Laboratoire d’analyse et d’architecture des systèmes
C.ARLOTTI, O.GAUTHIER-LAFAYE, A.MONMAYRANT, S.CALVEZ
Revue Scientifique : Journal of the Optical Society of America. B, Optical physics, Vol.34, N°11, pp.2343-2351, Novembre 2017 , N° 17386
In this paper, we investigate the spectral response of whispering-gallery-mode (WGM) resonators coupled to their access waveguide with a view to design their constitutive waveguides to promote critical-coupling over a wide spectral range and thereby facilitate their use for high-sensitivity sensing or nonlinear frequency conversion applications. The carried-out theoretical analysis is based on the universal response functions of singlemode and unidirectional devices. A coupled-mode treatment of the coupling region enables to derive two sets of favorable designs. The identified resonator/access waveguide systems exploit waveguides with mismatched propagation constants forming a coupling section exhibiting either an achromatic beat-length or an achromatic power-transfer coefficient. This generic model is followed by a numerical case study of vertically-coupled Si3N4 racetrack resonators. The conventional (quasi-)phase-matched configuration, treated as a reference case, is shown to display a critical-coupling bandwidth of 23 nm at a wavelength of 1550nm, whereas the proposed new designs demonstrate critical bandwidths larger than 330nm, i.e. exhibit bandwidths enhanced by more than one order of magnitude.
L.MARIGO-LOMBART, S.CALVEZ, A.ARNOULT, A.RUMEAU, C.VIALLON, H.THIENPONT, K.PANAJOTOV, G.ALMUNEAU
PHOTO, TEAM, I2C, MOST, Bruxelles
Rapport LAAS N°17401, Octobre 2017
VCSELs became dominant laser sources in many short optical link applications such as datacenter, active cables, etc. Actual standards and commercialized VCSEL are providing 25 Gb/s data rates, but new solutions are expected to settle the next device generation enabling 100 Gb/s. Directly modulated VCSEL have been extensively studied and improved to reach bandwidths in the range of 26-32 GHz [Chalmers, TU Berlin], however at the price of increased applied current and thus reduced device lifetime. Furthermore, the relaxation oscillation limit still subsists with this solution. Thus, splitting the emission and the modulation functions as done with DFB lasers is a very promising alternative [TI-Tech, TU Berlin]. Here, we study the vertical integration of an Electro-Absorption Modulator (EAM) within a VCSEL, where the output light of the VCSEL is modulated through the EAM section. In our original design, we finely optimized the EAM design to maximize the modulation depth by implementing perturbative Quantum Confined Stark Effect (QCSE) calculations, while designing the vertical integration of the EAM without penalty on the VCSEL static performances. We will present the different fabricated vertical structures, as well as the experimental electrical and optical static measurements for those configurations demonstrating a very good agreement with the reflectivity and absorption simulations obtained for both the VCSEL and the EAM-VCSEL structures. Finally, to reach very high frequency modulation we studied the BCB electrical properties up to 110 GHz and investigated coplanar and microstrip lines access to decrease both the parasitic capacitance and the influence of the substrate. 100 words: In this presentation, we describe the operation of Multiple-Quantum-Wells Asymmetric Fabry-Perot modulator, vertically integrated into a VCSEL structure for high-speed modulation. First we optimize the Electro-Absorptive Modulator (EAM) and the EAM-VCSEL structures by utilizing a perturbative quantum-confined Stark-effect and transfer matrix calculations. Then we present experimental reflectivity, LIV curves and photocurrent measurements and demonstrate very good agreement with our modelling results. High frequency measurements of BCB electrical response up to 110 GHz are carried out to estimate the parasitic effects due to the pad configuration and the impact of the substrate.
F.DYBALA, J.KOPACZEK, E.M.PAVELESCU, C.ROMANITAN, O.LIGOR, A.ARNOULT, C.FONTAINE, R.KUDRAWIEC
Wroclaw University, IMT, TEAM, PHOTO
Rapport LAAS N°17396, Octobre 2017, 24p.
L.MARIGO-LOMBART, S.CALVEZ, A.ARNOULT, H.THIENPONT, K.PANAJOTOV, G.ALMUNEAU
PHOTO, TEAM, Bruxelles
Revue Scientifique : Semiconductor Science and Technology, 5p., Octobre 2017, DOI 10.1088/1361-6641/aa90ae , N° 17379
We propose a simplified and easier fabrication process flow for the manufacturing of AlOx-confined VCSELs based on combining the oxidation step with a self-aligned process, allowing the mesa etching and two successive lift-off steps based on a single lithography step. The electro-optical confinement achieved by standard lateral oxidation enables a low threshold and a single mode behaviour for the VCSEL. This simplified process can largely improve VCSEL manufacturing by reducing the processing time and costs compared to the standard VCSEL process. Introduction: Vertical-cavity surface-emitting lasers (VCSEL) have become the preferred light sources in many photonic systems, enabling short-link interconnections  but also in other emerging mass-market applications like sensing and detection . The large production volume of VCSELs would benefit from a simplification of the manufacturing process flow that may largely increase the cost-effectiveness. Indeed, compared to the LED and LDs, the VCSEL fabrication process flow requires a large number of elementary steps defined by successive inter-aligned photolithography levels. A precision in the micron range is required to ensure the lateral alignment between the optical waveguide and the electrical injection. For these reasons, one of the most important concerns for the VCSEL manufacturers is to improve the production throughput by lowering the fabrication time and cost per wafer. The development of a self-aligned process is of great interest as already demonstrated for the fabrication of high performance HBT transistors or ridge lasers [3,4]. To that extent, Al-Omari  used a top metallic contact deposited over a photoresist layer as a hard mask to dry-etch the VCSEL mesa. Chua  developed a pseudo-planar approach by opening via holes down to the AlAs layer to carry out the lateral oxidation. This process has subsequently been improved by Strzelecka  to increase the device density. Recently, we have shown that air-post VCSELs could be created using an innovative self-aligned process, which combined several masking and lift-off steps defined by a single lithographic step . In this paper, we extend this work and propose a new process flow to fabricate, in a very simple and straightforward way, the widely-used oxide-confined VCSELs. The demonstrated process drastically simplifies the oxide-confined VCSEL fabrication by reducing the total number of lithographic alignment steps from four or more to only one alignment, with the additional advantage of relieving the required tolerances. This process flow, most suitable for 3D imaging and sensing applications, can also be easily implemented for the fabrication of other optoelectronic devices such as modulators, ridge waveguide lasers, detectors, solar cells or any process combining dry etch, passivation and metallization.
K.LOUARN, Y.CLAVEAU, A.ARNOULT, C.FONTAINE, J.COLIN, C.CORNILLE, I.MASSIOT, L.MARIGO-LOMBART, F.PIQUEMAL, A.BOUNOUH, N.CAVASSILAS, G.ALMUNEAU
PHOTO, IM2NP, TEAM, LNE, CEA LIST
Manifestation avec acte : Réunion plénière du GDR PULSE ( ) 2017 du 02 octobre au 05 octobre 2017, Paris (France), Octobre 2017, 3p. , N° 17382
Les Jonctions Tunnel (JT) sont des composants très importants pour les cellules solaires multi-jonction, puisqu'elles assurent la connexion électrique en série entre les différentes sous-cellules. Récemment, il a été fabriqué par EPVOM des JTs AlGaAs:C/GaAs:Te et AlGaAs:C/GaInP:Te atteignant des densités de courant pic J pic records de 10 kA/cm² sur substrat GaAs , en remplaçant le dopant N usuel Si par du Te et permettant ainsi d'obtenir les forts niveaux de dopages nécessaires pour augmenter la probabilité d'effet tunnel dans le composant. Nous avons travaillé sur une autre approche pour obtenir des JT de "hautes" performances, et ne nécessitant pas des dopages aussi forts : il s'agit de profiter des offsets de bandes de l'hétérojonction AlGaAsSb/AlGaInAs de type II pour augmenter la probabilité d'effet tunnel.
K.LOUARN, Y.CLAVEAU, A.ARNOULT, C.FONTAINE, J.COLIN, C.CORNILLE, F.PIQUEMAL, A.BOUNOUH, N.CAVASSILAS, G.ALMUNEAU
PHOTO, IM2NP, TEAM, LNE, CEA LIST
Manifestation avec acte : European Photovoltaic Solar Energy Conference and Exhibition ( EU PVSEC ) 2017 du 25 septembre au 29 septembre 2017, Amsterdam (Pays-Bas), Septembre 2017 , N° 17391
Aim and approach-Tunnel Junctions (TJs) are key devices for monolithic Multi-Junction Solar Cells (MJSCs), in which they ensure the series interconnection between the subcells. For GaAs based MJSCs, very low resistive (with peak tunneling current density J peak up to 10 kA/cm²) AlGaAs:C/GaInP:Te or AlGaAs:C/GaAs:Te have been recently developed by MOVPE using Te instead of Si as N-dopant making it possible to get the heavily doping levels needed for tunneling optimization . In this work, we investigate an alternative to this approach. The tunneling probability is increased through the engineering of band-offset thanks to the use of a type II (Al)GaAsSb/(Al)InGaAs staggered heterojunction. Such TJs are suitable for both lattice-matched and metamorphic MJSCs. Scientific innovation and relevance – MBE was used to grow pseudomorphic and metamorphic (Al)GaAsSb/(Al)InGaAs TJs (5% to 10 % In and Sb contents) on GaAs substrate, where Aluminium enables to limit light absorption in the TJ. We have experimentally and theoretically investigated the role of the layer thicknesses on the tunneling mechanisms to propose TJ heterostructure designs suitable for lattice-matched MJSCs and metamorphic MJSCs. Preliminary results and conclusions-For relatively thin [10 to 30 nm] type II TJs, the incorporation of Sb/In in the GaAs TJ is actually degrading the electrical performances, with J peak decreasing from 180 A/cm² for simple GaAs TJ to 70 A/cm² for GaAs 0.95 Sb 0.05 /In 0.05 Ga 0.95 As TJs. On the other hand, thicker 100 nm (Al)GaASb/(Al)InGaAs TJs present the expected tunneling current density increase with J peak close to 1000 A/cm². It worths to note that such thick TJs lead to strain/relaxation issues that could be detrimental for lattice-matched MJSCs but beneficial for metamorphic MJSCs. The origin of this difference in behavior is under investigation both using a semi-classical model  and a Non Equilibrium Green's Function based quantum model . First simulations suggest that it originates from a balance between quantum confinement and type II-related tunneling probability enhancement. Based on these results, we are developing GaAs/InGaAs/GaAsSb/GaAs TJs suitable for lattice-matched MJSCs with preliminary measurements showing a thousand-fold increase of the peak tunneling current. Complementary, we are studying the relaxation mechanisms of (Al)Ga(In)As(Sb) alloys using in-situ MBE stress measurements in order to optimize the growth of metamorphic (Al)GaAsSb/(Al)InGaAs TJs.
K.LOUARN, Y.CLAVEAU, D.HAPIUK, C.FONTAINE, A.ARNOULT, T.TALIERCIO, C.LICITRA, F.PIQUEMAL, A.BOUNOUH, N.CAVASSILAS, G.ALMUNEAU
PHOTO, IM2NP, CEA-LETI, TEAM, IES, LNE, CEA LIST
Revue Scientifique : Journal of physics. D, Applied physics, Vol.50, N°38, 385109p., Septembre 2017 , N° 17365
The aim of this study is to investigate the impact of multiband corrections on the current density in GaAs tunnel junctions (TJs) calculated with a refined yet simple semi-classical interband tunneling model (SCITM). The non-parabolicity of the considered bands and the spin–orbit effects are considered by using a recently revisited SCITM available in the literature. The model is confronted to experimental results from a series of molecular beam epitaxy grown GaAs TJs and to numerical results obtained with a full quantum model based on the non-equilibrium Green's function formalism and a 6-band k.p Hamiltonian. We emphasize the importance of considering the non-parabolicity of the conduction band by two different measurements of the energy-dependent electron effective mass in N-doped GaAs. We also propose an innovative method to compute the non-uniform electric field in the TJ for the SCITM simulations, which is of prime importance for a successful operation of the model. We demonstrate that, when considering the multiband corrections and this new computation of the non-uniform electric field, the SCITM succeeds in predicting the electrical characteristics of GaAs TJs, and are also in agreement with the quantum model. Besides the fundamental study of the tunneling phenomenon in TJs, the main benefit of this SCITM is that it can be easily embedded into drift-diffusion software, which are the most widely-used simulation tools for electronic and opto-electronic devices such as multi-junction solar cells, tunnel field-effect transistors, or vertical-cavity surface-emitting lasers.
K.SHARSHAVINA, P.ARGUEL, P.F.CALMON, F.CARCENAC, E.DARAN, X.DOLLAT, J.B.DOUCET, P.DUBREUIL, O.GAUTHIER-LAFAYE, A.LECESTRE, A.LESTRAS, L.MAZENQ, A.MONMAYRANT, S.PELLOQUIN
PHOTO, TEAM, I2C
Rapport de Contrat : Convention CNES n° 140301/00, Septembre 2017, 66p. , N° 17328
I.PASQUET, H.LE TRONG, V.BACO-CARLES, L.PRESMANES, C.BONNINGUE, V.BAYLAC, P.TAILHADES, V.CONEDERA, P.F.CALMON, D.DRAGOMIRESCU, H.CAMON
CIRIMAT, TEAM, MINC, PHOTO
Revue Scientifique : Journal of the European Ceramic Society, 17p., Septembre 2017, https://doi.org/10.1016/j.jeurceramsoc.2017.03.030 , N° 17162
Films of copper and cobalt-iron oxalates were prepared from suspensions of powders in ethane-1,2-diol deposited on glass or polycarbonate substrates. Two-dimensional structures of oxides, resolved on the scale of less than ten micrometers, were formed by laser insolation of these films, using a photolithography machine. The nature of the constitutive phases of the oxides formed tends to show that the laser heating makes it possible to reach locally, temperatures higher than 1000 °C. The oxides formed are thus sintered. The residual oxalate can be removed by washing or dissolving, leaving the oxide structure on its substrate. In spite of a perfectible sintering, the formed structures could interest different technological applications (electronic or magnetic devices, gas sensors, photovoltaic systems…) requiring the shaping of simple or mixed oxides on a scale close to the micrometer. The process of selective laser decomposition of oxalates, could subsequently be suitable for additive manufacturing of 3D parts.
I.ARDI, H.CARFANTAN, S.LACROIX, A.MONMAYRANT
PHOTO, IRAP, RIS
Manifestation avec acte : Colloque GRETSI sur le traitement du signal et des images ( GRETSI ) 2017 du 05 septembre au 08 septembre 2017, Juan les pins (France), Septembre 2017, 4p. , N° 17225
Nous nous intéressons à la reconstruction d'images hyperspectrales (HS) à partir d'un nouveau dispositif d'imagerie pilotable. La reconstruction de l'image à partir d'un faible nombre d'acquisitions pour des configurations différentes de l'imageur permet d'éviter l'acquisition de toute l'image HS par balayage. Notre objectif à terme est de rendre ce dispositif adaptatif en fonction de l'objet observé, ce qui nécessite de disposer de méthodes de reconstruction à faible coût calculatoire. Nous nous focalisons ici sur la reconstruction à l'aide de méthodes de pénalisation quadratique, permettant une résolution directe à faible coût, grâce au caractère très creux des matrices. Abstract – We consisder the problem of hyperspectral image reconstruction with a new controlable imaging system. The reconstruction with a small number of images acquired with different configurations of the imager avoids a complete scanning of the hyperspectral cube. Our objective is to exploit this imager along an adaptive scheme, which requires the ability to reconstruct images in near real-time. We focus here on a quadratic penalty reconstruction approach, which provides a fast direct resolution thanks to the high sparsity of the involved matrices.