Polarization fine structure and enhanced single-photon emission of self-assembled lateral InGaAs quantum dot molecules embedded in a planar microcavity

Hermannstädter, Claus; Witzany, M.; Beirne, G. J.; Schulz, Wolfgang-Michael; Eichfelder, M.; Roßbach, R.; Jetter, Michael; Wang, L.; Rastelli, Armando; Schmidt, Oliver G.; Michler, Peter

doi:10.1063/1.3117234

Cited by 12 publications

(14 citation statements)

References 36 publications

(50 reference statements)

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“…A detailed description of the structure under investigation is given in Ref. [22] including the demonstration of quantum coupling via photon cross-correlation spectroscopy. For the measurements that are presented here, the sample was mounted in a low temperature (5 K) micro-PL setup that enables the observation of single molecules within a focus diameter of about 1 µm.…”

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Influence of the charge carrier tunneling processes on the recombination dynamics in single lateral quantum dot molecules

et al. 2010

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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...

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Influence of the charge carrier tunneling processes on the recombination dynamics in single lateral quantum dot molecules

et al. 2010

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“…21, we previously reported on the biexciton-exciton cascades in lateral QDMs. 22 In that work, a FSS on the order of 10 leV was measured and two uncharged radiative cascades could be identified. However, the polarization anisotropy, i.e., the polarization degree of the QDM PL has not been investigated until now and is discussed below.…”

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“…The total QDM active layer is embedded inside a planar lambda-cavity with 20 bottom pairs and one top pair of AlAs/AlGaAs distributed Bragg reflectors in order to obtain a higher photoluminescence (PL) extraction at the typical emission energy of around 1.35 eV. 22 The reliable and repeatable alignment of all QDMs along the ½1 10 direction allows for the application of electric fields along a controlled direction with respect to the QDM coupling axis. The static electric fields are created by voltage control of parallel metal electrodes that are deposited on top of the sample with spacings of 5 to 20 lm between them.…”

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“…The related crosscorrelations between different QDM PL lines are presented elsewhere. 13,22,29 B. Polarization analysis of the dot molecule luminescence…”

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confidence: 99%

“…15,16 The polarization properties of QDs that are used as entangled photon pair sources, such as the exciton fine structure (FS) and its tuning, are very important and have been widely discussed, both for single InGaAs/GaAs QDs [17][18][19][20] and QD molecules (QDMs). 21,22 Tuning the FS splitting (FSS) of the neutral exciton state to values on the order of its natural linewidth is a promising approach to use the respective radiative biexciton-exciton cascaded emission process to produce polarization entangled photon pairs. [3][4][5] Strain-induced anisotropic exchange interaction (AEI) and valence-band mixing (VBM) might have an impact on the exciton FS, even for highly symmetric single QDs and QDMs, and are recently also discussed as possible sources for polarization anisotropy.…”

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Polarization anisotropic luminescence of tunable single lateral quantum dot molecules

Hermannstädter

Witzany

Heldmaier

et al. 2012

Journal of Applied Physics

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Identification of visible emission from ZnO quantum dots: Excitation-dependence and size-dependence J. Appl. Phys. 111, 083521 (2012) Chromium-oxide enhancement of photo-oxidation of CdSe/ZnS quantum dot solids J. Appl. Phys. 111, 084308 (2012) Internal structure of tunable ternary CdSexS1−x quantum dots unraveled by x-ray absorption spectroscopy Appl. Phys. Lett. 100, 163113 (2012) Formation of coupled three-dimensional GeSi quantum dot crystals Appl. Phys. Lett. 100, 153113 (2012) Additional information on J. Appl. Phys. We investigate the photoluminescence polarization anisotropy of self-assembled individual lateral InGaAs/GaAs quantum dot molecules. In contrast to similarly grown single quantum dots, the dot molecules exhibit a remarkable degree of linear polarization, which remains almost unchanged when a lateral electric field is applied to tune the exciton wave function and, thus, the luminescence spectral properties. We discuss the nature of this polarization anisotropy and suggest possible causes based on the system's symmetry and heterostructure alloy composition.

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Transient absorption spectroscopy of a single lateral InGaAs quantum dot molecule

Wolpert

Wang

Rastelli

et al. 2012

Physica Status Solidi (b)

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Lateral quantum dot molecules promise a scalable approach to quantum registers. The individual neutral exciton states can be controlled by a lateral bias voltage. In this way radiative emission of localized excitons can be switched between the two quantum dots in the molecule. Here, we report on coherent absorption spectroscopy of a single quantum dot molecule. By transient reflection spectroscopy we demonstrate that not only the emission but also the absorption switches from one dot to the other when varying the applied electric field. This result is consistent with Rabi flopping showing a radically suppressed dipole moment for the non-emitting exciton transition ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Self-assembled quantum dot molecules (QDMs) were studied extensively in recent years due to their potential application as basic building blocks in quantum computation [1] and as tunable singlephoton sources [2]. Individual neighboring quantum dots are coupled in a controlled way by shifting their excitonic states with gate electrodes via the Stark effect. Vertically arranged QDMs [3-5] make the application of individual electrodes technologically demanding and the upscaling to larger quantum registers problematic. An attractive alternative are laterally coupled quantum dot molecules [6]. Their planar geometry allows for coupling in two directions and makes upscaling of the system conceptually straight-forward. Connections between individual QDMs can be realized by plasmonic wires [7] and waveguides [8].While a signature of the coupling between the quantum dots in the QDM is observable in steady-state photoluminescence, an application of the QDM in the field of quantum computing requires ultrafast spectroscopy [9]. All operations on the quantum register need to be completed within the coherence time of the quantum dot which is typically in the order of some tens to hundreds of picoseconds [10,11]. In this article we present ultrafast transient reflection spectroscopy [12] on a single InGaAs quantum dot molecule.

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Polarization fine structure and enhanced single-photon emission of self-assembled lateral InGaAs quantum dot molecules embedded in a planar microcavity

Cited by 12 publications

References 36 publications

Influence of the charge carrier tunneling processes on the recombination dynamics in single lateral quantum dot molecules

Influence of the charge carrier tunneling processes on the recombination dynamics in single lateral quantum dot molecules

Polarization anisotropic luminescence of tunable single lateral quantum dot molecules

Transient absorption spectroscopy of a single lateral InGaAs quantum dot molecule

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