177 research outputs found
Understanding Polarization Properties of InAs Quantum Dots by Atomistic Modeling of Growth Dynamics
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
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
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
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
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
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 μ-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
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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