Road Map for Nanocrystal Based Infrared Photodetectors

Infrared (IR) sensors based on epitaxially grown semiconductors face two main challenges which are their prohibitive cost and the difficulty to rise the operating temperature. The quest for alternative technologies which will tackle these two difficulties requires the development of new IR active materials. Over the past decade, significant progresses have been achieved. In this perspective, we summarize the current state of the art relative to nanocrystal based IR sensing and stress the main materials, devices and industrial challenges which will have to be addressed over the 5 next years

Field effect transistor and photo transistor of narrow band gap nanocrystal arrays using ionic glasses

International audienceGating of nanocrystal films is currently driven by two approaches: either the use of a dielectric such as SiO2 or the use of electrolyte. SiO2 allows fast bias sweeping over a broad range of temperatures but requires a large operating bias. Electrolyte, thanks to a large capacitance, leads to significantly reduce operating bias but is limited to slow speed and quasi room temperature operation. None of these operating conditions are optimal for narrow band gap nanocrystal-based phototransistors for which the need of a large capacitance gate has to be combined with low temperature operation. Here we explore the use of a LaF3 ionic glass as a high capacitance gating alternative. We demonstrate for the first time the use of such ionic glasses to gate thin films made of HgTe and PbS nanocrystals. This gating strategy allows operation in the 180 to 300 K range of temperatures with capacitance as high as 1 µF·cm-2. We unveil the unique property of ionic glass gate to enable unprecedented tunability of both magnitude and dynamics of the photocurrent, thanks to high charge doping capability within an operating temperature window relevant for infrared photodetection. We demonstrate that by carefully choosing the operating gate bias, the signal to noise ratio can be improved by a factor 100 and the time response accelerated by a factor 6. Moreover, the good transparency of LaF3 substrate allows back side illumination in the infrared which is highly valuable for the design of phototransistor

Transport and Phototransport in ITO Nanocrystals with Short to Long-Wave Infrared Absorption

Nanocrystals are often described as an interesting strategy for the design of low-cost optoelectronic devices especially in the infrared range. However the driving materials reaching infrared absorption are generally heavy metalcontaining (Pb and Hg) with a high toxicity. An alternative strategy to achieve infrared transition is the use of doped semiconductors presenting intraband or plasmonic transition in the short, mid and long-wave infrared. This strategy may offer more flexibility regarding the range of possible candidate materials. In particular, significant progresses have been achieved for the synthesis of doped oxides and for the control of their doping magnitude. Among them, tin doped indium oxide (ITO) is the one providing the broadest spectral tunability. Here we test the potential of such ITO nanoparticles for photoconduction in the infrared. We demonstrate that In2O3 nanoparticles presents an intraband absorption in the mid infrared range which is transformed into a plasmonic feature as doping is introduced. We have determined the cross section associated with the plasmonic transition to be in the 1-3x10-13 cm2 range. We have observed that the nanocrystals can be made conductive and photoconductive due to a ligand exchange using a short carboxylic acid, leading to a dark conduction with n-type character. We bring further evidence that the observed photoresponse in the infrared is the result of a bolometric effect

Impact Assessment of Disruptive Technologies on Electronic Identities (eID) for the Improvement of Digital Public Services for Citizens

Public services are increasingly being transformed into smart public services, also known as digital public services or eGovernment. In several cases, access to specific services is personal and non-transferable, thus requiring secure and trustful identification as well as management of the so called “digital identities”. In this context, it is obvious that citizens and public services in particular would benefit greatly from digital identity management technology, as new and emerging technologies have strong potential to empower existing eID systems. Yet, while opportunities enabled by these technologies are undeniable, challenges also exist, including technological and social implications, as well as barriers, risks and limitations. In addition, the establishment of standards for these ecosystems and compliance with framework conditions, including national and European regulations are essential points that must be considered. Based on these observations, the IMPULSE (Identity Management in PUblic SErvices) project, funded under the Horizon 2020 programme, was launched in early 2020. IMPULSE aims to perform a multidisciplinary evaluation of the disruptive transformation of electronic identity (eID) management in public services enabled by Distributed Ledger Technology (DLT) and Artificial Inteligence (AI). Overall, this paper will present the research pathway set up to answer the question of how a single adaptive eID solution can be useful to the whole city ecosystem, from the micro-citizen level to the macro-governmental perspective, by focusing on the main achievements of the IMPULSE project so far

Étude des propriétés optoélectroniques de nanocristaux colloïdaux à faible bande interdite : application à la détection infrarouge

Colloidal semiconductor nanocrystals are nanomaterials synthesized in solution. Below a certain size, these nanocrystals acquire quantum confinement properties: their optoelectronic properties depend on the nanoparticle size. In the visible range, colloidal nanocrystals are quite mature. The next objective in this field is to get infrared colloidal nanocrystals. Mercury selenide (HgSe) and mercury telluride (HgTe) are potential candidates. The goal of this PhD work is to strengthen our knowledge on optical, optoelectronic and transport properties of these nanocrystals, in order to design an infrared detector.To do so, we studied the electronic structure of HgSe and HgTe for different sizes and surface chemistries. We can then determine the energies of the electronic levels and the Fermi energy, quantify doping level … We show that the nanocrystal size has an influence on doping level, which gets more and more n-type as the nanocrystal size gets larger. We even observe a semiconductor-metal transition in HgSe nanocrystals as the size is increased. The doping control with surface chemistry is then investigated. By using dipolar effects or oxidizing ligands, we show a doping control over several orders of magnitude. Thanks to these studies, we are able to propose a HgTe based device for detection at 2.5 µm, which structure allows to convert effectively the absorbed photons into an electrical current and to get a high signal over noise ratio. We get a photoresponse of 20 mA/W and a detectivity of 3 × 10 9 Jones.Les nanocristaux colloïdaux de semiconducteurs sont des nanomatériaux synthétisés en solution. En deçà d’une certaine taille, ils deviennent confinés : leurs propriétés optiques et électroniques sont alors dépendantes de leur taille. Le développement de ces nanocristaux a atteint une grande maturité dans le visible. L’enjeu est maintenant d’étendre la gamme accessible et d’obtenir des nanocristaux ayant des propriétés dans l’infrarouge. Parmi les candidats, on trouve les nanocristaux de tellure de mercure, HgTe, et de séléniure de mercure, HgSe. L’objectif de ce doctorat est d’approfondir la connaissance des propriétés optoélectroniques et de transport de ces matériaux afin de concevoir un système de détection infrarouge. Pour y parvenir, la structure électronique de ces matériaux est mesurée pour différentes tailles et différents ligands. Nous pouvons alors déterminer les énergies des niveaux électroniques et quantifier le niveau de dopage. Nous montrons que ce dopage dépend de la taille des cristaux, qu’il devient de plus en plus n quand la taille du cristal augmente. Dans le cas de HgSe, cette évolution du dopage avec la taille se traduit par une transition semiconducteur-métal. Le contrôle du dopage est ensuite étudié en fonction de la chimie de surface. En utilisant des effets dipolaires ou des transferts d’électrons via des ligands oxydants, nous montrons une modulation du dopage sur plusieurs ordres de grandeur. Ces études nous permettent de proposer un détecteur infrarouge à base de HgTe, fonctionnant à 2.5 µm, dont la structure permet de convertir les photons absorbés en courant. Nous obtenons une réponse de 20 mA/W et une détectivité de 3 × 10 9 Jones

Optoelectronic properties of narrow band gap nanocrystals : application to infrared detection

Les nanocristaux colloïdaux de semiconducteurs sont des nanomatériaux synthétisés en solution. En deçà d’une certaine taille, ils deviennent confinés : leurs propriétés optiques et électroniques sont alors dépendantes de leur taille. Le développement de ces nanocristaux a atteint une grande maturité dans le visible. L’enjeu est maintenant d’étendre la gamme accessible et d’obtenir des nanocristaux ayant des propriétés dans l’infrarouge. Parmi les candidats, on trouve les nanocristaux de tellure de mercure, HgTe, et de séléniure de mercure, HgSe. L’objectif de ce doctorat est d’approfondir la connaissance des propriétés optoélectroniques et de transport de ces matériaux afin de concevoir un système de détection infrarouge. Pour y parvenir, la structure électronique de ces matériaux est mesurée pour différentes tailles et différents ligands. Nous pouvons alors déterminer les énergies des niveaux électroniques et quantifier le niveau de dopage. Nous montrons que ce dopage dépend de la taille des cristaux, qu’il devient de plus en plus n quand la taille du cristal augmente. Dans le cas de HgSe, cette évolution du dopage avec la taille se traduit par une transition semiconducteur-métal. Le contrôle du dopage est ensuite étudié en fonction de la chimie de surface. En utilisant des effets dipolaires ou des transferts d’électrons via des ligands oxydants, nous montrons une modulation du dopage sur plusieurs ordres de grandeur. Ces études nous permettent de proposer un détecteur infrarouge à base de HgTe, fonctionnant à 2.5 µm, dont la structure permet de convertir les photons absorbés en courant. Nous obtenons une réponse de 20 mA/W et une détectivité de 3 × 10 9 Jones.Colloidal semiconductor nanocrystals are nanomaterials synthesized in solution. Below a certain size, these nanocrystals acquire quantum confinement properties: their optoelectronic properties depend on the nanoparticle size. In the visible range, colloidal nanocrystals are quite mature. The next objective in this field is to get infrared colloidal nanocrystals. Mercury selenide (HgSe) and mercury telluride (HgTe) are potential candidates. The goal of this PhD work is to strengthen our knowledge on optical, optoelectronic and transport properties of these nanocrystals, in order to design an infrared detector.To do so, we studied the electronic structure of HgSe and HgTe for different sizes and surface chemistries. We can then determine the energies of the electronic levels and the Fermi energy, quantify doping level … We show that the nanocrystal size has an influence on doping level, which gets more and more n-type as the nanocrystal size gets larger. We even observe a semiconductor-metal transition in HgSe nanocrystals as the size is increased. The doping control with surface chemistry is then investigated. By using dipolar effects or oxidizing ligands, we show a doping control over several orders of magnitude. Thanks to these studies, we are able to propose a HgTe based device for detection at 2.5 µm, which structure allows to convert effectively the absorbed photons into an electrical current and to get a high signal over noise ratio. We get a photoresponse of 20 mA/W and a detectivity of 3 × 10 9 Jones

HgTe, the Most Tunable Colloidal Material: from the Strong Confinement Regime to THz Material

International audienceHgTe nanocrystals are extremely interesting materials to obtain a highly tunable absorption spectrum in the infrared range. Here, we discuss the two extreme cases of strongly confined and barely confined HgTe nanocrystals. We discuss the synthesis and optoelectronic properties of HgTe 2D nanoplatelets where the confinement energy can be as large as 1.5 eV. This material presents enhanced (mostly narrower) light emitting properties compared to spherical nanocrystals emitting at the same wavelength. Moreover, absorption spectra, majority carriers and time response can be tuned by carefully choosing the surface chemistry and applying a well-chosen gate bias. HgTe can also be used to explore the effect of vanishing confinement and to obtain quasi bulk properties with tunable absorption in the THz, up to 150 µm

Il y a 50 ans... la découverte d'Aï Khanoum : 1964-1978, fouilles de la Délégation archéologique française en Afghanistan (DAFA)

Plaquette éditée en hommage à Paul Bernard, directeur de la Délégation archéologique française en Afghanistan (1965-1980) et de la fouille d'Aï Khanoum (1965-1978)International audienc