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Laboratoire d’analyse et d’architecture des systèmes

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18172
01/07/2018

Anisotropy in the wet thermal oxidation of AlGaAs: influence of process parameters

G.LAFLEUR, G.ALMUNEAU, A.ARNOULT, H.CAMON, S.CALVEZ

PHOTO, TEAM

Revue Scientifique : Optical Materials Express, Vol.8, N°7, pp.394-396, Juillet 2018 , N° 18172

Lien : https://hal.laas.fr/hal-01810561

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The crystallographic anisotropy of the lateral selective thermal oxidation of AlGaAs alloys is experimentally studied. The anisotropic behavior of this oxidation process, used primarily for building a lateral confinement in vertical surface emitting lasers (VCSEL), is quantified by varying different process parameters and the geometrical shapes of laterally oxidized mesa structures. This experimental study aims to have a better control of the oxide aperture shape used in oxide-confined photonics devices.

143919
18150
01/07/2018

Modelling anisotropic lateral oxidation from circular mesas

S.CALVEZ, G.LAFLEUR, A.ARNOULT, A.MONMAYRANT, H.CAMON, G.ALMUNEAU

PHOTO, TEAM

Revue Scientifique : Optical Materials Express, Vol.8, N°7, pp.1762-1773, Juillet 2018 , N° 18150

Lien : https://hal.archives-ouvertes.fr/hal-01809678

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In this paper, an iterative method to model the anisotropic lateral oxidation of circular structures is proposed and validated by confrontation to experimental data. The described model enables the efficient calculation of the temporal bi-dimensional evolution of the oxidation front shape, starting from a circular mesa, and progressing inward as a result of an anisotropic process combining an isotropic diffusion with an anisotropic reaction. The result of the developed model shows that the oxide aperture smoothly deforms from a circle to become more diamond-like, mimicking the experimental situation encountered when fabricating vertical-cavity surface-emitting lasers (VCSELs) on (100) wafers or, more generally, when oxidizing circular mesas of aluminum-containing III-V semiconductor on similarly oriented substrates.

143824
18102
01/06/2018

Coupled-mode analysis of vertically-coupled AlGaAs/AlOx microdisk resonators

C.ARLOTTI, G.LAFLEUR, A.LARRUE, P.F.CALMON, A.ARNOULT, G.ALMUNEAU, O.GAUTHIER-LAFAYE, S.CALVEZ

PHOTO, TEAM

Revue Scientifique : IEEE Journal of Quantum Electronics, Vol.54, N°3, Juin 2018 , N° 18102

Lien : https://hal.laas.fr/hal-01741465

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This article reports the experimental and theoretical assessments of the optical characteristics of recently-introduced vertically-coupled microdisk resonators made by selective oxidation of AlGaAs multilayer structures. Experimental measurements show that the Q-factors are in the 10 3 to 10 4 range for diameters ranging from 75 to 300 µm. To establish the origins of this limited performance a coupled-mode-theory-based model of the single-access-waveguide-coupled resonator system was developed. It includes features which are specific to oxide-based vertically-coupled resonators, namely losses towards the slab waveguide lying under the resonator and a coupling region with an asymmetric and multilayer structure. Setting this simulation tool required the proposal and validation of a general criterion to select an appropriate set of decomposition permittivity profiles to be able to accurately model the characteristics of these more complex couplers using the coupled-mode-theory approach. This theoretical development is generic and can be now deployed to simulate any device which includes multi-waveguide couplers with arbitrary piece-wise-constant profile of the dielectric permittivity. Exploiting this particular development and experimental measurements of the disk sidewall roughness and of the coupling lengths, the calculated and experimental Q-factors are found to be in good agreement and allow establishing that the current performance is limited by the scattering losses and the slab-leakage losses for small-and large-diameter devices respectively.

143354
18208
25/05/2018

Active control of light extraction in the near-IR range with sub-wavelength periodic structures

A.HELIOT, S.PELLOQUIN, O.GAUTHIER-LAFAYE, A.MONMAYRANT, H.CAMON, T.GACOIN, K.LAHLIL, L.MARTINELLI, C.BIVER, S.ARCHAMBEAU

PHOTO, LPMC, Essilor Int, Tlse

Manifestation avec acte : Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS ( DTIP ) 2018 du 22 mai au 25 mai 2018, Rome (Italie), Mai 2018 , N° 18208

Lien : https://hal.archives-ouvertes.fr/hal-01842005

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Due to their narrow reflection peak as well as their compact structure, Guided Mode Resonance Filters (GMRFs) are attractive for many applications. We demonstrate the possibility to modulate the properties of a GMRF by associating with liquid crystals (LCs). By impregnating the diffraction grating with LCs, it is possible to switch between an active and an inactive state depending on the polarization of the light or the applied voltage. In this paper we fabricated and characterized the first diffraction order of LC-impregnated gratings with different periods (0,8 to 5,0μm) and depths (130 to 840nm) to test the ability of liquid crystals to adjust the diffraction properties. Finally, 99.8% of diffraction turn off with a 90° rotation polarization at zero voltage and 90 to 99% by applying a voltage of 30 V according to the grating dimensions. The effect of the grating dimension on the diffraction modulation capacity will be discussed.

144197
18127
22/04/2018

Design of an Electro-absorption modulator for integration onto a VCSEL

L.MARIGO-LOMBART, S.CALVEZ, A.ARNOULT, A.RUMEAU, C.VIALLON, H.THIENPONT, G.ALMUNEAU, K.PANAJOTOV

PHOTO, TEAM, I2C, MOST, Bruxelles

Manifestation avec acte : SPIE Photonics Europe. Semiconductor Lasers and Laser Dynamics VII ( SPIE photonics ) 2018 du 22 avril au 26 avril 2018, Strasbourg (France), Avril 2018, 2p. , N° 18127

Lien : https://hal.laas.fr/hal-01780281

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In this work, we have realized a complete optimization cycle from structure design, fabrication to devices characterization, and finally analysis b ased on our model of Asymmetric - Fabry - Perot vertica l electro - absorption modulator. In order to achieve enhanced dynamic absorption effect with a minimized number of MQW, we used a perturbative quantum - confined Stark - effect based on a simple absorption mode l and transfer matrix calculations and optimize the modulation figures of merit as a function of different design parameters under varying applied electrical fields. The epitaxial growth by MBE of different EAM and EAM - VCSEL structures has been done, supp orted by intermediate optical measurements enabling to identify the EAM cavity and VCSEL cavity respective positions. Finally, first static characterizations are done and demonstrate the expected modulation properties of the device. A very good agreement of theoretical predictions for both the effect of the applied field and the temperature on the excitonic peak position and the Fabry - Perot shift experimentally measured on different fabricated EAM structures has been achieved. Thanks to th is, we are now able to design an optim al VCSEL structure with integrated electro - absorption modulator . To aim for very high frequency efficient electrical injection we focused also on the BCB characterization up to 110 Ghz and the injection scheme de sign specific to this triple electrode device. These measurements are of high interest for the optimum design of the access while considering the parasitic effects. We then compare coplanar and micro strip lines access, with a taper or not, to decrease the pad capacitance and so increase the cut - off frequency.

143573
17479
02/03/2018

Soft mold NanoImprint Lithography: A versatile tool for sub-wavelength grating applications

S.PELLOQUIN, S.AUGÉ, K.SHARSHAVINA, J.B.DOUCET, A.HELIOT, H.CAMON, O.GAUTHIER-LAFAYE

PHOTO, TEAM

Revue Scientifique : Microsystem Technologies, 5p., Mars 2018 , N° 17479

Lien : https://hal.laas.fr/hal-01706924

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Due to its independency to the substrate used, Soft mold NanoImprint Lithography (S-NIL) is a technique of great interest in particular for the fabrication of optical devices. We demonstrate a mature pathway for the realization of optical filters from the conception to the optical characterization. Those filters can be realized on large surfaces (up to 6" diameter wafers) with high conformity on various substrates. Quality of the transfer will be discussed throughout the process and optical performances compared to those obtained with classical techniques. In this paper we fabricated tunable spectral filters with a grating periodicity down to 260 nm and imprint surfaces up to 6". Physical conformity of the gratings will be discussed in terms of long-range stitching obtained on 6" Si hard mold, dimensional shrinkage during thermal NanoImprint on Zeonor® soft mold and conformity towards patterned hard mold throughout the process.

142589
18110
01/03/2018

Effect of low and staggered gap quantum wells inserted in GaAs tunnel junctions

K.LOUARN, Y.CLAVEAU, L.MARIGO-LOMBART, C.FONTAINE, A.ARNOULT, F.PIQUEMAL, A.BOUNOUH, N.CAVASSILAS, G.ALMUNEAU

PHOTO, IM2NP, TEAM, LNE, CEA LIST

Revue Scientifique : Journal of physics. D, Applied physics, Vol.51, N°14, 145107p., Mars 2018 , N° 18110

Lien : https://hal.archives-ouvertes.fr/hal-01761772

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In this article, we investigate the impact of the insertion of either a type I InGaAs or a type II InGaAs/GaAsSb quantum well on the performances of MBE-grown GaAs tunnel junctions (TJs). The devices are designed and simulated using a quantum transport model based on the non-equilibrium Green's function formalism and a 6-band k.p Hamiltonian. We experimentally observe significant improvements of the peak tunneling current density on both heterostructures with a 460-fold increase for a moderately doped GaAs TJ when the InGaAs QW is inserted at the junction interface, and a 3-fold improvement on a highly doped GaAs TJ integrating a type II InGaAs/GaAsSb QW. Thus, the simple insertion of staggered band lineup heterostructures enables us to reach a tunneling current well above the kA cm−2 range, equivalent to the best achieved results for Si-doped GaAs TJs, implying very interesting potential for TJ-based components, such as multi-junction solar cells, vertical cavity surface emitting lasers and tunnel-field effect transistors.

143394
18100
01/03/2018

Vertical electro-absorption modulator design and its integration in a VCSEL

L.MARIGO-LOMBART, S.CALVEZ, A.ARNOULT, H.THIENPONT, G.ALMUNEAU, K.PANAJOTOV

PHOTO, TEAM, Bruxelles

Revue Scientifique : Journal of physics. D, Applied physics, Vol.51, N°14, 145101p., Mars 2018 , N° 18100

Lien : https://hal.laas.fr/hal-01780259

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Electro-absorption modulators, either embedded in CMOS technology or integrated with a semiconductor laser, are of high interest for many applications such as optical communications, signal processing and 3D imaging. Recently, the integration of a surface-normal electro-absorption modulator into a vertical-cavity surface-emitting laser has been considered. In this paper we implement a simple quantum well electro-absorption model and design and optimize an asymmetric Fabry–Pérot semiconductor modulator while considering all physical properties within figures of merit. We also extend this model to account for the impact of temperature on the different parameters involved in the calculation of the absorption, such as refractive indices and exciton transition broadening. Two types of vertical modulator structures have been fabricated and experimentally characterized by reflectivity and photocurrent measurements demonstrating a very good agreement with our model. Finally, preliminary results of an electro-absorption modulator vertically integrated with a vertical-cavity surface-emitting laser device are presented, showing good modulation performances required for high speed communications.

143337
18099
01/02/2018

Scanning microwave microscopy applied to semiconducting GaAs structures

A.BUCHTER, J.HOFFMANN, A.DELVALLEE, E.BRINCIOTTI, D.HAPIUK, C.LICITRA, K.LOUARN, A.ARNOULT, G.ALMUNEAU, F.PIQUEMAL, M.Zeier, F.KIENBERGER

METAS, LNE, Keysight, CEA-LETI, PHOTO, TEAM

Revue Scientifique : Review of Scientific Instruments, Vol.89, N°2, 023704p., Février 2018 , N° 18099

Lien : https://hal.laas.fr/hal-01780256

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A calibration algorithm based on one-port vector network analyzer (VNA) calibration for scanning microwave microscopes (SMMs) is presented and used to extract quantitative carrier densities from a semiconducting n-doped GaAs multilayer sample. This robust and versatile algorithm is instrument and frequency independent, as we demonstrate by analyzing experimental data from two different, cantilever- and tuning fork-based, microscope setups operating in a wide frequency range up to 27.5 GHz. To benchmark the SMM results, comparison with secondary ion mass spectrometry is undertaken. Furthermore, we show SMM data on a GaAs p-n junction distinguishing p- and n-doped layers.

143335
18010
23/01/2018

Etude et réalisation de jonctions tunnel à base d'hétérostructures à semiconducteurs III-V pour les cellules solaires multi-jonction à très haut rendement

K.LOUARN

PHOTO

Doctorat : Université de Toulouse III - Paul Sabatier, 23 Janvier 2018, 197p., Président: C.ALONSO, Rapporteurs: J.C.HARMAND, J.CONNOLLY, Examinateurs: Y.ROUILLARD, Directeurs de thèse: G.ALMUNEAU, A.BOUNOUH , N° 18010

Lien : https://hal.laas.fr/tel-01705164

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Multi-Jonction Solar Cells (MJSCs) are leading the way of high efficiency photovoltaic devices, with conversion efficiency up to 46%. Their subcells are designed to absorb in a specific and complementary range of the solar spectrum, and are connected in series with tunnel junctions. The tandem architecture InGaP/GaAs - with bandgaps of 1.87 eV and 1.42 eV respectively - is mature and its efficiency could be enhanced by incorporating subcell(s) with bandgaps of 1 eV and/or 0.7 eV. The Molecular Beam Epitaxy (MBE) growth of such low bandgap materials has thus to be developed, as well as low-resistive tunnel junctions with good structural and optical properties. Based on the MBE growth and the simulation of GaAs tunnel junctions, we have identified interband tunneling as the predominant transport mechanism in such devices rather than trap-assisted-tunneling. The interband tunneling mechanism could be enhanced with the type II GaAsSb/InGaAs heterostructure. Using this material system, we have then demonstrated tunnel junctions with very low electrical resistivity with a limited degradation of the optical and structural properties inherently induced by the use of low band-gap and lattice-mismatched GaAsSb and InGaAs materials. Moreover, we fabricated an innovative AlInGaAs/AlGaAsSb tunnel junction as a graded buffer architecture that could be used for the incorporation of a 1 eV metamorphic subcell. We then developed and characterized InGaAsN(Bi) materials with band-gaps of ~1eV, taking advantage of in-situ wafer curvature measurements during the MBE growth to control the lattice-mismatch. Preliminary solar cells based on GaAs, 1 eV dilute nitride and metamorphic InGaAs have been fabricated and characterized validating the developed tunnel junction architectures. This work has enabled to demonstrate the potential of the type II GaAsSb/InGaAs heterostructure to meet the challenges posed by the conception and the fabrication of GaAsbased MJSCs, both for the tunnel junction and the 1 eV subcell.

Résumé

L’architecture des cellules solaires multi-jonction permet d’obtenir des records de rendement de conversion photovoltaïque, pouvant aller jusqu’à 46%. Leurs sous-cellules sont chacune conçues pour absorber une partie bien définie et complémentaire du spectre solaire, et sont connectées en série par des jonctions tunnel. La fabrication de cellules solaires tandem InGaP/GaAs d’énergies de bande interdite (« band gap ») 1,87 eV/1,42 eV accordées en maille sur substrat GaAs est bien maîtrisée, et de très hauts rendements peuvent être obtenus en ajoutant une ou deux sous-cellules de plus petit « gap » (1 eV et 0,7eV). Pour cela, les matériaux « petits gaps » fabriqués par Epitaxie par Jets Moléculaires (EJM) doivent être développés ainsi que des jonctions tunnel présentant une faible résistivité électrique, une haute transparence optique et de bonnes propriétés structurales. La croissance EJM et la modélisation de jonctions tunnel GaAs nous a permis d’identifier le mécanisme d’effet tunnel interbande plutôt que le mécanisme d’effet tunnel assisté par les défauts comme mécanisme dominant du transport dans ces structures. Nous avons exploité l’hétérostructure de type II fondée sur le système GaAsSb/InGaAs pour favoriser ce mécanisme d’effet tunnel interbande, et donc obtenir des jonctions tunnel de très faible résistivité tout en limitant la dégradation des propriétés optiques et structurales des composants inhérente à l’utilisation de matériaux « petits gaps » et désaccordés en maille GaAsSb et InGaAs. De plus, nous avons conçu une structure innovante d’hétérojonction tunnel de type II AlGaInAs/AlGaAsSb sous la forme de tampon graduel pour l’incorporation d’une sous-cellule métamorphique à 1 eV. Plusieurs candidats pour le matériau absorbeur à 1 eV à base de nitrure dilué InGaAsN(Bi) ont alors été développés et caractérisés, le contrôle de l’accord de maille étant assuré par un suivi en temps réel de la courbure de l’échantillon pendant la croissance EJM. Des premières cellules solaires III-V à base de GaAs, de nitrure dilué à 1 eV et de GaInAs métamorphique ont été fabriquées afin de valider les architectures développées de jonctions tunnel. Ce travail a permis de démontrer le potentiel de l’hétérostructure de type II GaAsSb/InGaAs pour répondre aux principaux défis de conception et de fabrication des cellules solaires multi-jonction sur substrat GaAs, que ce soit au niveau de la jonction tunnel ou au niveau de l’incorporation des sous-cellules de gap 1 eV.

Mots-Clés / Keywords
Photovoltaïque; Epitaxie; Cellules solaires multi-jonction; Semiconducteurs III-V; Jonction tunnel; Photovoltaic; Epitaxy; Multi-junction solar cells; III-V semiconductors; Tunnel junction;

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