Dielectric GaAs Antenna Ensuring an Efficient Broadband Coupling between an InAs Quantum Dot and a Gaussian Optical Beam

We introduce the photonic trumpet, a dielectric structure which ensures a nearly perfect coupling between an embedded quantum light source and a Gaussian free-space beam. A photonic trumpet exploits both the broadband spontaneous emission control provided by a single-mode photonic wire and the adiabatic expansion of this mode within a conical taper. Numerical simulations highlight the outstanding performance and robustness of this concept. As a first application in the field of quantum optics, we report the realisation of an ultra-bright single-photon source. The device, a GaAs photonic trumpet containing few InAs quantum dots, demonstrates a first-lens external efficiency of $0.75 \pm 0.1$

Impact of surfaces on the optical properties of GaAs nanowires

The effect of surfaces on the optical properties of GaAs nanowires is evidenced by comparing nanowires with or without an AlGaAs capping shell as a function of the diameter. We find that the optical properties of unpassivated nanowires are governed by Fermi-level pinning, whereas, the optical properties of passivated nanowires are mainly governed by surface recombinations. Finally, we measure a surface recombination velocity of 3 x 10(3) cm s(-1) one order of magnitude lower than values previously reported for (110) GaAs surfaces. These results will serve as guidance for the application of nanowires in solar cell and light emitting devices

Genetic parameters for milk, fat and protein yields in Murrah buffaloes (Bubalus bubalis Artiodactyla, Bovidae)

The objective of the present study was to estimate genetic parameters for test-day milk, fat and protein yields and 305-day-yields in Murrah buffaloes. 4,757 complete lactations of Murrah buffaloes were analyzed. Co-variance components were estimated by the restricted maximum likelihood method. The models included additive direct genetic and permanent environmental effects as random effects, and the fixed effects of contemporary group, milking number and age of the cow at calving as linear and quadratic covariables. Contemporary groups were defined by herd-year-month of test for test-day yields and by herd-year-season of calving for 305-day yields. The heritability estimates obtained by two-trait analysis ranged from 0.15 to 0.24 for milk, 0.16 to 0.23 for protein and 0.13 to 0.22 for fat, yields. Genetic and phenotypic correlations were all positive. The observed population additive genetic variation indicated that selection might be an effective tool in changing population means in milk, fat and protein yields

Very Efficient Single-Photon Sources Based on Quantum Dots in Photonic Wires

International audienceWe review the recent development of high efficiency single photon sources based on a single quantum dot in a photonic wire. Unlike cavity-based devices, very pure single photon emission and efficiencies exceeding 0.7 photon per pulse are jointly demonstrated under non-resonant pumping conditions. By placing a tip-shaped or trumpet-like tapering at the output end of the wire, a highly directional Gaussian far-field emission pattern is obtained. More generally, a photonic wire containing a quantum dot appears as an attractive template to explore and exploit in a solid-state system the unique optical properties of "one-dimensional atoms"

ZnO/ZnSe type II core–shell nanowire array solar cell

International audienc

Determination of the Optimal Shell Thickness for Self-Catalyzed GaAs/AlGaAs Core-Shell Nanowires on Silicon

International audienceWe present a set of experimental results showing a combination of various effects, that is, surface recombination velocity, surface charge traps, strain, and structural defects, that govern the carrier dynamics of self-catalyzed GaAs/AlGaAs core-shell nano wires (NWs) grown on a Si(111) substrate by molecular beam epitaxy. Time-resolved photoluminescence of NW ensemble and spatially resolved cathodoluminescence of single NWs reveal that emission intensity, decay time, and carrier diffusion length of the GaAs NW core strongly depend on the AlGaAs shell thickness but in a nonmonotonic fashion. Although 7 nm AlGaAs shell can efficiently suppress the surface recombination velocity of the GaAs NW core, the influence of the surface charge traps and the strain between the core and the shell that redshift the luminescence of the GaAs NW core remain observable in the whole range of the shell thickness. In addition, the band bending effect induced by the surface charge traps can alter the scattering of the excess carriers inside the GaAs NW core at the core/shell interface. If the AlGaAs shell thickness is larger than SO nm, the luminescence efficiency of the GaAs NW cores deteriorates, ascribed to defect formation inside the AIGaAs shell evidenced by transmission electron microscopy

Development of NbN-based superconducting single photon detectors on silicon platform

International audienc

Effect of the barrier thickness on the performance of multiple-quantum-well InGaN photovoltaic cells

International audienceThe impact of the barrier thickness on the performance of In0.17Ga0.83N multiple-quantum-well (MQW) solar cells is studied. When the barrier thickness is reduced from 9.0 to 3.7 nm, the effect of the internal polarization fields on the MQW band structure results in a blueshift of the cell photoresponse. At the same time, the overlap of the fundamental electron and hole wave-functions in the quantum wells increases and the carrier extraction by field-assisted tunneling is enhanced, impacting the external quantum efficiency and fill-factor of the cells. The experimental results show that the performance of the thinner-barrier cells studied in this work is superior, or at least comparable to the performance of their thicker-barrier counterparts, in spite of the smaller total thickness of their absorbing region. This is due to their higher external quantum efficiency (37% at 370 nm) and improved fill-factor (62%), which result in a conversion efficiency of eta = 0.82%. (C) 2015 The Japan Society of Applied Physic

ZnO/ZnSe type II core-shell nanowire array solar cell

We report the realization of a prototype solar cell based on a ZnO/ZnSe core/shell nanowire array. The ZnO/ZnSe core/shell nanowire forms a type II heterojunci ion that can have an effective bandgap much below that of either component. The nanowire array architecture offers strong enhancement in light absorption through increasing the junction area and light trapping. The device shows a photo-response threshold of similar to 1.6 eV and a large open circuit voltage of 0.7 V. Type II optical transition at the ZnO/ZnSe interface is further confirmed by transmission, photoluminescence and time-resolved photoluminescence. This result opens up new options in selecting the absorber material for a solar cell. (C) 2011 Elsevier B.V. All rights reserved.Charlotte Research Institute; National Natural Science Foundations of China [60827004, 61106008]; Natural Science Foundations of Fujian Province [2010J01343]; fundamental research funds for the central universities [2011121042]; "Fondation Nanosciences" (France