C. Seassal

Ecole Centrale de Lyon, Rhône-Alpes, France

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Publications (201)293.45 Total impact

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    ABSTRACT: The effects resulting from the introduction of a controlled perturbation in a single pattern membrane on its absorption are first studied and then analyzed on the basis of band folding considerations. The interest of this approach for photovoltaic applications is finally demonstrated by overcoming the integrated absorption of an optimized single pattern membrane through the introduction of a proper pseudo disordered perturbation.
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    ABSTRACT: We investigate the specific optical regime occurring at short wavelengths, in the high absorption regime, in silicon thin-films patterned by periodically arranged nano-holes. Near-field scanning optical microscopy indicates that the incoming light is coupled to vertically channelling modes. Optical modelling and simulations show that the light, travelling inside the low-index regions, is absorbed at the direct vicinity of the nano-holes sidewalls. This channelling regime should be taken into account for light management in optoelectronic devices.
    Applied Physics Letters 01/2014; 104(5):-. · 3.79 Impact Factor
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    ABSTRACT: A 2-D photonic crystal was integrated experimentally into a thin-film crystalline-silicon solar cell of 1-{\mu}m thickness, after numerical optimization maximizing light absorption in the active material. The photonic crystal boosted the short-circuit current of the cell, but it also damaged its open-circuit voltage and fill factor, which led to an overall decrease in performances. Comparisons between modeled and actual optical behaviors of the cell, and between ideal and actual morphologies, show the global robustness of the nanostructure to experimental deviations, but its particular sensitivity to the conformality of the top coatings and the spread in pattern dimensions, which should not be neglected in the optical model. As for the electrical behavior, the measured internal quantum efficiency shows the strong parasitic absorptions from the transparent conductive oxide and from the back-reflector, as well as the negative impact of the nanopattern on surface passivation. Our exemplifying case, thus, illustrates and experimentally confirms two recommendations for future integration of surface nanostructures for light trapping purposes: 1) the necessity to optimize absorption not for the total stack but for the single active material, and 2) the necessity to avoid damage to the active material by pattern etching.
    IEEE Journal of Photovoltaics 12/2013; 4(1).
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    ABSTRACT: The aim of the study is to develop ultra-compact structures enabling an efficient conversion of single high energy photon (UV) to two lower energy photons (IR). The proposed structure combines rare-earths doped thin layer allowing the down-conversion process with a photonic crystal (PhC), in order to control and enhance the down-conversion using optical resonances. On the top of the rare-earths doped layer, a silicon nitride (SiN) 2D planar PhC is synthesized. For that, SiN is first deposited by PECVD. After holographic lithography and reactive ion etching, a periodic square lattice of holes is generated on the SiN layer. The PhC topographical parameters as well as the layers thickness are optimized using Finite-Difference-Time-Domain simulations. The design and realization of such PhC-assisted down-converter structures is presented. Optical simulations demonstrate that the PhC leads to the establishment of resonant modes located in the underneath doped layer, allowing a drastic enhancement of the absorption of the rare-earth ions without disturbing the transmission in the visible and near-IR parts of the spectrum, hence demonstrating the relevance of such an approach.
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    ABSTRACT: The positive effects of various perturbations introduced in a bidimensional photonic-crystal patterned membrane on its integrated absorption are investigated numerically and theoretically. Two phenomena responsible for the enhanced absorption observed are identified: an increase of the spectral density of modes, obtained thanks to folding mechanisms in the reciprocal lattice, and a better coupling of the modes with the incident light. By introducing a proper pseudodisordered pattern, we show that those two effects can be exploited so as to overcome the integrated absorption obtained for an optimized and single pattern unit cell photonic crystal.
    Physical Review A 11/2013; 88(5):053835. · 3.04 Impact Factor
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    ABSTRACT: Mixed photonic crystals (PCs), the photonic equivalent of semiconductor alloys, are ideal for use in investigating various phenomena occurring in disordered photonic systems. In the present study we fabricated highly disordered two-dimensional PCs, using a wafer-bonded InAsP/InP multiple-quantum-well slab, and examined the resultant photonic resonant modes by determining the spectrally and spatially resolved emission properties. We observed that new localized photon modes formed in the disordered PCs, which are in good contrast to the spatially extended band-edge modes associated with PCs having translational symmetry. Computer simulations confirmed the existence of such localized photon modes in the disordered PC structure.
    Physical Review A 08/2013; 88(2):023804. · 3.04 Impact Factor
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    ABSTRACT: In this paper, we present the design, analysis, and experimental results on the integration of 2D photonic crystals in thin film photovoltaic solar cells based on hydrogenated amorphous silicon. We introduce an analytical approach based on time domain coupled mode theory to investigate the impact of the photon lifetime and anisotropy of the optical resonances on the absorption efficiency. Specific design rules are derived from this analysis. We also show that, due to the specific properties of the photonic crystal resonances, the angular acceptance of such solar cells is particularly high. Rigorous Coupled Wave Analysis simulations show that the absorption in the a-Si:H active layers, integrated from 300 to 750nm, is only decreased from 65.7% to 60% while the incidence angle is increased from 0 to 55°. Experimental results confirm the stability of the incident light absorption in the patterned stack, for angles of incidence up to 50°.
    Optics Express 05/2013; 21(S3):A515-A527. · 3.55 Impact Factor
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    ABSTRACT: We report on a new type of photonic crystal laser structure, nano stepping-stones (NSSs), composed of a linear (or one-dimensional) chain of equally spaced discrete InAsP/InP multiple-quantum-well nanorods bonded onto a fused silica substrate. When optically pumped, the NSSs lased in a single band-edge mode with the polarization perpendicular to the direction along the NSSs. The cavity quality factor estimated from numerical simulations exceeded 104, and the measured threshold pump power density was as small as 285W/cm2. Detailed emission spectra analyses confirmed that the lasing occurred at a photonic band-edge.
    Applied Physics Express 04/2013; 6:042703. · 2.73 Impact Factor
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    ABSTRACT: In silicon-based solar cells, a substantial part of the energy losses is related to the charge carriers thermalization in the UV-blue range and the week carriers collection at these wavelenghts. To avoid this issue, we introduce a new concept which combines a rare-earths doped thin layer with a photonic crystal (PC) layer, allowing an efficient conversion from UV-blue photons to near-IR photons. We report on the feasibility of such a nanostructured down-converter module using an active rare-earth doped CaYAlO4 thin layer and a silicon nitride PC on top. By means of optical numerical simulations, the promising potentialities of the concept are demonstrated. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
    Proc SPIE 03/2013;
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    ABSTRACT: The periodic patterning of the optical medium achieved through photonic crystal membranes (PCMs) can be employed for controlling the resonant coupling of external radiation continuum to above-the-light-line flat edges of the folded band structure in strongly corrugated waveguides, resulting in high reflectivity for an efficient quasi-3D light harnessing. Recently, vertical-cavity surface-emitting lasers (VCSELs) emitting in C-band using a double set of one-dimensional Si/SiO2 photonic crystals as compact, flexible, and power efficient mirrors have been realized within a mass-scale fabrication paradigm by employing standard 200-mm microelectronics pilot lines. Conceived as the basic building block for photonics-on-silicon back-end integration of group III-V laser microsources, the extreme flexibility of the novel photonic architecture enables to perform a tailored modal selection of the optical cavity, including polarization and far-field control. It also offers a wide range of functionality, such as on-chip optical routing and a variety of efficient wavelength tuning-trimming schemes. Device compactness ensures a considerable reduction in the device footprint, power consumption, and parasitics. Furthermore, high fabrication yields obtained thanks to the state-of-the-art molecular wafer bonding of III-V alloys on silicon conjugate excellent device performances with cost-effective high-throughput production, indicating strong perspective industrial potential.
    Proc SPIE 03/2013;
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    ABSTRACT: It is well known that high-contrast metastructures can be exploited to perform a controllable coupling between matter and electromagnetic radiation. At optical frequencies this paves the way toward an arbitrarily adjustable spatio-temporal molding of light at the wavelength scale. In detail, high-index-contrast periodic structures such as photonic crystal membranes (PCMs) can be used for controlling the resonant coupling of radiated light to "heavy photons" states in strongly corrugated waveguides, thus putting photons through a slowed-down transport regime which results in an efficient quasi-3D light harnessing. More recently, one-dimensional Si/SiO2 photonic crystals have been adopted as compact, flexible, and power-efficient mirrors in vertical-cavity surfaceemitting lasers (VCSELs) emitting in the C-band which have been realized within a mass-scale fabrication paradigm by employing standard 200-mm microelectronics pilot lines. The extreme flexibility of such innovative photonic architecture enables to perform a fully-controllable transverse mode filtering, including polarization and far-field control, while the strong near-field mode overlap within mirrors can be exploited to implement unique optical functions such as on-chip optical routing and enhanced sensing capabilities. Furthermore, the device compactness ensures a considerable reduction in footprint, power consumption and parasitics, adding in required features for broadband modulation and high-speed data processing. High fabrication yields obtained via molecular wafer bonding of III-V alloys on silicon conjugate excellent device performances with cost-effective high-throughput production, addressing industrial needs for a fast research-tomarket transfer. In conclusion, photonic crystal VCSELs constitute thus a robust high-performance building block for the follow-through of semiconductor lasers, VCSEL and silicon photonics.
    Proc SPIE 03/2013;
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    ABSTRACT: Uniquely and arbitrarily shaped photonic crystal laser cavities were designed, fabricated and characterised. Room temperature lasing emitting at about 1550 nm was observed for all devices when photopumped by an 830 nm wavelength pulse laser with a pulse width of 100 ns. Continuous-wave lasing was even observed for select devices.
    Electronics Letters 01/2013; 49(25):1633-1635. · 1.04 Impact Factor
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    ABSTRACT: In this paper, we will present a new kind of structure that has the ability to trap nanometric particles and presents big capture cross section. This approach relies on the use of slow Bloch mode in a photonic crystal cavity. We will show how a new kind of design allows for an easy coupling of this kind of structure. FDTD modeling of the optical forces will be presented. We will show that the light intensity modulation related to the periodicity of the photonic crystal gives rise to strong gradient forces that are able to trap small nanoparticles in a large cavity. Experimental results validating this approach will be presented.
    Transparent Optical Networks (ICTON), 2013 15th International Conference on; 01/2013
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    ABSTRACT: CMOS-compatible III-V/Si vertical-cavity surface-emitting lasers (VCSELs) based on a double set of photonic crystal reflectors are demonstrated, showing single-mode continuous-wave operation at 1.55-μm with thresholds in the sub-mW range. The natural propensity of these VCSEL devices for achieving a wide range of functionality is discussed.
    Photonics Society Summer Topical Meeting Series, 2013 IEEE; 01/2013
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    ABSTRACT: We present the fabrication of graphene by chemical vapour deposition (CVD) on nickel foils. The growth process was optimized for formation of large area and high quality graphene monolayer films. The film quality was confirmed by Raman spectroscopy. Although the absorbance of a bare single graphene layer is limited to 2.3%, we show theoretically that it can be enhanced to 50% by integration with a resonant reflective membrane based on one-dimensional (1D) photonic crystal (PC) slab. The absorbance of a graphene monolayer combined with a PC membrane slab was increased up to 16%, experimentally.
    physica status solidi (b) 11/2012; · 1.49 Impact Factor
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    ABSTRACT: We demonstrate a method to reduce the mode volume of optical micro/nanocavities by positioning an opaque microtip in close proximity of the structures. This concept is used to blueshift the resonance of an active photonic crystal nanocavity by up to 16 nm. This tuning range is shown to be about 10 times larger than the redshift achieved with a bare dielectric microtip of the same size and shape. By imagining materials or multilayered devices with the ability to become transparent and opaque under external control, the blue and redshifts of the resonance would become possible with a single perturbing device.
    Applied Physics Letters 07/2012; 101(5). · 3.79 Impact Factor
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    ABSTRACT: In this paper, we present the integration of combined front and back 1D and 2D diffraction gratings with different periods, within thin film photovoltaic solar cells based on crystalline silicon layers. The grating structures have been designed considering both the need for incident light absorption enhancement and the technological feasibility. Long wavelength absorption is increased thanks to the long period (750 nm) back grating, while the incident light reflection is reduced by using a short period (250 nm) front grating. The simulated short circuit current in a solar cell combining a front and a back grating structures with a 1.2 µm thick c-Si layer, together with the back electrode and TCO layers, is increased up to 30.3 mA/cm2, compared to 18.4 mA/cm2 for a reference stack, as simulated using the AM1.5G solar spectrum intensity distribution from 300 nm to 1100 nm, and under normal incidence.
    Optics Express 07/2012; 20(S5):A560-A571. · 3.55 Impact Factor
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    ABSTRACT: In this paper, we present the integration of an absorbing photonic crystal within a monocrystalline silicon thin film photovoltaic stack fabricated without epitaxy. Finite difference time domain optical simulations are performed in order to design one- and two-dimensional photonic crystals to assist crystalline silicon solar cells. The simulations show that the 1D and 2D patterned solar cell stacks would have an increased integrated absorption in the crystalline silicon layer would increase of respectively 38% and 50%, when compared to a similar but unpatterned stack, in the whole wavelength range between 300 nm and 1100 nm. In order to fabricate such patterned stacks, we developed an effective set of processes based on laser holographic lithography, reactive ion etching and inductively coupled plasma etching. Optical measurements performed on the patterned stacks highlight the significant absorption increase achieved in the whole wavelength range of interest, as expected by simulation. Moreover, we show that with this design, the angle of incidence has almost no influence on the absorption for angles as high as around 60°.
    Optics Express 07/2012; 20 Suppl 4:A465-75. · 3.55 Impact Factor
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    ABSTRACT: In this paper, we propose a method for tailoring the absorption in a photonic crystal membrane. For that purpose, we first applied time domain coupled mode theory to such a subwavelength membrane and demonstrated that 100% resonant absorption can be reached even for a symmetric membrane, if degenerate modes are involved. Design rules were then derived from this model in order to tune the absorption. Subsequently, finite difference time domain simulations were used as a proof of concept and carried out on a low absorbing material (extinction coefficient = 10−2) with a high refractive index corresponding to the optical indices of amorphous silicon at around 720 nm. In doing so, 85% resonant absorption was obtained, which is significantly higher than the commonly reported 50% maximum value. Those results were finally analyzed and confronted to theory so as to extend our method to other materials, configurations and applications.
    Journal of Applied Physics 06/2012; 111(12-111):123114. · 2.21 Impact Factor

Publication Stats

975 Citations
293.45 Total Impact Points


  • 1996–2013
    • Ecole Centrale de Lyon
      • Institut des Nanotechnologies de Lyon
      Rhône-Alpes, France
  • 2002–2012
    • French National Centre for Scientific Research
      • Laboratory for Photonics and Nanostructures - LPN
      Lutetia Parisorum, Île-de-France, France
  • 2011
    • CERN
      Genève, Geneva, Switzerland
  • 2010
    • Cea Leti
      Grenoble, Rhône-Alpes, France
  • 2007–2009
    • Ghent University
      • Department of Information Technology
      Gent, VLG, Belgium
    • University of Valencia
      Valenza, Valencia, Spain
  • 2008
    • Spanish National Research Council
      • Instituto de Microelectrónica de Madrid
      Madrid, Madrid, Spain
  • 2006
    • Australian National University
      • Department of Electronic Materials Engineering (EME)
      Canberra, Australian Capital Territory, Australia
  • 2005
    • Laboratoire de Photonique et de Nanostructures
      Île-de-France, France