169 research outputs found

    Understanding Polarization Properties of InAs Quantum Dots by Atomistic Modeling of Growth Dynamics

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    A model for realistic InAs quantum dot composition profile is proposed and analyzed, consisting of a double region scheme with an In-rich internal core and an In-poor external shell, in order to mimic the atomic scale phenomena such as In-Ga intermixing and In segregation during the growth and overgrowth with GaAs. The parameters of the proposed model are derived by reproducing the experimentally measured polarization data. Further understanding is developed by analyzing the strain fields which suggests that the two-composition model indeed results in lower strain energies than the commonly applied uniform composition model.Comment: in press, AIP proceedings for ICPS 2012 - 31st International Conference on the Physics of Semiconductors, July 29-August 3, 2012 Zuric

    Interaction and coherence of a plasmon-exciton polariton condensate

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    Polaritons are quasiparticles arising from the strong coupling of electromagnetic waves in cavities and dipolar oscillations in a material medium. In this framework, localized surface plasmon in metallic nanoparticles defining optical nanocavities have attracted increasing interests in the last decade. This interest results from their sub-diffraction mode volume, which offers access to extremely high photonic densities by exploiting strong scattering cross-sections. However, high absorption losses in metals have hindered the observation of collective coherent phenomena, such as condensation. In this work we demonstrate the formation of a non-equilibrium room temperature plasmon-exciton-polariton condensate with a long range spatial coherence, extending a hundred of microns, well over the excitation area, by coupling Frenkel excitons in organic molecules to a multipolar mode in a lattice of plasmonic nanoparticles. Time-resolved experiments evidence the picosecond dynamics of the condensate and a sizeable blueshift, thus measuring for the first time the effect of polariton interactions in plasmonic cavities. Our results pave the way to the observation of room temperature superfluidity and novel nonlinear phenomena in plasmonic systems, challenging the common belief that absorption losses in metals prevent the realization of macroscopic quantum states.Comment: 23 pages, 5 figures, SI 7 pages, 5 figure

    Nanopatterning of colloidal nanocrystals emitters dispersed in a PMMA matrix by e-beam lithography

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    We report on the fabrication of periodic nanostructures embedding semiconductor colloidal nanocrystals (NCs) by directly exposing a polymer/NCs blend to electron beam lithography (EBL). Our technological approach for the fabrication of NCs-based photonic devices relies on the dispersion of CdSe/ZnS core/shell NCs into a layer of polymethilmethacrylate (PMMA) positive electron resist, which is patterned by means of an EBL process. The presence of NCs in the resist did not modify the peculiar behaviour of PMMA, which was selectively removed from the regions exposed to the electron beam. The morphology of the sample was assessed by scanning electron microscopy and atomic force microscopy measurements. The optical analysis of the samples after the dispersion of the NCs into the PMMA matrix and the exposure to the e-beam showed the successful localization of the colloidal NCs, whose emission properties were preserved

    Room temperature Bloch surface wave polaritons

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    Polaritons are hybrid light-matter quasi-particles that have gathered a significant attention for their capability to show room temperature and out-of-equilibrium Bose-Einstein condensation. More recently, a novel class of ultrafast optical devices have been realized by using flows of polariton fluids, such as switches, interferometers and logical gates. However, polariton lifetimes and propagation distance are strongly limited by photon losses and accessible in-plane momenta in usual microcavity samples. In this work, we show experimental evidence of the formation of room temperature propagating polariton states arising from the strong coupling between organic excitons and a Bloch surface wave. This result, which was only recently predicted, paves the way for the realization of polariton devices that could allow lossless propagation up to macroscopic distances

    Determination of band-offset enhanced in InGaAsP -InGaAsP strained multiquantum wells by photocurrent measurements

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    We experimentally determine the band offset of strain-compensated InGaAsP-InGaAsP multiquantum-well (MQW) heterostructures, emitting at 1.55 mum, that were grown by metal-organic chemical vapor deposition. A band offset value of about 56% is found for the conduction band, which is higher than the value reported for the unstrained structure. The temperature dependence of the photoluminescence intensity shows that the unipolar detrapping of carriers in such MQWs is more efficient than the thermal activation of excitons. (C) 2005 American Institute of Physic

    Local degradation of selectively oxidized AlGaAs/AlAs distributed Bragg reflectors in lateral-injection vertical-cavity surface-emitting lasers

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    We show the local degradation of a selectively oxidized top distributed Bragg reflector (DBR) in a lateral-junction vertical-cavity surface-emitting laser (LJ-VCSEL) working at room temperature in continuous-wave operation. The measurements were carried out by a scanning microluminescence system used in reflection mode. The injection of a few milliamps in continuous-wave operation at room temperature in the LJ-VCSEL induces damage both in the DBRs and in the active area. The submicron resolution maps of the reflected laser intensity, recorded from the top surface of the LJ-VCSEL, show a strong local change in the top DBR reflectivity before and after current injection. The ╬╝-photoluminescence map, recorded after the device failure, shows that the radiative recombination is strongly decreased in the damaged area of the device

    Ultrafast flow of interacting organic polaritons

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    The strong-coupling of an excitonic transition with an electromagnetic mode results in composite quasi-particles called exciton-polaritons, which have been shown to combine the best properties of their bare components in semiconductor microcavities. However, the physics and applications of polariton flows in organic materials and at room temperature are still unexplored because of the poor photon confinement in such structures. Here we demonstrate that polaritons formed by the hybridization of organic excitons with a Bloch Surface Wave are able to propagate for hundreds of microns showing remarkable third-order nonlinear interactions upon high injection density. These findings pave the way for the studies of organic nonlinear light-matter fluxes and for a technological promising route of dissipation-less on-chip polariton devices working at room temperature.Comment: Improved version with polariton-polariton interactions. 13 pages, 4 figures, supporting 6 pages, 6 figure
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