On the mechanisms of energy transfer between quantum well and quantum dashes

We investigate energy transfer mechanisms from a quantum well (QW) to quantum dashes (QDashes) separated by a few nanometer thick barrier in InAs/InGaAs/InGaAlAs/InP material system. We show that at sufficiently low temperatures excitons, which are non-resonantly photogenerated in the QW and then transferred to the ground state via phonon relaxation, can be retrieved by QDashes. The excess of the transferred energy, defined by the energy difference between the QW and QDash exciton states, can be dissipated via interaction with LO phonons if the respective energy matching is satisfied. This kind of exciton injection from QW to QDashes is a process insensitive to the energy level structure of the individual exciton components, i.e., electrons and holes. It is shown that within the single particle picture, the electron energy in QDashes is higher by more than 50 meV compared to the corresponding QW energy, which prevents the electron transfer from quantum well to the dashes. We show experimentally that despite this unfavorable energy difference for single carriers whole QW excitons are efficiently transferred to QDashes and recombine there radiatively. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4743002]