Kinetics of intersubband optical excitation and photoinduced electron transfer in an asymmetric double quantum well

Optical excitation of electrons in an asymmetric double quantum well is theoretically examined. The well is biased to align the excited levels and permit resonant electron tunneling. Emphasis is made on the photoinduced transfer of electrons counter to the bias electric-field force. Systems with a weak polarization relaxation (dephasing) are studied with use of the conventional Schrödinger-equation technique. A density-matrix approach is developed to describe optical excitations in the presence of an arbitrary dephasing. Quantum beats, which follow a short-pulse excitation of the double well, are shown to depend crucially on the dephasing. The excitation profiles obtained for cases of different dephasing reveal the full range of tunneling coupling between the wells from completely coherent to incoherent (stepwise).