Transport of a wave packet through nanostructures: Quantum kinetics of carrier capture processes

Abstract

Capture processes of an electronic wave packet traveling in a quantum wire into localized states of an embedded quantum dot by means of phonon emission are studied in a quantum kinetic approach. It turns out that due to the ultrashort length and time scales involved the capture processes exhibit a variety of quantum kinetic features which cannot be described by a simple semiclassical capture rate. We find in general a nonmonotonic rise of the occupation of bound states even at low temperatures where no phonon absorption is possible. This is related to the finite collision duration and the presence of coherent superpositions between initial and final states in the scattering process giving rise to phonon Rabi oscillations between free and trapped states. In the case of more than one bound state in the dot typically a linear combination of these bound states is populated, which leads to a nontrivial dynamics of the trapped carrier density. For potential profiles with large reflection probability it turns out that also the transmission and reflection behavior is modified by the capture process. Finally the theory is applied to a two-band model including optical excitation and excitonic effects. For the scenarios studied in the paper these phenomena lead to some quantitative modifications but they do not change the characteristic quantum features of the capture dynamics.