Optical extinction in a single layer of nanorods

We demonstrate that almost 100 % of incident photons can interact with a monolayer of scatterers in a symmetrical environment. Nearly-perfect optical extinction through free-standing transparent nanorod arrays has been measured. The sharp spectral opacity window, in the form of a characteristic Fano resonance, arises from the coherent multiple scattering in the array. In addition, we show that nanorods made of absorbing material exhibit a 25-fold absorption enhancement per unit volume compared to unstructured thin film. These results open new perspectives for light management in high-Q, low volume dielectric nanostructures, with potential applications in optical systems, spectroscopy, and optomechanics

Cu(In,Ga)Se 2 mesa microdiodes: study of edge recombination and behaviour under concentrated sunlight

ABSTRACT In order to develop photovoltaic devices with increased efficiency using less rare semiconductor materials, the concentrating approach is applied on Cu(In,Ga)Se2 thin film devices. For this purpose, Cu(In,Ga)Se2 microcells with a mesa design are fabricated. The influence of the edge recombination signal is analyzed. It is found that with an appropriate etching procedure, devices as small as 50x50 µm do not experience edge recombination efficiency limitations. Under concentration, significant Voc gains are seen, leading to an absolute efficiency increase of two points per decade

Compact planar lenses based on a pinhole and an array of single mode metallic slits

Plasmonic lenses are based on complex combinations of nanoscale high aspect ratio slits. We show that their design can be greatly simplified, keeping similar performance while releasing technological constraints. The simplified system, called Huygens lens, consists in a central aperture surrounded by several identical single mode slits in a thin gold layer that does not rely anymore on surface plasmons. The focusing behaviour with respect to the position and number of slits is investigated, and we demonstrate the interest of this design to get compact array of lenses

Strong Discontinuities in the Complex Photonic Band Structure of Transmission Metallic Gratings

Complex photonic band structures (CPBS) of transmission metallic gratings with rectangular slits are shown to exhibit strong discontinuities that are not evidenced in the usual energetic band structures. These discontinuities are located on Wood's anomalies and reveal unambiguously two different types of resonances, which are identified as horizontal and vertical surface-plasmon resonances. Spectral position and width of peaks in the transmission spectrum can be directly extracted from CPBS for both kinds of resonances.Comment: 4 pages, 4 figures, REVTeX version

Efficient light absorption in metal-semiconductor-metal nanostructures

International audienceA nanoscale metal-semiconductor grating is proposed for efficient and ultrafast photodetection. Theoretical and experimental results of efficient absorption in nanoscopic semiconductor wires are presented. The strong confinement of light in subwavelength metal-semiconductor gratings is achieved by Fabry-Pérot resonances involving vertical transverse magnetic surface-plasmon waves and transverse electric guided waves. Photodetectors have been fabricated with 40×100 nm cross sections of Ag and GaAs wires. The reflectivity and photocurrent mesurements are in good agreement with theoretical estimates

Horizontal and vertical surface resonances in transmission metallic gratings

International audienceIn transmission metallic gratings, quasi-total transmission of light is achieved by two different mechanisms, which are the excitation of horizontal and vertical surface-plasmon resonances. Both resonances are represented on complex photonic band structures for a wide range of grating thicknesses. The evolution of the electromagnetic field intensity provides a physical understanding of the behaviour of dispersion curves and of lifetime discontinuities in Wood-Rayleigh anomalies in particular. Both radiative and non-radiative processes are distinguished in the resonances' width, giving limits for the use of metallic gratings in photonic devices

Experimental study of hot electron inelastic scattering rate in p-type InGaAs

International audienceThe inelastic scattering rates of electrically injected minority hot electrons measured using a continuous-wave spatially resolved electroluminescence spectroscopy are reported. To our knowledge, this constitutes direct experimental determination of this parameter related to the individual inelastic interactions. The evolution of the electron relaxation rate with increasing majority hole density is explored. Remarkably, an attenuation of the scattering rate is measured for p-doping levels higher than 2×1019 cm-3. Additionally, the measured hot-electron energy distributions further indicate that the relaxation mechanisms are dominated by LO phonon-plasmons coupled modes in the range 1018 to 1019 cm-3 hole density. Finally, the temperature dependence of inelastic scattering rate is also measured to learn on the potential implication of ballistic transport in RT operating hot-electron devices

XPS chemical state mapping in opto- and microelectronics

International audienceDans le but d’approcher des compositions chimiques de surface de quelques millimètres carrés, l’imagerie XPS est un atout indéniable. Ces mesures de photoémission peuvent s’avérer utiles pour i) localiser avec confiance des objets micrométriques, ii) connaître la distribution spatiale des éléments constitutifs de la surface (cartographie élémentaire) et iii) différencier localement des environnements chimiques.Les différents modes d’acquisition d’images (snap map vs parallel imaging), développés grâce à la diminution des tailles de spot de rayons X (jusqu’à la dizaine de microns) ou l’utilisation conjointe d’une lentille et d’un détecteur 2D, ouvrent la porte à la caractérisation de motifs dans une large gamme d'applications industrielles et en particulier dans le domaine de la micro- optoélectronique. Les dimensions caractéristiques mises en jeu dans ce type de dispositifs nécessitent généralement une analyse sur des zones trop fines pour être caractérisées avec des outils traditionnels tels que la microscopie électronique à balayage couplée à de la spectroscopie de rayons X à dispersion d'énergie (MEB-EDS). Par ailleurs, le recours souvent nécessaire à des couches de passivation isolantes (oxydes, nitrures…) rend l’utilisation de la spectroscopie d’électrons Auger (AES) assez délicate à mettre en œuvre. Dans ces conditions, malgré une résolution latérale nettement plus faible, l’imagerie XPS avec un canon à neutralisation de charges s’avère être une technique de choix.Dans cette présentation, nous montrerons l’intérêt de la cartographie XPS dans le cadre de la structuration de matériaux III-V. En effet, il est rapporté que le traitement électrochimique anodique du phosphure d’indium (InP) dans NH3 liquide permet la croissance d’une couche ultramince de type polyphosphazène (PPP) en surface du semiconducteur1. L'extrême stabilité chimique de ce film d’épaisseur nanométrique en fait un matériau propice pour réaliser des masques pour la gravure humide d’InP2. La structuration du PPP grâce à des techniques de dépôt sélectif, étape clé dans le procédé technologique, sera démontrée par imagerie XPS des niveaux de cœur N1s et P2p (Figure 1).Par ailleurs, nous détaillerons l’apport de la cartographie XPS pour la caractérisation d’hétérostructures d’oxydes pérovskites, classe de matériaux prometteurs pour l’électronique du futur. L’imagerie XPS des niveaux de cœur Ti2p et V2p sur l’empilement (SrTiO3/SrVO3) met clairement en évidence les deux domaines (Figure 2). La cartographie XPS du niveau de cœur Sr3d sera discutée : le strontium étant commun aux deux oxydes et dans des environnements chimiques3,4 très proches

High electron mobility in pseudomorphic modulation‐doped In 0.75 Ga 0.25 As/InAlAs heterostructures achieved with growth interruptions

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