233 research outputs found
Electrically injected cavity polaritons
We have realised a semiconductor quantum structure that produces
electroluminescence while operating in the light-matter strong coupling regime.
The mid-infrared light emitting device is composed of a quantum cascade
structure embedded in a planar microcavity, based on the GaAs/AlGaAs material
system. At zero bias, the structure is characterised using reflectivity
measurements which show, up to room temperature, a wide polariton anticrossing
between an intersubband transition and the resonant cavity photon mode. Under
electrical injection the spectral features of the emitted light change
drastically, as electrons are resonantly injected in a reduced part of the
polariton branches. Our experiment demonstrates that electrons can be
selectively injected into polariton states up to room temperature.Comment: 10 pages, 4 figure
II WORKSHOP ON CHEMICAL SENSORS AND BIOSENSORS ELLIPSOMETRIC AND SURFACE PLASMON RESONANCE EFFECTS ON LB FILMS OF ORGANIC MATERIALS IN CONTROLLED ATMOSPHERE
ABSTRACT: Langmuir-Blodgett (LB) films of Cu(II) tetrakis-(3,3-dimethyl-1-butoxicarbonyl)phthalocyanine have been studied as regard their optical property. In particular electronic spectra in the UV-VIS spectral range and the optical constant of the LB multilayers have been carried out. In order to use these LB films as optical gas sensors, ellipsometric and surface plasmon resonance (SPR) measurements were carried out in controlled atmosphere. SPR measurements were conducted by using a system based on the Kretschmann configuration. LB monolayers of Cu(dmbc)Pc deposited as selective layer on a metal surface show changes of the reflectance on exposure to nitrogen dioxide mixed with dry air in low concentration. Moreover, ellipsometric measurements carried out on LB multilayers of Cu(dmbc)Pc deposited onto silicon substrates, have shown variation at a fixed wavelength in the thickness and complex refractive index when are exposed to different concentrations of toluene and tetrachloroethene
Direct surface cyclotron resonance terahertz emission from a quantum cascade structure
A strong magnetic field applied along the growth direction of a semiconductor
quantum well gives rise to a spectrum of discrete energy states, the Landau
levels. By combining quantum engineering of a quantum cascade structure with a
static magnetic field, we can selectively inject electrons into the excited
Landau level of a quantum well and realize a tunable surface emitting device
based on cyclotron emission. By applying the appropriate magnetic field between
0 and 12 T, we demonstrate emission from a single device over a wide range of
frequencies (1-2 THz and 3-5 THz)
Bound-to-bound and bound-to-continuum optical transitions in combined quantum dot - superlattice systems
By combining band gap engineering with the self-organized growth of quantum
dots, we present a scheme of adjusting the mid-infrared absorption properties
to desired energy transitions in quantum dot based photodetectors. Embedding
the self organized InAs quantum dots into an AlAs/GaAs superlattice enables us
to tune the optical transition energy by changing the superlattice period as
well as by changing the growth conditions of the dots. Using a one band
envelope function framework we are able, in a fully three dimensional
calculation, to predict the photocurrent spectra of these devices as well as
their polarization properties. The calculations further predict a strong impact
of the dots on the superlattices minibands. The impact of vertical dot
alignment or misalignment on the absorption properties of this dot/superlattice
structure is investigated. The observed photocurrent spectra of vertically
coupled quantum dot stacks show very good agreement with the calculations.In
these experiments, vertically coupled quantum dot stacks show the best
performance in the desired photodetector application.Comment: 8 pages, 10 figures, submitted to PR
Quasi-static and propagating modes in three-dimensional THz circuits
We provide an analysis of the electromagnetic modes of three-dimensional metamaterial resonators in the THz frequency range. The fundamental resonance of the structures is fully described by an analytical circuit model, which not only reproduces the resonant frequencies but also the coupling of the metamaterial with an incident THz radiation. We also demonstrate the contribution of the propagation effects, and show how they can be reduced by design. In the optimized design, the electric field energy is lumped into ultra-subwavelength (λ/100) capacitors, where we insert a semiconductor absorber based on the collective electronic excitation in a two dimensional electron gas. The optimized electric field confinement is exhibited by the observation of the ultra-strong light-matter coupling regime, and opens many possible applications for these structures in detectors, modulators and sources of THz radiation
Microphotoluminescence spectroscopy of vertically stacked In x Ga 1 â x A s / G a A s quantum wires
Disorder and spectral broadening of vertically stacked InGaAs/GaAs V-grooved quantum wires have been investigated by means of microprobe luminescence. We show that the main spectral broadening mechanism originates from monolayer fluctuations at the bottom of the wire. A direct evidence of monolayer height islands of area 40\ifmmode\times\else\texttimes\fi{}40\mathrm{nm} formed at the bottom of the grooves is provided by atomic force microscopy. Lateral and vertical wire-to-wire fluctuations are found to be negligible on the micron scale
Determination of surface lattice strain in ZnTe epilayers on {100}GaAs by ion channeling and reflectance spectroscopy
We report on the direct measurements of surface lattice strain in ZnTe epitaxial layers on {100}GaAs substrates by ion channeling Rutherford backscattering spectrometry and lowâtemperature (10 K) reflectance spectroscopy measurements. The measured ZnTe strain is the superposition of the expected thermal (tensile) strain and a thicknessâdependent residual compressive strain. Our data indicate that the removal of this residual strain is slower than the rate predicted by the equilibrium theory, following an apparent hâ1/2 powerâlaw dependence on the epilayer thickness h, above âŒ100 nm
Ultra-strong lightâmatter coupling for designer Reststrahlen band
The strength of the lightâmatter interaction depends on the number of dipoles that can couple with the photon trapped in an optical cavity. The coupling strength can thus be maximized by filling the entire cavity volume with an ensemble of interacting dipoles. In this work this is achieved by inserting a highly doped semiconductor layer in a subwavelength plasmonic resonator. In our system the ultra-strong lightâmatter coupling occurs between a collective electronic excitation and the cavity photon. The measured coupling strength is 73% of the matter excitation energy, the highest ever reported for a lightâmatter coupled system at room temperature. We experimentally and theoretically demonstrate that such an ultra-strong interaction modifies the optical properties on a very wide spectral range (20â250 meV), and results in the appearance of a photonic gap of 38 meV, independently of the light polarization and angle of incidence. Lightâmatter ultra-strong coupling can thus be exploited to conceive metasurfaces with an engineered reflectivity band
Antenna-Coupled Microcavity Enhanced THz Photodetectors
Plasmonic THz photodetectors have been realized in this work, by implementing the active region of a 5 THz quantum well detector with an antenna-coupled microcavity array. Our results demonstrate a clear improvement in responsivity, polarization insensitivity and background limited performance
Ultra-Strong Light-Matter Coupling in Deeply Subwavelength THz LC Resonators
International audienceThe ultra-strong light-matter coupling regime has been demonstrated in a novel three-dimensional inductor-capacitor (LC) circuit resonator, embedding a semiconductor two-dimensional electron gas in the capacitive part. The fundamental resonance of the LC circuit interacts with the intersubband plasmon excitation of the electron gas at Ï c = 3.3 THz with a normalized coupling strength 2⊠R /Ï c = 0.27. Light matter interaction is driven by the quasi-static electric field in the capacitors, and takes place in a highly subwavelength effective volume V eff = 10 â6 λ 3 0. This enables the observation of the ultra-strong light-matter coupling with 2.4 Ă 10 3 electrons only. Notably, our fabrication protocol can be applied to the integration of a semiconductor region into arbitrary nano-engineered three dimensional meta-atoms. This circuit architecture can be considered the building block of metamaterials for ultra-low dark current detectors
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