thickness and the energy separation between the two electronic levels. We have shown that impurity-assisted tunneling rate is small and optical- phonon-assisted tunneling dominates when the energy separation allows this process. For the case of resonant tunneling, we have shown that tunneling rates are considerably smaller than expected because of destruction of coherence by relaxation and collisions and have developed a unified picture of tunneling in the presence of relaxation and collisions.