No abstract

We study the electronic and optical properties of laterally coupled InGaAs/GaAs quantum dot molecules under lateral electric fields. We find that the electrons perceive the double-dot structure as a compound single object and tunnel through a basin connecting the dots from underneath. The holes discern two well-separated dots and are unable to tunnel. Through a combination of predictive atomistic modeling, detailed morphology studies, and single-object microphotoluminescence measurements, we show that this peculiar confinement results in an unusual heterogeneous behavior of electrons and holes with profound consequences on optical properties. We find a qualitatively different signal in optical-absorption, emission under resonant, and emission under nonresonant excitations. We explain this behavior by invoking the carriers' dynamics following light absorption.

We report on the charge carrier dynamics in single lateral quantum dot molecules and the effect of an applied electric field on the molecular states. Controllable electron tunneling manifests itself in a deviation from the typical excitonic decay behavior which is strongly influenced by the tuning electric field and inter-molecular Coulomb energies. A rate equation model is developed to gain more insight into the charge transfer and tunneling mechanisms. Non-resonant (phonon-mediated) electron tunneling which changes the molecular exciton character from direct to indirect, and vice versa, is found to be the dominant tunable decay mechanism of excitons besides radiative recombination.The charge carrier configuration and dynamics in coupled quantum dot (QD) systems are the essential properties that need to be understood in order to gain the ability to coherently manipulate the coupling in the system using external electric, magnetic or light fields. This degree of control over the QD system represents an essential step toward the realization of quantum gates. Over the past number of years, optically addressable self-assembled semiconductor single QDs have been presented as sources for triggered single-photons and polarization entangled photon pairs [1,2,3,4,5], and first quantum gates have been demonstrated [6,7]. Such QDs can be assembled to larger molecular structures by vertically stacking them along the growth direction [8,9,10,11,12,13,14] and laterally arranging them [15,16,17]. A recent demonstration on a vertical QD molecule (QDM) has shown conditional quantum dynamics with one QD state being controlled via the other one [18]. The static properties of different types of QDMs, such as their coupling mechanisms and electronic structure, as well as, emitted photon characteristics have been extensively experimentally studied and theoretically described [10, 11, 12, 19, 20, 21]. A detailed dynamical analysis of the coupling in lateral QDMs using timeresolved spectroscopic methods, however, has not yet been done. As previously reported in Refs. [17,20,21], the dominant coupling mechanism in lateral double-dots is electronic tunneling, which strongly depends on the charge carriers' effective masses, the excitonic binding energies and the potential landscape. It is therefore of particular interest to study the dependence of the tunnel dynamics on these parameters, especially considering the long-term objective of gaining the ability to control them in a deterministic way. In this report we introduce our results obtained for experimental and theoretical examinations of the charge carrier and exciton dynamics * now at: The Cavendish Laboratory, University of Cambridge, J. J. Thomson Ave., Cambridge, CB3 0HE, UK of laterally coupled QDs which highlight the significant difference to single-dots and the important impact of a manipulating electric field.Due to their specific growth mode [16] the QDMs under investigation are all aligned along the same crystallographic axis [110], as displayed in the atomic force microgra...

No abstract