Spatiotemporal dynamics in optically excited quantum wire-dot systems: Capture, escape, and wave-front dynamics

Reiter D, Glanemann M, Axt VM, Kuhn T

Abstract

Transitions of optically excited carriers between delocalized states in a quantum wire and localized states in a quantum dot are studied on a quantum kinetic level. These transitions are mediated by the emission or absorption of longitudinal optical phonons. Three different excitation scenarios are considered: The capture of a traveling wave packet results in occupations of the bound states and, under suitable conditions, in coherent superpositions. Both occupations and coherences decay due to thermal escape processes resulting from the absorption of phonons. A spatially homogeneous excitation in the quantum wire below the threshold for optical phonon emission leads to capture processes associated with the buildup of a wave front in the carrier density between regions which are already influenced by the capture and regions where this influence is not yet present. A selective excitation of the quantum dot exciton is at elevated temperatures followed by thermal escape processes with a subsequent spreading of the carriers in the quantum wire. We find that for a physically meaningful description of the spatiotemporal dynamics a consistent treatment of both diagonal and off-diagonal density matrix elements is essential in all three scenarios.