Lateral quantum coupling between two self-assembled (In,Ga)As quantum dots has been observed. Photon statistics measurements between the various excitonic and biexcitonic transitions of these lateral quantum dot molecules display strong antibunching confirming the presence of coupling. Furthermore, we observe an anomalous exciton Stark shift with respect to static electric field. A simple model indicates that the lateral coupling is due to electron tunneling between the dots when the ground states are in resonance. The electron probability can then be shifted to either dot and the system can be used to create a wavelength-tunable single-photon emitter by simply applying a voltage.

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We experimentally demonstrate Cooper pairs' drastic enhancement of the band-to-band radiative recombination rate in a semiconductor. Electron Cooper pairs injected from a superconducting electrode into an active layer by the proximity effect recombine with holes injected from a p-type electrode. The recombination of a Cooper pair with p-type carriers dramatically increases the photon generation probability of a light-emitting diode in the optical-fiber communication band. The measured radiative decay time rapidly decreases with decreasing temperature below the superconducting transition temperature of the niobium electrodes. Our results indicate the possibility to open up new interdisciplinary fields between superconductivity and optoelectronics. DOI: 10.1103/PhysRevLett.107.157403 PACS numbers: 78.60.Fi, 74.25.Gz, 78.66.Fd, 85.60.Jb Recent discoveries of new superconductors [1,2] boosted up the research fields with new experimental as well as theoretical possibilities. From a scientific viewpoint one great advantage of superconductivity is its long coherence time which is the most important feature for quantum information processing [3]. The combined system consisting of a coherent photon field and a superconducting (SC) condensate would be a promising candidate for realizing the quantum operation in solid state devices [4][5][6][7][8]. The Cooper pairs are preserved during these operations with photon energies smaller than the energy gap of superconductivity (on the order of meV). On the other hand, when photon energies become larger than the superconductivity gap, the absorption of high-energy photons only results in the destruction of Cooper pairs. This fact enables the application of superconductors as high-speed singlephoton detectors [9]. It is still unexplored what will take place with the counter process of photon emission from Cooper-pair states in this higher photon energy range.In this Letter, we demonstrate that electron Cooper pairs injected into a semiconductor by the proximity effect [10,11] can be highly involved in the interband transition and accelerate the photon generation processes. We measure the radiative recombination rate as a function of temperature across the SC transition temperature, T C . The results demonstrate drastic enhancement of the radiative recombination rate below T C . The temperature dependence of the radiative recombination rate can be explained by a theoretical model. Our new finding corresponds to experimental demonstration of the Cooper pair's gigantic oscillator strength [12].The light-emitting diode (LED) epitaxial layers were grown on a p-type (001) InP substrate by metalorganic vapor-phase epitaxy. The layers consist of a 500 nm thick p þ À InP buffer layer (Zn doping $1 Â 10 17 cm À3 ), a 30 nm thick n þ À In 0:53 Ga 0:47 As active layer (Si doping $5 Â 10 18 cm À3 ) lattice matched to InP, and a 10 nm thick n þ À In 0:7 Ga 0:3 As Ohmic contact layer (Si doping $5 Â 10 18 cm À3 ). Outside of the contact layer, we attached 20 m wide and 80 nm thick niobium (N...

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...

Correlations between the morphology and emission properties of trench defects in InGaN/GaN quantum wells J. Appl. Phys. 113, 073505 (2013) Optical characterization of free electron concentration in heteroepitaxial InN layers using Fourier transform infrared spectroscopy and a 2×2 transfer-matrix algebra J. Appl. Phys. 113, 073502 (2013) Influence of structural anisotropy to anisotropic electron mobility in a-plane InN Appl. Phys. Lett. 102, 061904 (2013) Sub-250nm light emission and optical gain in AlGaN materials J. Appl. Phys. 113, 013106 (2013) Effects of pumping on propagation velocities of confined exciton polaritons in GaAs/AlxGa1−xAs double heterostructure thin films under resonant and non-resonant probe conditions J. Appl. Phys. 113, 013514 (2013) Additional information on J. Appl. Phys.

Single lateral InGaAs quantum dot molecules have been embedded in a planar micro-cavity in order to increase the luminescence extraction efficiency. Using a combination of metal-organic vapor phase and molecular beam epitaxy samples could be produced that exhibit a 30 times enhanced single-photon emission rate. We also show that the single-photon emission is fully switchable between two different molecular excitonic recombination energies by applying a lateral electric field. Furthermore, the presence of a polarization fine-structure splitting of the molecular neutral excitonic states is reported which leads to two polarization-split classically correlated biexcitonexciton cascades. The fine-structure splitting is found to be on the order of 10 µeV.

We investigate the photoluminescence temperature dependence of individual InAs/InGaAlAs quantum dots emitting in the optical telecommunication bands. The high-density dots are grown on InP substrates and the selection of a smaller dot number is done by the processing of suitable nanometer-sized mesas. Using ensembles of only a few dots inside such mesas, their temperature stability, inter-dot charge transfer, as well as carrier capture and escape mechanisms out of the dots are investigated systematically. This includes the discussion of the dot ensemble and individual dots. Among the single-dot properties, we investigate the transition of emission lines from zero-phonon line to acoustic phonon sideband-dominated line shape with temperature. Moreover, the presence of single recombination lines up to temperatures of about 150 K is demonstrated.