Stage

  • (en anglais) All-Dielectric Metamaterials for Zero-Index-Photonic : Negative Index and Near-Zero Index Materials at Terahertz

    A partir de mars 2023

    Eric Akmansoy

    eric.akmansoy@universite-paris-saclay.fr - ‭01 70 27 05 29‬

    Département Photonique

    Stage

    M2 internship research proposal

    All-Dielectric Metamaterials for Zero-Index-Photonic  : Negative Index and Near-Zero Index Materials at Terahertz

    __________________

    General framework

    Metamaterials have opened a new field in physics and engineering. Indeed, these artificial structured materials give rise to unnatural fascinating phenomena such as negative index, sub-wavelength focusing and cloaking. Metamaterials also exhibit near-zero refractive index [1]. These open a broad range of applications, from the microwave to the optical frequency domain. Metamaterials have now evolved towards the implementation of optical components [2].

    We consider All-Dielectric Metamaterials (ADM) which are the promising alternative to metallic metamaterials, because they undergo no ohmic losses and consequently benefit of low energy dissipation and because they are of simple geometry [3]. They consist of high permittivity dielectric resonators involving Mie resonances. We have experimentally demonstrated negative effective permeability and/or permittivity by the means of all-dielectric metamaterials [4]. Previously, we have also demonstrated a negative index all-dielectric metamaterial [5].

    Metamaterials that exhibit Near-Zero Index metamaterials (NZI) have a large number of applications including wavefront engineering, directivity and gain enhancement of antennas, electromagnetic cloaking, phase matching for nonlinear applications, unidirectional transmission, defect waveguides, Zero-index Materials (ZIM) cavities, . . . [6]

    The main feature of Zero Index Materials is that the phase distribution of the EM field is nearly constant, because of the decoupling of the electric and the magnetic fields, that results in the “decoupling of the “spatial” (wavelength) and the “temporal” (frequency)”. [1] Zero Index Photonics has consequently fundamental and technological implications on different subfields of optics and nanophotonics. Antennas systems and optical components operating in the terahertz range are the targeted devices.

    Recently, we have numerically demonstrated a metadevice, namely, a metalens that focuses an incident plane wave and is less than one and a half wavelength thick. Its focal length is only a few wavelengths and the spot in the focal plane is diffraction-limited. [7]. We have also addressed the role of the coupling of the modes of Mie resonances in an all-dielectric metamaterial so as to achieve negative index and Near-Zero Index at terahertz frequencies [8].

    Work Plan

    During this M2 interbship, All-Dielectric Metamaterials will be numerically designed ; Negative Index and Near-Zero Index will be addressed. The All-Dielectric Metamaterials will also be characterized in the THz frequency range. In the first instance, our aim is to demonstrate near-zero index and negative index. Then antennas systems and various photonics components will be considered.

    This work takes place within the framework of the DisPonT ANR project. It gathers a group of scientists of different disciplines (chemists, material scientists and physicists) [9] which deals with All-Dielectric Metamaterials design, hight dielectric material fabrication, structuration and characterization [9, 10].

    ________________________

    Bibliography

    [1]  I. Liberal and N. Engheta, “Near-zero refractive index photonics,” Nature Photonics, vol. 11, pp. 149 EP –, 03 2017.

    [2]  N. I. Zheludev and Y. S. Kivshar, “From metamaterials to metadevices,” Nat Mater, vol. 11, pp. 917–924, 11 2012.

    [3]  S. Jahani and Z. Jacob, “All-dielectric metamaterials,” Nature Nanotechnology, vol. 11, pp. 23 EP –, 01 2016.

    [4]  T. Lepetit, E. Akmansoy, and J.-P. Ganne, “Experimental evidence of resonant effective permittivity in a dielectric metamaterial,” Journal of Applied Physics, vol. 109, no. 2, p. 023115, 2011.

    [5]  T. Lepetit, É. Akmansoy, and J.-P. Ganne, “Experimental measurement of negative index in an all-dielectric metamaterial,” Applied Physics Letters, vol. 95, no. 12, p. 121101, 2009.

    [6]  N. Shankhwar, Y. Kalra, Q. Li, and R. K. Sinha, “Zero-index metamaterial based all-dielectric nanoantenna,” AIP Advances, vol. 9, no. 3, p. 035115, 2019.

    [7]  F. Gaufillet, S. Marcellin, and E. Akmansoy, “Dielectric metamaterial-based gradient index lens in the terahertz frequency range,” IEEE J Sel Top Quant, vol. 10. 1109/JSTQE. 2016. 2633825, 2017.

    [8]  Akmansoy, Eric and Marcellin, Simon, “Negative index and mode coupling in all-dielectric metamaterials at terahertz frequencies,” EPJ Appl. Metamat., vol. 5, p. 10, 2018.

    [9]  C. Dupas, S. Guillemet-Fritsch, P.-M. Geffroy, T. Chartier, M. Baillergeau, J. Mangeney, J.-F. Roux, J.-P. Ganne, S. Marcellin, A. Degiron, and É. Akmansoy, “High permittivity processed SrTiO3 for metamaterials applications at terahertz frequencies,” Scientific Reports, vol. 8, no. 1, p. 15275, 2018

    [10] Djemmah, Djihad Amina and Geffroy, Pierre-Marie and Chartier, Thierry and Roux, Jean-François and Bouamrane, Fayçal and Akmansoy, Éric. "Processing High Permittivity TiO2 for All-Dielectric Metamaterials Applications at Terahertz Frequencies" , Proceedings of the Sixth International Symposium on Dielectric Materials and Applications (ISyDMA’6), pp. 177–183, 2022

     

    poursuite en thèse envisageable

  • (en anglais) Multiscale characterization of photovoltaic materials

    A partir de mars 2023

    Stéphane Collin

    stephane.collin@c2n.upsaclay.fr - +33 1 7027 0630

    Département Photonique

    Stage

    Context

    In the past years, photovoltaics (PV) became one of the cheapest sources of energy. 95% of commercial solar cells are made of silicon, and their lab-scale record efficiencies of 26.7 % are now close to the theoretical limit (29.4 %). Yet, expectations of both the society and the PV industry are still high, and most of the research efforts are now dedicated to pushing forward the efficiency of solar cells. Silicon-based tandem devices are the most-regarded solutions for next-generation photovoltaics. To keep low costs and preserve the silicon bottom cell, low-temperature deposition is mandatory for the top cell. Current options are polycrystalline, high-bandgap semiconductors like hybrid perovskites and inorganic Cu(In,Ga)(S,Se)2 -CIGS- or CdTe thin films, but they are still limited by both efficiency and/or stability issues that are hardly explained by current models. Further developments require a better understanding of the properties and limitations of low-cost thin-film materials. In particular, it is necessary to differentiate the properties of grain interiors and grain boundaries, and the macroscopic fluctuations that may occur in semiconductor alloys.

    Scientific project

    The goal of this project is to use and to combine cathodoluminescence and photoluminescence techniques to provide a multiscale analysis of materials and devices. Elementary processes and properties of bulk materials (doping levels, diffusion length, carrier lifetime, defect levels and densities...) and surfaces (surface recombination velocity, density of defects, surface charges…) will be determined quantitatively down to the nanometer scale, and then mapped on large surface areas and linked to the macroscopic properties of devices. A long-term objective is to use advanced computational methods for correlative data analysis, and simulation to build a realistic model of thin-film solar cells using the measured quantities.

    This internship will first focus on the unique cathodoluminescence (CL) tool available at C2N. Its basic principle is the following: a material is excited with an electron beam in a scanning electron microscope (SEM), providing a spatial resolution of 10 nm. Secondary electrons (SE) are collected to form an SEM image, and emitted photons (cathodoluminescence, CL) are collected simultaneously to acquire an hyperspectral image (luminescence spectrum at each point of the map). Time-resolved CL is also available to measure the luminescence decay after a pulsed excitation.

    The candidate will be first trained on the CL/TRCL tool. Then, she/he will use this technique to perform and analyze multiscale CL/TRCL mapping, with the goal to develop new methods to reveal the dynamics of carriers (lifetime, diffusion length, recombination velocities at interfaces...) and correlate these properties to the functional parameters of solar cells.

    The institute

    The candidate will work with several members of the sunlit team (C2N) and in close collaboration with the “Institut photovoltaïque d’Ile-de-France” (IPVF).

    Websites: https://sunlit-team.eu , https://www.c2n.universite-paris-saclay.fr/en , https://www.ipvf.fr

    Description of the CL setup and recent publications: https://sunlit-team.eu/resources/cl-and-trcl-tool/

    Profile: Student in M2 with a solid knowledge in semiconductor physics and optics.

    Possibility to continue with a PhD grant on multiscale characterization of PV materials in 2023.

    Send CV and motivation letter to stephane.collin@c2n.upsaclay.fr and  stefano.pirotta@c2n.upsaclay.fr

    poursuite en thèse envisageable

  • (en anglais) Multilayer epitaxial lift-off for low-cost III-V//Si tandem solar cells

    A partir de mars 2023

    Stéphane Collin

    stephane.collin@c2n.upsaclay.fr - +33 1 7027 0630

    Département Photonique

    Stage

    Scientific project

    Solar cells made of III-V materials present the best efficiencies among currently available technologies, up to 47% under concentration. Nevertheless, their cost is significantly higher than mainstream silicon modules. The major part of this cost, about 80% to 90%, lies in the III-V substrates necessary for the growth of monocrystalline materials with sufficient quality. The reuse or multi-use of GaAs substrates is currently the main obstacle to lower the cost of III-V solar cells.

    This project aims at developing of a novel device processing technique based on wet chemical etching and multi-epitaxy (several cells simultaneously). It will explore a new strategy to peel-off multiple layers selectively and one-by-one from a single substrate. It is based on an original "epitaxial-lift-off” approach, which will avoid the need of substrate reconditioning and reduces the growth dead-times of 10 different epitaxies to zero (pumping, degassing, annealing), resulting in a strong reduction of the cost of III-V solar cells.

    After a training to clean-room security and processes, the candidate will prepare an experimental setup and develop the multi-layer lift-off process. The short-term goal is to demonstrate the selective, remote-controlled, sequential etching and bonding of multiple III-V layers from a single substrate (large-surface, layer-by-layer take-and-place process). The final goal of the internship will be to use this technique to fabricate a first proof-of-concept device, and to combine this new process with our recent breakthrough in the fabrication of ultrathin GaAs solar cells [1,2].

    Profile

    We are looking for a candidate in M2 or 3rd year of the engineering cycle, with a solid knowledge in solid-state physics, condensed-matter physics and/or physical chemistry.  The candidate must show good project management skills, for the development of technological procedures involving numerous parameters. Fluent communication skills in English are required for an international team (SunLit) working as well as regular presentation of work progress in internal meetings. The candidate is expected to be able to work independently and suggest innovative solutions to reach the project objectives, and to be able to collaborate with other members of the team.

    Possibility to continue with a PhD grant on high-efficiency PV in 2023.

    The institute

    The project is part of the IPVF scientific program on low-cost III-V solar cells, it is hosted by the SunLit team (C2N, CNRS) composed of both CNRS and IPVF researchers:

    More information on the SUNLIT Team: https://sunlit-team.eu

    C2N laboratory (CNRS, University Paris-Saclay): https://www.c2n.universite-paris-saclay.fr/en

    IPVF: https://www.ipvf.fr, and https://www.linkedin.com/company/ipvf-institute/mycompany/

    Send CV and motivation letter to: jeronimo.buencuerpo@ipvf.fr,  stephane.collin@c2n.upsaclay.fr

    References:

    [1] H.-L. Chen et al., A 19.9%-efficient ultrathin solar cell based on a 205-nm-thick GaAs absorber and a silver nanostructured back mirror. Nature Energy 4, 761-767, 2019.

    [2] I. Massiot, A. Cattoni, S. Collin. Progress and prospects for ultrathin solar cells. Nature Energy 5, 959-972, 2020.

    poursuite en thèse envisageable

  • (en anglais) New assessment of the efficiency limits in solar photovoltaics

    A partir de mars 2023

    Stéphane Collin

    stephane.collin@c2n.upsaclay.fr - +33 1 7027 0630

    Département Photonique

    Stage

    Context

    Solar photovoltaics should play a major role to fulfil the goals set for the energy transition and Paris Agreement. In the sustainable development scenarios of the International Energy Agency (IEA), the share of photovoltaics in electricity generation is expected to increase from 6% in 2017 to 22% in 2030. Nowadays, most commercial photovoltaic modules are made of silicon (Si) wafers with thicknesses of more than 150 µm, an average conversion efficiency of about 20%, and record solar cells up to 26.7%. To accelerate the energy transition, it is necessary to further increase the conversion efficiency of solar cells, and to reduce their cost.

    Ultrathin solar cells with thicknesses at least 10 times lower than conventional solar cells could have the unique potential to efficiently convert solar energy into electricity while enabling material savings, shorter deposition times and improved carrier collection. In 2019, we have achieved an important milestone by trapping sunlight efficiently in a GaAs solar cell as thin as 200 nm, using a nanostructured back mirror. This new architecture is based on multi-resonant absorption and led to a record efficiency of nearly 20% [1]. In a recent review published in Nature Energy [2], we have highlighted the very high potential of ultrathin solar cells, the challenges to overcome to get closer to the theoretical limits, and the most promising research directions.

    Scientific project

    In this internship, we propose to reassess the theoretical limits of silicon solar cells, and to show that the well-known Shockley-Queisser limit of single-junction solar cells should be revisited with an appropriate light-trapping model (the absorption upper bound). The starting point is the following: the well-known fundamental efficiency limit of silicon solar cells is 29.4% and requires a thickness of 100 µm [3]. However, it is based on an absorption model that assumes Lambertian scattering, which is not the optimal light-trapping scheme. Recently, we have developed a new absorption model based on multi-resonant absorption, and we have derived analytical formulas for the absorption upper bounds [4]. This work paves the way towards a reassessment of the fundamental efficiency limit of silicon solar cells, expected to be above 30% for much thinner cells (a few tens of µm). Since the vast majority of installed solar panels are made of silicon, the results of this study will have an important impact in the field.

    This work will be focused on the development of theoretical models and the use of simulation tools. The short-term objective is to combine multi-resonant absorption models and transport equations of charge carriers in a silicon solar cell. The model will be first compared to previous publications, and then it will be used to derive the new fundamental efficiency limits of silicon solar cells based on the absorption upper bound. The mid-term objective is to design ultrathin solar cells that get close to the theoretical limits, and to explore the tradeoffs that constrain the efficiency of actual devices.

    The team

    This work will be done in close collaboration between the ​C2N (​SUNLIT Team​) and the ​IPVF both located on Paris-Saclay campus in Palaiseau (one block away). More information on the SUNLIT Team: https://sunlit-team.eu

    Profile: Student in M2 with a solid knowledge in semiconductor physics and optics.

    Possibility to continue with a PhD grant on ultrathin, high-efficiency solar cells in 2023.

    Send CV and motivation letter to: stephane.collin@c2n.upsaclay.fr

    References:

    [1] H.-L. Chen et al., A 19.9%-efficient ultrathin solar cell based on a 205-nm-thick GaAs absorber and a silver nanostructured back mirror. Nature Energy 4, 761-767, 2019.

    [2] I. Massiot, A. Cattoni, S. Collin. Progress and prospects for ultrathin solar cells. Nature Energy 5, 959-972, 2020.

    [3] T. Niewelt et al., Reassessment of the intrinsic bulk recombination in crystalline silicon. Solar Energy Materials and Solar Cells 235, 111467 (2022).

    [4] S. Collin and M. Giteau, in preparation (2022).

    poursuite en thèse envisageable

  • (en anglais) Surface texturing process for the lateral epitaxial growth of AlGaAs/Si photovoltaic tandem cell

    A partir de mars 2023

    Charles Renard

    charles.renard@c2n.upsaclay.fr - 01 70 27 03 46

    Département Materiaux

    Stage

    CV and motivation letter to : Charles Renard (charles.renard@c2n.upsaclay.fr)
    Phone / e-mail : 01 70 27 03 46 / charles.renard@c2n.upsaclay.fr

    Context of the research project and motivations
    SEEDs team of C2N have developed an innovative strategy for the integration of III-V materials on silicon. The latter is based on lateral epitaxial growth from nano-seeds formed in an ultra-thin silica layer (less than 2 nm thick) covering the silicon substrate. With this process we have demonstrated: i)
    the perfect integration of GaAs crystals of micrometric sizes dispersed on Si without any structural or electrical detrimental defect [1,2], ii) the very good electrical connection not only between the GaAs microcrystals and the Si substrate, but also through the GaAs/SiO2 /Si stack by tunnel effect [2].
    The next step is now the realization of an AlGaAs/Si tandem photovoltaic (PV) cell demonstrator. For this, we need to develop a low-cost technological process of ordered nanostructuring of silica from lithography by nanospheres which can be easily extended to a large surface. Such process will ensure very low III-V material requirement and no use of III-V or Ge substrate helping thus maintain low-cost.

    Objectives and description of the internship (3-6 months)
    We propose to develop a process to minimize the cost of the localization process of nanometric growth seeds, namely nanosphere lithography (NSL). The NSL technique is based on the self-organization [3] of cheap, commercially available polystyrene (or silica) beads. Thanks to the use of simple synthesis processes, one can thus easily produce by spin-coating single or double layers of beads on Si substrates.
    By using different diameters of beads, one can easily adjust the distance between the apertures (in the range 20-1000 nm), and obtain small apertures between the beads (up to 20 nm). These openings will then be used as a mask to obtain the nanometric Si seeds necessary for the localized epitaxy of the AlGaAs μ-crystals. With this technique, we therefore propose to produce hexagonal patterns of nanometric seeds through a very thin layer of SiO2 . Once this method of nanostructuring by NSL has been mastered, we will continue to set up the basic bricks for the realization of the PN junction in the crystals of AlGaAs for the realization of a tandem photovoltaic cell on Si.

    Profile
    M2 or 3rd year of the engineering cycle, with a solid knowledge in materials science, condensed-matter physics and/or physical chemistry. The candidate must show ability to work in a clean room and strong taste for experimentation and microstructural analysis Materials. The candidate is expected to be able to work independently, suggest innovative solutions, and to collaborate with other international members of the SEEDs team. English communication skills are required for regular presentation of work progress in internal meetings. Possibility to continue with a PhD grant with ANR (Agence Nationale de la Recherche) funding

    Laboratory and hosting team
    This internship is part of an ANR project (HELLO_PV) dedicated to photovoltaic bringing together
    C2N, IPVF and GEEPs laboratory, and is hosted by the SEEDs team (C2N, CNRS / Université Paris
    Saclay) of materials department (http://seeds.c2n.universite-paris-saclay.fr/en/research/)


    Références :
    [1] Renard C., et al., Dislocation and antiphase domain free microscale GaAs crystals grown on SiO2 from (001) Si nano-areas Applied Physics Letters, vol. 102, p. 191915, 2013
    [2] Renard C., et al., High current density GaAs/Si rectifying heterojunction by defect free Epitaxial Lateral overgrowth on Tunnel Oxide from nano-seed, Scientific Reports, vol. 6, p. 25328, 2016 www.nature.com/articles/srep25328
    [3] D. Gogel et al., Plasma modification of nanosphere lithography masks made of polystyrene beads, J. Optoelectronics and Advanced Materials, Vol. 12, No. 3, March 2010, p. 740 – 744

     

  • (en anglais) All-Dielectric Metamaterials for Zero-Index-Photonics : Negative Index and Near-Zero Index Materials at Terahertz

    A partir de mars 2023

    Éric Akmansoy

    eric.akmansoy@universite-paris-saclay.fr - ‭01 70 27 05 29‬

    Département Photonique

    Stage

    General framework

    Metamaterials have opened a new field in physics and engineering. Indeed, these artificial struc- tured materials give rise to unnatural fascinating phenomena such as negative index, sub-wavelength focusing and cloaking. Metamaterials also exhibit near-zero refractive index [1]. These open a broad range of applications, from the microwave to the optical frequency domain. Metamaterials have now evolved towards the implementation of optical components [2].

    We consider All-Dielectric Metamaterials (ADM) which are the promising alternative to me- tallic metamaterials, because they undergo no ohmic losses and consequently benefit of low energy dissipation and because they are of simple geometry [3]. They consist of high permittivity dielec- tric resonators involving Mie resonances. We have experimentally demonstrated negative effective permeability and/or permittivity by the means of all-dielectric metamaterials [4]. Previously, we have also demonstrated a negative index all-dielectric metamaterial [5].

    Metamaterials that exhibit Near-Zero Index metamaterials (NZI) have a large number of ap- plications including wavefront engineering, directivity and gain enhancement of antennas, electro- magnetic cloaking, phase matching for nonlinear applications, unidirectional transmission, defect waveguides, Zero-index Materials (ZIM) cavities, . . . [6]

    The main feature of Zero Index Materials is that the phase distribution of the EM field is nearly constant, because of the decoupling of the electric and the magnetic fields, that results in the “decoupling of the “spatial” (wavelength) and the “temporal” (frequency)”. [1] Zero Index Photonics has consequently fundamental and technological implications on different subfields of optics and nanophotonics. Antennas systems and optical components operating in the terahertz range are the targeted devices.

    Recently, we have numerically demonstrated a metadevice, namely, a metalens that focuses an incident plane wave and is less than one and a half wavelength thick. Its focal length is only a few wavelengths and the spot in the focal plane is diffraction-limited. [7]. We have also addressed the role of the coupling of the modes of Mie resonances in an all-dielectric metamaterial so as to achieve negative index and Near-Zero Index at terahertz frequencies [8].

     

    Work Plan

    During this internship, All-Dielectric Metamaterials will be numerically designed; Negative Index and Near-Zero Index will be addressed. The All-Dielectric Metamaterials will also be cha- racterized in the THz frequency range. The student can also get involved in the fabrication processes. In the first instance, our aim is to demonstrate near-zero index and negative index. Then antennas systems and various photonics components will be considered.

    This work takes place within the framework of a group of scientists of different disciplines (che- mists, material scientists and physicists) [9] which deals with All-Dielectric Metamaterials design, hight dielectric material fabrication, structuration and characterization [9, 10].

    Bibliography

    1. [1]  I. Liberal and N. Engheta, “Near-zero refractive index photonics,” Nature Photonics, vol. 11, pp. 149 EP –, 03 2017.

    2. [2]  N. I. Zheludev and Y. S. Kivshar, “From metamaterials to metadevices,” Nat Mater, vol. 11, pp. 917–924, 11 2012.

    3. [3]  S. Jahani and Z. Jacob, “All-dielectric metamaterials,” Nature Nanotechnology, vol. 11, pp. 23 EP –, 01 2016.

    4. [4]  T. Lepetit, E. Akmansoy, and J.-P. Ganne, “Experimental evidence of resonant effective permittivity in a dielectric metamaterial,” Journal of Applied Physics, vol. 109, no. 2, p. 023115, 2011.

    5. [5]  T. Lepetit, É. Akmansoy, and J.-P. Ganne, “Experimental measurement of negative index in an all- dielectric metamaterial,” Applied Physics Letters, vol. 95, no. 12, p. 121101, 2009.

    6. [6]  N. Shankhwar, Y. Kalra, Q. Li, and R. K. Sinha, “Zero-index metamaterial based all-dielectric nanoan- tenna,” AIP Advances, vol. 9, no. 3, p. 035115, 2019.

    7. [7]  F. Gaufillet, S. Marcellin, and E. Akmansoy, “Dielectric metamaterial-based gradient index lens in the terahertz frequency range,” IEEE J Sel Top Quant, vol. 10. 1109/JSTQE. 2016. 2633825, 2017.

    8. [8]  Akmansoy, Eric and Marcellin, Simon, “Negative index and mode coupling in all-dielectric metamaterials at terahertz frequencies,” EPJ Appl. Metamat., vol. 5, p. 10, 2018.

    9. [9]  C. Dupas, S. Guillemet-Fritsch, P.-M. Geffroy, T. Chartier, M. Baillergeau, J. Mangeney, J.-F. Roux, J.-P. Ganne, S. Marcellin, A. Degiron, and É. Akmansoy, “High permittivity processed SrTiO3 for me- tamaterials applications at terahertz frequencies,” Scientific Reports, vol. 8, no. 1, p. 15275, 2018.

    10. Djemmah, D.A., Geffroy, PM., Chartier, T., Roux, JF., Bouamrane, F., Akmansoy, É. (2022). Processing High Permittivity TiO2 for All-Dielectric Metamaterials Applications at Terahertz Frequencies. In: Vaseashta, A., Achour, M.E., Mabrouki, M., Fasquelle, D., Tachafine, A. (eds) Proceedings of the Sixth International Symposium on Dielectric Materials and Applications (ISyDMA’6). Springer, Cham. https://doi.org/10.1007/978-3-031-11397-0_15

     

     

    poursuite en thèse envisageable

  • Étude détaillée et optimisation des contacts métalliques sur GaAs Nouvel développement technologique pour les récepteurs sensibles

    A partir de décembre 2022

    Yong JIN

    yong.jin@c2n.upsaclay.fr - 01 70 2 7 06 25

    Département Nanoelectronique

    Stage

    Contexte du projet

    Depuis plus 15 ans, le LERMA-Observatoire de Paris associé avec le C2N (Centre de Nanosciences et de Nanotechnologies) travaillent sur la conception et la réalisation des composants électroniques à base des diodes Schottky sur GaAs afin de construire des dispositifs THz sensibles pour la radioastronomie. Récemment, le LERMA-C2N a développé et fabriqué les sources (multiplicateurs de fréquence) à 300GHz et 600GHz, ainsi que le détecteur 1.2THz (mélangeur de fréquence), qui ont été installés sur un radiotélescope Submillimeter Wave Instrument (SWI) de la mission Jupiter ICy moon Explorer (JUICE) de l'ESA, qui sera lancée en avril 2023 pour étudier Jupiter et ses lunes galiléennes. Les performances des mélangeurs de fréquences à 600Hz et 1.2THz fabriqués par le LERMA-C2N ont défini un nouvel état de l'art dans le monde des détecteurs hétérodynes à ces fréquences. Pour conserver sa position de leader et répondre aux nouvelles demandes des agences spatiales (CNES, ESA, NASA...), le LERMA intente de repousser encore plus loin les limites de la technologie de fabrication pour atteindre des fréquences aussi élevées que 5THz. Pour y parvenir, chaque étape de fabrication doit être parfaitement optimisée et contrôlée. En particulier, les contacts métal-semiconducteur sont les points clés de tous les dispositifs électroniques, et leur préparation et caractérisation constituent les efforts majeurs dans la fabrication des circuits. La compréhension des mécanismes et l'optimisation des conditions expérimentales permettant la réalisation de contacts stables et à faible résistance sont essentielles pour obtenir des circuits intégrés performants et fiables à haute fréquence.

    Objectifs

    L'objectif de ce stage est de développer le procédé de fabrication permettant la réalisation de contacts métalliques stables et à faible résistance sur GaAs. Le développement du procédé sera réalisé dans la centrale de technologie du C2N sur des équipements de pointe pour la micro et la nanofabrication. Ce travail permettra à l'étudiant d'acquérir une grande expérience en nanotechnologie et en fabrication de dispositifs (lithographie optique et/ou par faisceau d'électrons, dépôt de couches métalliques minces, gravure sèche et humide et autres outils de salle blanche), ainsi qu'en caractérisation des circuits hyperfréquences.

    Ce travail s’intègre au sein des projets R&T CNES et PEPR pour le développement de récepteurs très haute fréquence pour l'astronomie. Ce stage pourra se poursuivre par une thèse de doctorat en collaboration entre le LERMA, le C2N et le CNES (demande de subvention à faire).

    Profil du candidat

    Le candidat doit être motivé, autonome, rigoureux et avoir le bon sens de la communication. Niveau d'études requis : Master 1 ou diplôme équivalent en ingénierie. Connaissances en science des matériaux, physique des solides ou nano/microfabrication. Une bonne connaissance de l'anglais est attendue.

    Personne à contacter : Pour postuler, veuillez envoyer votre lettre de motivation, votre CV et vos lettres de recommandation (facultatives) à l'adresse suivante :

    Dr. Lina GATILOVA (LERMA, Observatoire de Paris, Paris), lina.gatilova@obspm.fr

    Dr. Yong JIN (C2N, CNRS, Palaiseau), yong.jin@c2n.upsaclay.fr

  • (en anglais) Dynamics and photonic computing with coupled microlaser neurons

    A partir de novembre 2022

    Sylvain Barbay

    sylvain.barbay@c2n.upsaclay.fr - 01 70 27 04 51

    Département Photonique

    Stage

    Neuromorphic photonics is an expanding field of research at the heart of recent progresses in analog computation and machine learning. Its goal is to investigate new ways to process optical information or to compute using brain-inspired physical concepts. We propose to investigate the physics and applications of coupled spiking photonic nodes implementing artificial spiking neural networks. Each node (optical neuron) is materialized by a micropillar laser with integrated saturable absorber, whose neuromimetic properties have already been explored in the team [1]. In neurons, information is coded with spikes (electrical pulses) which are excited in an all-or-none fashion provided input stimuli to the neuron soma exceed a given threshold. This generic property is called excitability and has been  demonstrated in micropillar lasers with optical spikes. Though, the optical spikes emitted by these latter are more than one millions times shorter in duration than biological action potentials. Hence, photonic neurons could in principle be interesting to build ultrafast artificial neural networks with low power consumption.

    The objective of the internship will be to take part to the projects developed in the group to fabricate and study neuromorphic architectures, understand the physics involved in the dynamics of these coupled microlasers and demonstrate ultrafast analog computation. The work will mainly involve experimental and modeling activites, with nanofabrication aspects. The internship will take place at the C2N (Palaiseau) which hosts a first-class nanofabrication facility.
    The applicant should have a background in physics, optics, laser physics, semiconductor physics, and possibly semiconductor lasers and/or nonlinear dynamics and/or machine learning. The internship can be followed by a PhD.

    References:

    [1] Microlasers for neuromorphic computing, Photoniques 104, 26-29 (2020). https://doi.org/10.1051/photon/202010426

    poursuite en thèse envisageable

  • Nouveaux films getter pour l’encapsulation sous vide de micro-dispositifs Elaboration et caractérisation physicochimique, structurale, électrique et optique

    A partir de octobre 2022

    Johan Moulin

    johan.moulin@universite-paris-saclay.fr - 01 70 27 05 25

    Département Microsyst

    Stage

    Le département Microsystèmes et Nanobiofluidique du C2N conçoit, élabore et teste des micro-dispositifs électromécaniques et électromagnétiques pour le médical, l'aéronautique, la récupération d’énergie et le domaine des semiconducteurs et développe des technologies pour le packaging et le management thermique de microdispositifs. Les travaux de recherche s’appuient sur la Centrale de Micro- Nano-fabrication du C2N (2800 m2 de salles blanches), la plus grande centrale académique en France.
    De nombreux microdispositifs nécessitent d’être encapsulés sous vide pour obtenir des performances élevées. Ceci est réalisé par un scellement hautement hermétique d’un capot et l’intégration de matériaux getter très réactifs et donc capables d’absorber les molécules gazeuses présentes dans la microcavité de l’encapsulation. En partenariat avec le milieu industriel, le département étudie depuis une dizaine d’années des nouveaux matériaux getter très divers pour cette application. Le challenge est de trouver des matériaux permettant d’obtenir et de maintenir un bon niveau de vide sur une durée de 10 ans ou plus. Les alliages usuels à base de métaux de transition (Zr, V, Co, Fe, ...) ont une bonne capacité de piégeage des gaz réactifs mais présentent une faible sorption irréversible de l'hydrogène, ce qui limite le niveau de vide atteignable.
    L'objectif du stage consiste donc, dans le cadre d'un projet de l’Agence Nationale de la Recherche (ANR) en collaboration avec le CEMHTI d'Orléans pour l'analyse des matériaux par faisceaux d'ions, à étudier les propriétés de sorption de nouveaux alliages getter à base d'yttrium. Cet élément a la particularité de former facilement des hydrures stables, ce qui est très recherché pour la sorption d'hydrogène.

    Il s'agira donc de contribuer :
    - à l'élaboration de films minces d’alliages ternaires de métaux de transition et d'yttrium
    - à la caractérisation de la structure, la morphologie et les propriétés électriques, mécaniques et/ou optiques de ces alliages en fonction de la température ;
    - à la caractérisation de la sorption des éléments légers dans ces alliages à l'aide des mesures ci-dessus, d'analyses par faisceaux d’ions (RBS, NRA, ERDA) de la composition de la composition de surface et de volume des films et de mesures de la cinétique de sorption de gaz sous ultravide ;
    - à l’analyse des résultats à partir des mécanismes physico-chimiques mis en jeu.

    Ces travaux pourront être poursuivis en thèse en partenariat avec la société Lynred

    Toutes les informations dans le document joint

    poursuite en thèse envisageable

  • (en anglais) Optoelectronic devices enabled by vacuum field photons

    A partir de octobre 2022

    Raffaele Colombelli

    raffaele.colombelli@universite-paris-saclay.fr - 01 70 27 06 29

    Département Photonique

    Stage

    Optoelectronic devices are an integral part of our daily life and are expected to play an increasingly important role in the future. As the basic operating principles of optoelectronic devices are known, their improvement – while important – is often incremental. Finding new avenues to implement novel functionalities is a key challenge: cavity quantum electrodynamics (QED) promises new approaches to innovate such devices by exploiting the quantum mechanical principles of strong (SC) and ultra-strong (USC) light-matter coupling regimes [1] in microcavities.

    When the light-matter interaction becomes comparable to the unperturbed electronic transition energy, one reaches the so called ultra-strong (USC) coupling regime. The sole presence of the cavity can induce modifications of ground and excited states, and therefore of the device electronic behavior. Such effects have been observed in several systems like organic conductors [2] or 2D electron gas  [3], laying the grounds for the field of polaritonic chemistry  [4].

    The project's goal is is to elucidate the direct influence of the electro-magnetic vacuum on the electronic energy levels and the electronic transport properties in semiconductor optoelectronic quantum devices.  The research will focus on optoelectronic devices relying on so-called intersubband transitions between quantum-confined electronic states in semiconductor quantum wells (QWs). Such transitions are the building blocks of mid-infrared/THz quantum devices (quantum cascade lasers, infrared QW detector).

    These devices perfectly suit the exploration of new phenomena where cavity electrodynamics and electronic transport both play a fundamental role.  For instance the structure reported in the figure on the side is an ideal practical realization of a photoconductor device that can exhibit vacuum-field assisted transport. When real photons are absorbed, a photocurrent is generated as electrons are promoted in the continuum: it behaves as a detector. When operating as a detector in strong coupling, selective excitation of the polaritonic states permits access to their resonant extraction into an electric current, as recently demonstrated by the host team [5] [6]. In USC in the dark, this additional channel (orange arrow) is activated by virtual photons.

    The internship we propose is experimental, and aims at measuring the effect of a cavity on the electronic transport in this system. The active region will be embedded in metal-metal ribbon cavities that confine the electromagnetic field inside the semiconductor active region (see figure below), and current-voltage measurements will be performed as a function of the temperature in a closed-cycle cryostat (from 4K to 200K) AND as a function of the cavity energy. This latter parameter is crucial as it affects the details of the light-matter interaction. An important part of the internship will be devoted to setting up the measurement system (the equipment is already in place), mostly in terms of automation with a PC via programming in python. This will permit to focus on the science, and optimize the system in order to maximize the light-matter interaction and the expected effect on the transport.

    Methods and techniques: Quantum design of semiconductor heterostructure, python instrument control, optoelectronic characterization (mid-IR Fourier transform spectroscopy, current-voltage measurement).

    poursuite en thèse envisageable

  • (en anglais) Novel Mid-InfraRed polaritonic architectures

    A partir de octobre 2022

    Jean-Michel Manceau

    jean-michel.manceau@universite-paris-saclay.fr - 01 70 27 06 73

    Département Photonique

    Stage

    Non-equilibrium Bose-Einstein condensation of exciton-polaritons have become a vast playground for fascinating phenomena previously reserved to ultracold atomic gases. In particular, it has lead to the demonstration of superfluidity, hydrodynamic soliton nucleation, topological lasing and non-Hermitian effects. In these polaritonic systems the fundamental energy scale is intrinsically fixed by the interband transition of the underlying material, constrained to the VIS/Near-IR range, limiting flexibility and also the magnitude of the Rabi
    splitting. Conversely, the transition energy of intersubband (ISB) polaritons in doped semiconductor quantum well (QW) structures can be freely tuned by varying the QW width and doping to reach the mid-IR and Far-IR range of the electromagnetic spectrum. As their excitonic counter-part, it has been predicted that they can show exotic quantum behavior such as final state stimulation and condensation. This would open interesting perspectives of a condensate operating at much lower energy scale and interacting with a 2D gas of electrons to form Fermi-Bose mixtures.

    Our team has made major progresses towards that goal in the recent years. Starting with dispersion engineering [1], we developed a clear roadmap towards condensation [2] and confirmed the existence of a spontaneous process based on ISB polariton - LO phonon scattering [3]. More recently, in the frame of an international collaboration, we demonstrated for the first time polariton-polariton interaction in the regime of final state stimulation (see figure) [4]. In this pump-probe experiment, we have shown an amplification process ocurring on an ultrafast time scale; this is the key ingredient towards condensation. We further developped a numerical tools to simulate such experiment and investigate in details the key parameters behind this amplification process.

    This internship aims at establishing the fundational bricks for the demonstration of ISB polaritons condensation. In particular we aim at developing novel polariton architectures to either increase the polaritonic non-linearities or the scatering rate. Prior to the internship, several QW structures will be designed and grown by our partners. The first task of the candidate will be to characterize the spectral absorption of the structure as function of the temperature (from 300 K down to 4 K) using the existing experimental apparatus. The candidate will then numerically design the microcavities that will host the strong coupling regime. The fabrication of the devices will be led in C2N cleanroom by the supervisor and she/he will be invited to follow the different steps of the process. The candidate will then perform the optical characterization of the polaritonic band-structure and extract several key parameters. Finally, the candidate will use an in-house numerical code to simulate the polaritons scattering dynamic and amplification process within the novel polaritonic architectures that she/he has characterized earlier on.

    The project offers a global view of the different activities led in our team from the numerical design, the fabrication in cleanroom and the optical characterization. Furthermore and if time allows, the candidate will also have the opportunity to contribute to the implementation of a pump-probe experiment based on an ultrafast laser chain recently purchased. This will be the key tool for a potential PhD thesis on ISB polariton condensation.

    [1] J.-M. Manceau et al., Mid-Infrared Intersubband Polaritons in Dispersive Metal-Insulator-Metal Resonators, Appl. Phys. Lett. 105, 8 (2014).
    [2] R. Colombelli and J.-M. Manceau, Perspectives for Intersubband Polariton Lasers, Phys. Rev. X 5, 1 (2015).
    [3] J.-M. Manceau et al., Resonant Intersubband Polariton-LO Phonon Scattering in an Optically Pumped Polaritonic Device, Appl. Phys. Lett. 112, 19 (2018).
    [4] M. Knorr, J.-M. Manceau et al., Intersubband Polariton-Polariton Scattering in a Dispersive Microcavity, Phys. Rev. Lett. 128, 247401 (2022).


    Methods and techniques: Optical characterization of the QW at cryogenic temperatures (FTIR absorption); EM
    numerical modelling of the microcavities; Optical characterization of the polaritonic band-structure (angle-resolved
    FTIR spectroscopy); Numerical modelling of the polaritons scattering dynamic and amplification.

    poursuite en thèse envisageable