la recherche des propriétés optiques et électriques sur les nanofils LEDs et photodétecteur

In this manuscript, I present my work dedicated to the realization and characterization of nitride nanowire light emitters and detectors. I detail the device fabrication using state-of-the-art nanofabrication tools as well as the investigation of their electrical and optical properties.First chapter briefly summarizes the nitride semiconductor basic properties and discusses the present status of nanowire elaboration. In the second chapter, I present my work on the fabrication and in-depth characterization of single nanowire InGaN/GaN LEDs with a transparent graphene contact for hole injection. Reference single wire LEDs with metal contacts are also investigated for comparison. The electroluminescence of single nanowire LEDs evidences the impact of the contact layout on the emission properties. In particular, the position of the contact determines the spectral evolution with injection current. Namely, for an extended contact and a contact localized on the m-plane, a transition from the green to blue emission is observed whereas for a localized contact on the m-plane/semipolar plane junction the emission remains green.In the third chapter, I describe the fabrication and characterize single wire LEDs made out of a vertical NW array with the contacting scheme identical to array LEDs. The emission shows a similar evolution as the lateral-contacted single nanowire LEDs. The dependence of the electroluminescence on the contact morphology opens the way to control the LED emission color at the device processing stage. I used fluorine plasma treatment to reduce the conductivity of the p-doped GaN shell for inhibiting the electrical injection in the In-rich region of the quantum well. Furthermore, I analyze the injection inhomogeneity effect. In order to avoid this effect, I developed a top down contacting scheme with electrons injected directly into n-GaN underlayer, which is called “front contacting” process. The “front contacting” LEDs show an enhanced yield of active nanowires from 19% to 65%.The last chapter is dedicated to the study of nitride nanowire photodetectors. I first describe the fabrication and characterization of a GaN ultraviolet (UV) photodetector based on a NW array with a transparent graphene contact. Moreover, single NW InGaN/GaN detectors were fabricated operating in the visible to ultraviolet spectral range. The influence of the contact morphology is also investigated by comparing two types of contacts, namely a partial metal contact and an indium tin oxide (ITO) conformal contact, respectively. In the last part, I present an up-to-date technique for fabricating flexible photodetectors based on vertical NW arrays and I discuss their performances.Dans ce manuscrit, je présente mon travail dédié à la réalisation et à la caractérisation des émetteurs et détecteurs de lumière à base de nanofils de nitrures. Je détaille la fabrication des dispositifs utilisant des outils de nanofabrication à l’état de l’art, ainsi que l'étude de leurs propriétés électriques et optiques.Le premier chapitre résume brièvement les propriétés de base des semi-conducteurs nitrures et décrit les méthodes d’élaboration des nanofils. Dans le deuxième chapitre, je présente mon travail sur la fabrication et la caractérisation de LED à nanofil unique InGaN/GaN ayant un contact transparent en graphène pour l’injection des trous. L'électroluminescence des LEDs à nanofils uniques montre l'impact de la forme du contact sur les propriétés d'émission. En particulier, la position du contact détermine l'évolution spectrale avec le courant d'injection. À savoir, pour un contact étendu et un contact localisé sur le plan m, l’émission passe du vert au bleu en fonction du courant d’injection alors que pour un contact localisé sur la jonction entre le plan m et le plan semipolaire l'émission reste verte.Dans le troisième chapitre, je décris la fabrication et la caractérisation des LEDs à nanofils uniques fabriqués à partir d'une matrice de nanofils verticaux avec une morphologie des contacts identique à celle mise en œuvre pour les LEDs à base d’ensemble de nanofils. L'émission montre une évolution similaire à celle observée pour les LEDs à nanofils uniques avec un contact latéral. L’influence de la morphologie des contacts sur l'électroluminescence ouvre la possibilité de contrôler la couleur d'émission de la LED à l'étape de la fabrication. J'ai utilisé un traitement par plasma de fluor afin de réduire la conductivité de la coquille GaN dopé p et d’inhiber l'injection électrique dans la région riche en In du puits quantique. En outre, j'ai analysé l'effet de l’inhomogénéité d'injection. Afin d'améliorer l’homogénéité, j'ai développé un système de contact par le haut permettant d’injecter les électrons directement dans la sous-couche n-GaN. Les LEDs fabriquées selon cette procédure montrent un rendement amélioré avec 65% de nanofils actifs contre 19% pour une procédure standard.Le dernier chapitre est consacré à l'étude des photodétecteurs à nanofils de nitrure. Je décris d'abord la fabrication et la caractérisation d'un photodétecteur de rayonnement ultraviolet basé sur un ensemble de nanofils de GaN avec un contact transparent en graphène. Ensuite, des détecteurs à nanofils uniques InGaN / GaN ont été fabriqués fonctionnant dans la gamme spectrale du visible à ultraviolet. L'influence de la morphologie de contact est également étudiée en comparant deux types de contacts, à savoir un contact métallique localisé et un contact étendu en oxyde d'indium-étain (ITO). Dans la dernière partie, je présente une technique pour la fabrication de photodétecteurs flexibles basée sur des ensembles de nanofils verticaux et je discute leurs performances

Adaptive Channel Encoding Transformer for Point Cloud Analysis

Transformer plays an increasingly important role in various computer vision areas and remarkable achievements have also been made in point cloud analysis. Since they mainly focus on point-wise transformer, an adaptive channel encoding transformer is proposed in this paper. Specifically, a channel convolution called Transformer-Conv is designed to encode the channel. It can encode feature channels by capturing the potential relationship between coordinates and features. Compared with simply assigning attention weight to each channel, our method aims to encode the channel adaptively. In addition, our network adopts the neighborhood search method of low-level and high-level dual semantic receptive fields to improve the performance. Extensive experiments show that our method is superior to state-of-the-art point cloud classification and segmentation methods on three benchmark datasets.Comment: ICANN202

Dual-Neighborhood Deep Fusion Network for Point Cloud Analysis

Recently, deep neural networks have made remarkable achievements in 3D point cloud classification. However, existing classification methods are mainly implemented on idealized point clouds and suffer heavy degradation of per-formance on non-idealized scenarios. To handle this prob-lem, a feature representation learning method, named Dual-Neighborhood Deep Fusion Network (DNDFN), is proposed to serve as an improved point cloud encoder for the task of non-idealized point cloud classification. DNDFN utilizes a trainable neighborhood learning method called TN-Learning to capture the global key neighborhood. Then, the global neighborhood is fused with the local neighbor-hood to help the network achieve more powerful reasoning ability. Besides, an Information Transfer Convolution (IT-Conv) is proposed for DNDFN to learn the edge infor-mation between point-pairs and benefits the feature transfer procedure. The transmission of information in IT-Conv is similar to the propagation of information in the graph which makes DNDFN closer to the human reasoning mode. Extensive experiments on existing benchmarks especially non-idealized datasets verify the effectiveness of DNDFN and DNDFN achieves the state of the arts.Comment: ICMEW202

Flexible Light-Emitting Diodes Based on Vertical Nitride Nanowires

International audienceWe demonstrate large area fully flexible blue LEDs based on core/shell InGaN/GaN nanowires grown by MOCVD. The fabrication relies on polymer encapsulation, nanowire lift-off and contacting using silver nanowire transparent electrodes. The LEDs exhibit rectifying behavior with a light-up voltage around 3 V. The devices show no electro-luminescence degradation neither under multiple bending down to 3 mm curvature radius nor in time for more than one month storage in ambient conditions without any protecting encapsulation. Fully transparent flexible LEDs with high optical transmittance are also fabricated. Finally, a two-color flexible LED emitting in the green and blue spectral ranges is demonstrated combining two layers of InGaN/GaN nanowires with different In contents. F lexible light-emitting diodes (LEDs) are today a topic of intense research, motivated by their numerous economically relevant applications (e.g., rollable displays, wearable intelligent electronics, lightning, and so forth). Presently, flexible devices mainly use organic materials integrated on lightweight and flexible plastic substrates. Thanks to the flexibility, relative ease of processing, compatibility with various flexible substrates, and their low cost, organic LEDs (OLEDs) are today the key technology for flexible displays. In the past decades, the OLED performance has been tremendously improved. 1−4 However, they still face the issue of a poor time stability caused by the degradation of the electrical conductivity of the organic layers and of the interface degradation in the active region. 5−7 Especially, OLEDs present limitations in the short wavelength range, which has a detrimental influence on the color balance of the displays. Indeed, blue OLEDs suffer from a rather low luminance (around 10

InGaN/GaN core/shell nanowires for visible to ultraviolet range photodetection

International audienceWe report on the fabrication and characterization of single nitride nanowire visible-to-ultraviolet p-n photodetec-tors. Nitride nanowires containing 30 InGaN/GaN radial quantum wells with 18% indium fraction were grown by catalyst-free metal-organic vapour phase epitaxy. Single nanowires were contacted using optical lithography. As expected for a radial p-n junction, the current-voltage (I-V) curves of single wire detectors show a rectifying behavior in the dark and a photocurrent under illumination. The detectors present a response in the visible to UV spectral range starting from 2.8 eV. The peak responsivity is 0.17 A/W at 3.36 eV. The on-off switching time under square light pulses is found to be below 0.1 sec

Substrate-Free InGaN/GaN Nanowire Light-Emitting Diodes

International audienceWe report on the demonstration of substrate-freenanowire /polydimethylsiloxane (PDMS) membrane light emitting diodes (LEDs). Metal-organic vapor phase epitaxy (MOVPE)-grown InGaN/GaN core−shell nanowires were encapsulated into PDMS layer. After metal deposition to p-GaN, a thick PDMS cap layer was spin-coated and the membrane was manually peeled from the sapphire substrate, flipped upside down onto a steel holder, and transparent ITO contact to n-GaN was deposited. The fabricated LEDs demonstrate rectifying diode characteristics. For the electroluminescence (EL) measurements the samples were manually bonded using silver paint.The EL spectra measured at different applied voltages demonstrate a blue-shift with the current increase. This shift is explained by the current injection into the InGaN areas of the active region with different average Indium content

Bilateral striatal necrosis due to homoplasmic mitochondrial 3697G\u3eA mutation presents with incomplete penetrance and sex bias

© 2019 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals, Inc. Background: Heteroplasmic mitochondrial 3697G\u3eA mutation has been associated with leber hereditary optic neuropathy (LHON), mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS), and LHON/MELAS overlap syndrome. However, homoplasmic m.3697G\u3eA mutation was only found in a family with Leigh syndrome, and the phenotype and pathogenicity of this homoplasmic mutation still need to be investigated in new patients. Methods: The clinical interviews were conducted in 12 individuals from a multiple-generation inherited family. Mutations were screened through exome next-generation sequencing and subsequently confirmed by PCR-restriction fragment length polymorphism. Mitochondrial complex activities and ATP production rate were measured by biochemical analysis. Results: The male offspring with bilateral striatal necrosis (BSN) were characterized by severe spastic dystonia and complete penetrance, while the female offspring presented with mild symptom and low penetrance. All offspring carried homoplasmic mutation of NC_012920.1: m.3697G\u3eA, p.(Gly131Ser). Biochemical analysis revealed an isolated defect of complex I, but the magnitude of the defect was higher in the male patients than that in the female ones. The ATP production rate also exhibited a similar pattern. However, no possible modifier genes on the X chromosome were identified. Conclusion: Homoplasmic m.3697G\u3eA mutation could be associated with BSN, which expanded the clinical spectrum of m.3697G\u3eA. Our preliminary investigations had not found the underlying modifiers to support the double hit hypothesis, while the high level of estrogens in the female patients might exert a potential compensatory effect on mutant cell metabolism

Flexible White Light Emitting Diodes Based on Nitride Nanowires and Nanophosphors

International audienceWe report the first demonstration of a flexible white phosphor-converted light emitting diodes (LEDs) based on p-n junction core/shell nitride nanowires. GaN nanowires containing 7 radial In 0.2 Ga 0.8 N/GaN quantum wells were grown by metal-organic chemical vapor deposition on a sapphire substrate by a catalyst-free approach. To fabricate the flexible LED, the nanowires are embedded into a phosphor-doped polymer matrix, peeled off from the growth substrate and contacted using flexible and transparent silver nanowire mesh. The electroluminescence of a flexible device presents a cool-white color with a spectral distribution covering a broad spectral range from 400 to 700 nm. Mechanical bending stress down to a curvature radius of 5 mm doesnot yieldany degradation of the LED performance. The maximal measured external quantum efficiency (EQE) of the white LED is 9.3% and the wall plug efficiency is 2.4%

Effect of unilateral training and bilateral training on physical performance: A meta-analysis

Background: In Unilateral (UNI) exercises are more effective than bilateral (BI) exercises in improving athletic performance is debatable.Objectives: this meta-analysis investigated the effects of UNI and BI exercises on different effect indicators of jump ability, sprint ability, maximal force, change of direction ability, and balance ability.Data Sources: PubMed, Google Scholar, Web of science, CNKI, Proquest, Wan Fang Data.Study Eligibility Criteria: To be eligible for inclusion in the meta-analysis, the study had to be: 1) athletes; 2) UNI training and BI training; 3) the intervention period had to be more than 6 weeks and the intervention frequency had to be more than 2 times/week; 4) the outcome indicators were jumping ability, sprinting ability, maximum strength, and change of direction and balance.Study Appraisal and Synthesis Method: We used the random-effects model for meta-analyses. Effect sizes (standardized mean difference), calculated from measures of horizontally oriented performance, were represented by the standardized mean difference and presented alongside 95% confidence intervals (CI).Results: A total of 28 papers met the inclusion criteria, and Meta-analysis showed that UNI training was more effective than BI training in improving jumping ability (ES = 0.61.0.23 to 0.09; Z = 3.12, p = 0.002 < 0.01), sprinting ability (ES = −0.02, −0.03 to −0.01; Z = 2.73, p = 0.006 < 0.01), maximum strength (ES = 8.95,2.30 to 15.61; Z = 2.64, p = 0.008 > 0.05), change of direction ability (ES = −0.03, −0.06 to 0.00; Z = 1.90, p = 0.06 > 0.01) and balance ability (ES = 1.41,-0.62 to 3.44; Z = 1.36, p = 0.17 > 0.01). The results of the analysis of moderating variables showed that intervention period, intervention frequency and intervention types all had different indicators of effect on exercise performance.Conclusion: UNI training has a more significant effect on jumping and strength quality for unilateral power patterns, and BI training has a more significant effect on jumping and strength quality for bilateral power patterns

Flexible Photodiodes Based on Nitride Core/Shell p-n Junction Nanowires

International audienceA flexible nitride p-n photodiode is demonstrated. The device consists of a composite nanowire/polymer membrane trans- ferred onto a flexible substrate. The active element for light sensing is a vertical array of core/shell p−n junction nanowires containing InGaN/ GaN quantum wells grown by MOVPE. Electron/hole generation and transport in core/shell nanowires are modeled within nonequilibrium Green function formalism showing a good agreement with experimental results. Fully flexible transparent contacts based on a silver nanowire network are used for device fabrication, which allows bending the detector to a few millimeter curvature radius without damage. The detector shows a photoresponse at wavelengths shorter than 430 nm with a peak responsivity of 0.096 A/W at 370 nm under zero bias. The operation speed for a 0.3 × 0.3 cm2 detector patch was tested between 4 Hz and 2 kHz. The −3 dB cutoff was found to be ∼35 Hz, which is faster than the operation speed for typical photoconductive detectors and which is compatible with UV monitoring applications