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This work is devoted lo the localization of InAs quantum dots (QDs) grown by solid-source molecular beam epitaxy on nanostructured InP(001) surfaces, which will find application in quantum or classical devices operating at the wavelength of 1.55 /spl mu/m. The dots are grown on the mesas or in the holes, which are designed to be the sites of privileged nucleation of the quantum dots.

1D and 2D compact photonic crystal reflectors on suspended InP membranes are theoretically and experimentally studied under normal incidence. They are based on the coupling of free space waves with slow Bloch modes of the crystal. We first present monomodal 1D photonic crystal reflectors. Then, we focus on multimodal 1D reflectors, which involve two slow Bloch modes of the crystal, and thus present broadband high-efficiency characteristics. 2D broadband reflectors were also investigated. They allow for an accurate control on the polarization dependence of the reflection. A compact (50 μm x 50 μm) demonstrator was realized and characterized, behaving either as a broadband reflector or as a broadband transmitter, depending on the polarization of the incident wave (experimental stop-band superior to 200nm, theoretical stop-band of 350nm). These photonic crystal slabs can be used in new photonic devices as reflectors, where they can replace multilayer Bragg mirrors. The authors report a compact and highly selective tunable filter using a Fabry-Perot resonator combining a bottom micromachined 3-pair-InP/air-gap Bragg reflector with a top photonic crystal slab mirror. It is based on the coupling between radiated vertical cavity modes and waveguided modes of the photonic crystal. The full-width at half maximum (FWHM) of the resonance, as measured by microreflectivity experiments, is close to 1.5nm (around 1.55 μm). The presence of the photonic crystal slab mirror results in a very compact resonator, with a limited number of layers. The demonstrator was tuned over a 20nm range for a 4V tuning voltage, the FWHM being kept below 2.5nm.

This work is devoted to the localization of InAs quantum dots grown by SSMBE on nanostructured InP(001) surfaces: mesas or holes are the sites of privileged nucleation of the quantum dots (QDs). Both nanostructuration methods are compared. The principle of fabrication of a photonic crystal cavity based source with localized QDs is described.

The integration of a photonic layer on a CMOS circuit can be done either by wafer bonding of an SOI photonic circuit or by low temperature fabrication of a photonic layer at the metallization levels

One dimensional and two dimensional photonic crystal slabs have numerous applications in integrated optics. Unfortunately, due to their finite height, their in plane guided modes can suffer out-coupling losses. Although considered as detrimental in the context of the development of photonic integrated circuits, it turns that the coupling of wave-guided modes to radiative modes can be usefully exploited for the manipulation of photons in free space. It is shown in this paper that interaction of radiative and guided modes through a photonic crystal, especially under conditions where the later correspond to extreme of the dispersion characteristics of the photonic crystal, results in resonance phenomena which can be used practically for the development of new classes of devices, e.g. combining photonic crystal and MOEMS (micro opto electro mechanical systems) structures: PCMOEMS.

International audience; Micro-photoluminescence spectroscopy measurements have been performed on single self-organized InAs/InP quantum dashes, either on sub-micron mesas made on the sample surface or through sub-micron apertures realized in a gold mask deposited on the surface. The emission wavelength of the quantum dashes is centred around 1.5 µm at room temperature. The micro-photoluminescence measurements on sub-micron mesas, at low temperature and with low excitation power density, show PL spectra consisting of a few single sharp exciton lines with a rather large full width at half maximum (FWHM) in the 0.8–1.8 meV range, whereas peak broadening is found to be much smaller for the spectra recorded through the sub-micron apertures with an FWHM below 300 µeV. When the excitation power density is increased, new lines arise which are interpreted as emission coming from excited states of single InAs/InP quantum dashes and from bi-exciton recombination.

International audience; Micro-photoluminescence spectroscopy (μ-PL) as a function of excitation power density and temperature, is used to study single self-organized InAs/InP quantum sticks (QSs) suitable for optoelectronic applications around 1.55 μm. The micro-photoluminescence experiments performed on sub-micron mesas at low temperature and low excitation power show several peaks associated to the exciton, biexciton and excited states of single QS, but which present large linewidths in the 0.8–2.5 meV range. The experiments performed through sub-micron apertures on the same bare sample show peaks with narrower linewidths close to 300 μeV. This difference in the linewidth value is thought to be due to a coulomb charge effect induced by the non-intentional doping of the InP barrier layers.

Photonic devices based on 2D PCs have so far been principally targeted at operation in a wave-guided configuration and at providing the basic building blocks for Photonic Integration. The problem of optical losses, which are considered as hindering the operation of 2D photonic integrated circuits based on 2D PC, can be approached from a completely different perspective: instead of attempting to confine the light entirely within waveguide structures, the 2D structures can be deliberately opened to the third space dimension by controlling the coupling between wave-guided and radiation modes. It is shown in this paper that interaction of radiative and guided modes through a photonic crystal, especially under conditions where the later correspond to extrema of the dispersion characteristics of the photonic crystal, results in resonance phenomena which can be used practically for the development of new classes of devices, e.g. combining photonic crystal and MOEMS (Micro Opto Electro Mechanical Systems) structures. We present here the general trends for designing and fabricating PC-MOEMS structures and first experimental results on demonstrators which are now under investigations in our group.

The physical concepts and tools for the extension of 2D Photonic Crystal to out of plane surface operation are presented. The case of the vertical emission Bloch Mode Micro-laser, formed in a 2D Photonic Crystal InP membrane, bonded onto silica on silicon, is emphasized.

Optical properties of a straight 50-row-long photonic crystal waveguide (PCW) are reported. This waveguide is obtained by removing one row of air holes in a triangular lattice two-dimensional photonic crystal etched on a silicon-on-insulator substrate. Transmission measurements are performed on a wide wavelength range (1.15–1.75 μm) with an external white light source. It is found that the experimental data are in very good agreement with both the theoretical transmission calculated by a two-dimensional finite difference time domain method and the theoretical photonic band structure. We show a coupling factor higher than 60% between a monomode ridge waveguide and the PCW.

The general objective of this presentation is to demonstrate the great potential of two dimensional (2D) Photonic Crystals (PC) based on InP-membranes bonded onto silica on silicon substrates, with a special emphasis on the development of various classes of 2D PC microlasers. The basic building block consists in an InP (and related material) membrane including a 2D PC formed by a lattice of holes : the membrane is bonded onto low index material, e .g. silica on silicon substrate, in the prospect of heterogeneous integration with silicon based microelectronics. Examples of devices will be presented, specifically micro-lasers based on 2D PC micro-cavities as well as on 2D in plane and surface emitting Bloch modes (2D Distributed-Feed-Back micro-laser).

Summary form only given. Highly compact microlasers integrated on silicon, emitting in the 1.3-1.6 /spl mu/m range are important building blocks for future photonic integrated circuits that could be developed for applications such as optical interconnects. In-plane emission and low threshold are desirable for these devices, to be compatible with dense photonic integration. In this paper, we report on the fabrication of InP membrane laser micro-sources integrated on a silicon wafer, based on 2D Photonic Crystal (PC) structures. The PC consists of a triangular lattice of holes formed in the thin membrane. The basic integration procedure includes wafer scale InP transfer onto silicon via SiO/sub 2/-SiO/sub 2/ bonding and conventional nanofabrication technologies.

We perform the modelling of a PC waveguide embedded in a membrane with refractive index of 3.2 suspended in air. Due to the index contrast between the membrane and the surrounding air, a good confinement of light inside the membrane is obtained. The 2D PC consists of a triangular lattice of air holes drilled through the membrane. A single line waveguide is obtained by removing a row of first neighbor holes, which introduces an extended linear defect in the periodic structure responsible for the emergence of electromagnetic modes inside the gap. To study the dispersion curves and the spatial distribution of the electromagnetic modes appearing in the waveguide. 3D calculations are necessary to take into account the finite height of the membrane and the occurrence of vertical losses.

The general objective of this presentation is to demonstrate the great potential of InP-membrane photonic devices, witha special emphasis on applications for Optical Communications. Various classes of devices will be presented, which arebased on MOEMS (Micro-Opto-Electro-Mechanical) structures, or 2 dimensional (2D) photonic crystals (PC) or acombination of both, according to a ‘2.5-dimensional’ approach, which should broaden considerably the combinationsof functionality beyond those presently contemplated with the two first classes. For the MOEMS devices, the basicbuilding block consists in a multi-air-gap/suspended-membrane structure, which can be micro-machined using multi-layered III-V semiconductor based heterostructures : tunable filters will be presented for illustration. For PC devices,the basic building block consists in an InP (and related material) membrane including a 2D PC formed by a lattice ofholes : the membrane is either suspended in air or bonded onto low index material, e.g. silica on silicon substrate, in theprospect of heterogeneous integration with silicon based microelectronics. Examples of devices will be presented,specifically micro-lasers based on 2D PC micro-cavities as well as on 2D in plane Bloch modes (2D Distributed-Feed-Back micro-laser). For the ‘2.5-dimensional’ photonic structures, it will be shown that the multi-layer membranapproach, where individual layers or combinations of layers may be structured across to form a 2D PC, is naturallsuitable for this purpose. Examples of devices will be presented (2D PC surface emitting micro-sources, switchingdevices combining vertical MOEMS multi-layer membrane structures and 2D PC).Key words : Indium Phosphide, MOEMS, Photonic Crystals, membrane, Telecommunications, micro-lasers, tunablefilters.

The properties of InAlAs layers grown lattice matched to InP by molecular beam epitaxy (MBE) were investigated. For a large range of growth conditions (temperature, V/III beam equivalent pressure ratio, doping level), we have detected 3 deep electron trap families E1, E2, and E3 in the material bandgap. The presence of these traps give rise to a defect-assisted tunneling current in the space-charge region of Schottky diodes at low forward and reverse biases. The observed low frequency l/fl in reverse bias is interpreted in terms of fluctuations of the Schottky barrier height.

In this work, in order to improve mechanical stability of pseudomorphic HEMTs (PMHEMTs), we propose a pseudomorphic InAlAs/InGaAs/InP structure where the channel and the spacer are strain compensated: as in the conventional structure, the InGaAs channel is compressively strained, but the InAlAs spacer is now tensilely strained. Such a configuration stabilises the whole structure because any strain relaxation in the channel (resp. spacer) should induce an increase of strain in the spacer (resp. channel). In other words, the mechanical state remains metastable but the structure must overcome a higher energy barrier to reach the actual stable state (fully relaxed). Strain compensation has been successfully used previously, in InAsP/lnGaP multi quantum well (MQW) structures for optoelectronic devices. These authors show that a higher number of strained quantum wells can be grown before the appearance of plastic relaxation. In HEMTs, where no MQW is used, an increase of the critical thickness of the channel is expected. In our study, we demonstrate that the use of strain compensation can stabilise PMHEMT structures without spoiling their electrical properties.

In this work, we propose a comparative study of the behaviour of three HEMT structures at high reverse bias: a reference structure (S1) with a conventional InAlAs spacer, the second with an InP/InAlAs mixed spacer (S2) and the third with an In/sub 0.5/Ga/sub 0.5/P/InAlAs (S3) mixed spacer. We show a drastic decrease of the gate leakage current for the mixed spacer HEMTs, thanks to the large valence band offset between InP (or InGaP) and InGaAs. Moreover, Low Frequency Noise (LFN) measurements were performed to investigate the defect distribution in the three structures. These help us to distinguish between the transport mechanisms which govern the gate leakage current.

In this work we present a comparative study of the low frequency noise in different types of HFETs based on an InP substrate. Structures with different barriers (AlInAs, InP or a combination of both) and different channels (InGaAs, InGaAsP and InP) materials were investigated. Also, experiments on plain doped AlInAs and AlGaAs resistors were performed for comparison. This study concentrates on LFN sources induced by the distribution of traps within the different layers and interfaces which constitute the structures, resulting in channel carrier number fluctuations. Experiments were made on structures using a TLM configuration.

Microdisk and photonic crystal (PC) cavity lasers were fabricated on InP based heterostructures integrated on silicon wafers. Single InGaAs quantum well, multiple InGaAs quantum wells and InAs quantum wires are used as active layers. Laser emission is achieved on quantum well based microdisk and PC microcavities. A comparison is made between different combinations of microcavity shapes and active material.

We have investigated light propagation through a single line-defect photonic crystal waveguide on a InP membrane. Modal analysis was performed using the finite-difference time-domain method. The fundamental mode has been found to be very close to the fundamental mode in a “refractive” waveguide but, in this case, it is inherently leaky. The propagation losses of this mode in the complete three-dimensional structure have been computed and measured to determine if its use could be of interest for practical applications. Propagation losses in the range of 0.1 dB/μm have been found numerically and experimentally for the fundamental mode whereas stronger out-of-plane losses have been observed for the other leaky mode within the band gap. The origins of the out-of-plane losses were then investigated and have clarified the inherent lower leakage of the fundamental mode.

Optical properties of two-dimensional photonic crystals (PCs) integrated in a silicon-on-insulator stripe waveguide are reported. Transmission measurements are done on a wide wavelength range (1.1–1.7 μm) by coupling a white-light source in the cleaved edge of the sample and collecting light at the other cleaved side of the waveguide. PC mirrors and one-dimensional (1D) Fabry–Perot cavities formed between two PC reflectors have been fabricated and characterized. The photonic band gap of the mirror is observed in the Γ–M direction for the transverse electric like guided modes. For the waveguide with the 1D Fabry–Perot cavity, resonant modes appear within the gap. It is found that the experimental spectra are in very good agreement with both the theoretical photonic band structure and the theoretical transmission calculated by finite difference time domain.

We present results on the fabrication of optical devices based on photonic crystals on silicon-on insulator substrates. Guides, microcavities, add-drop filters have been obtained with process compatible with CMOS technologies.

We report a study of the optical near field of an active integrated component operating near the 1.55-mum telecommunications wavelength. The device is based on a two-dimensional photonic crystal etched in a suspended InP membrane. Topographic as well as optical information is collected by use of a scanning near-field optical microscope in collection mode, providing information about the local distribution of the losses.

Room temperature pulsed laser operation of 2D photonic crystal microcavities around 1.55 /spl mu/m is reported. Such devices are based on thin III/V heterostructures transferred onto silicon and include an InGaAs/InP multiquantum well (MQW) active layer.

We demonstrate NIR (1.8 micrometer - 2.3 micrometer) resonant photo-detectors based on inter-band (Ecl- Ehhl) absorption in strain compensated, indium rich, InGaAs quantum wells (QW). Extremely low room temperature dark current densities are achieved by reduction of the active layer thickness combined with low defect density of the pseudomorphic strain compensated QWs. The weak absorption of the QW is enhanced by embedding the quantum well into a vertical resonant cavity. We present the experimental results for a demonstrator designed for a wavelength of 2 micrometer. The device, based on a single In 0.83 Ga 0.17 As quantum well and tensile strained barriers for strain compensation, exhibits a selectivity of 9 nm and 18% quantum efficiency. InP/InGaAs and Si/SiO 2 material systems are used for the bottom and top distributed Bragg reflectors (DBR) of the cavity, with 20 pairs and 2 pairs respectively. The semiconductor structure is grown by MOCVD. The top Si/SiO 2 DBR is deposited after fabrication of p-i-n planar photodiodes. Typical dark current densities are lower than 10 -7 A/cm 2 at -2 V bias. Conditions for extension of the operating wavelength up to 2.3 micrometer have been obtained experimentally using InAs/GaAs superlattice deposition to increase the thickness of the strained QW. A prospective tunable detector based on an actuable micro-machined air cavity and air/InP bottom DBR is proposed.

A highly selective selective and tunable optical filter at 1.55 µm using a Fabry-Perot resonator with micromachined InP-air gap distributed Bragg reflectors is developed in our laboratory. In order to optimize the global characteristics of the MOEMS, we have developed an opto-electro-mechanical model. The behavioral model, written in VHDL-AMS-like, allows to simulate each part of this device (electrostatic actuation, mechanical response, optical filtering) separately. Moreover, an integrated simulation, taking into account the interactions between the different parts of the model, is also possible. This model has been implemented into a classical electronic simulator framework, and thus allows the simulation of an entire WDM communication system. The simulated network (STARNET-II-like) consists of four nodes, each one includes an optical filter for the control and a tunable one for the data.

We report on 2D photonic crystal InP membrane micro-lasers transferred onto a silicon wafer. Two types of lasers are investigated: microcavities and defect-free structures, exploiting either conventional defect modes, or DFB-like modes. Room temperature low threshold laser operation has been performed for low sized devices.

Metallic nano-particles or nano-antennas (NAs) provide a strong spatial confinement down to the sub wavelength regime. However, a key challenge is to address and collect light from those nano-scale systems. The tiny active area of the NA is both an advantage for its miniaturization, and a real limit for the level of the collected signal. Therefore, one needs to reconsider how to drive efficiently such NA. Here, we propose to tackle this important issue by designing and realizing a novel nano-optical device based on the use of a photonic crystal cavity (PC cavity) to generate an efficient coupling between the external source and a NA. In this thesis, we design and realize a novel nano-optical device based on the coupling engineering of a photonic crystal (PC) cavity and a nanoantenna (NA). The research work includes nanodevice design, fabrication and characterization. The PC structures are formed in an InP-based membrane with four InAsP quantum wells are in the centre of the membrane to act as an optical gain material of laser mode. The PC structures include defect mode PC structures and Bloch mode PC structures. The bowtie NAs are placed on the backbone of the PC structures. The fabrication of the PC is done by electron beam lithography. Reactive ion beam etching (RIBE) is used to transmit the patterns of PC structures into the InP layer. The NAs are then deterministically positioned on the PC structures by a second e-beam exposure followed by a lift-off process. Overlay measurements showed that the deviation in the alignment error could be as small as 20nm.Optical properties of the hybrid structure are investigated in both far-field and near-field. The far-field measurement shows that the NA increases the lasing threshold of the PC cavity. The wavelength of the laser is also impacted. Near-field scanning optical microscopy (SNOM) has employed to investigate the near-field optical field distribution. The measurement results show that the NA modifies the mode of the structure and localizes the optical field under it. The modification depends on the position and orientation of the NA.

Nous avons realise des microcavites a cristaux photoniques a 2D sur une heterostructure en InP reportee sur silicium. Les proprietes modales de ces structures ont ete etudiees theoriquement et experimentalement, en fonction de la taille de la cavite et du diametre des trous du cristal photonique. Un pompage de ces structures en regime pulse a temperature ambiante a permis d'atteindre une emission laser pour un seuil effectif de l'ordre de 2 mW.

A compact electro-optic modulator on silicon-on-insulator is presented. The structure consists of a III-V microdisk cavity heterogeneously integrated on a silicon-on-insulator wire waveguide. By modulating the loss of the active layer included in the cavity through carrier injection, the power of the transmitted light at the resonant wavelength is modulated; approximately 10 dB extinction ratio and 2.73 Gbps dynamic operation are demonstrated without using any special driving techniques.

Ultralow-power all-optical wavelength conversion is presented for a silicon-on-insulator wire waveguide with a heterogeneously integrated III-V microdisk laser. The principle relies on the suppression of natural lasing from the microdisk laser by an external injection. No probe beam is needed in this configuration. Static wavelength conversion with a control power of 6.4 μW or even lower is achieved. The resonance and gain provided by the microdisk cavity are at the origin of such low control power. Dynamically, wavelength conversion using a 5 Gbps non-return-to-zero bit sequence is demonstrated in the proposed device.

A two-dimensional photonic crystal channel-drop filter is proposed. This device has two high group velocity waveguides that are selectively coupled by a single, low group velocity intermediate waveguide section. It exhibits computed quality factors as high as 1300, and directional dropping efficiencies as high as 90%.

In recent years, many groups have envisioned the possibility of integrating optical and electronic devices in a single chip. In this paper, we study the integration of a photonic crystal laser fabricated in InP with a silicon passive waveguide. The coupling of energy between a 2D photonic crystal (PhC) triangular lattice band-edge laser and waveguide positioned underneath is analyzed in this paper. We show that a 40% coupling could be achieved provided the distance between the laser and the waveguide is carefully adjusted. A general description of the fabrication process used to realize these devices is also included in this paper.

Vertical resonators with a top mirror constituted of 1D photonic crystal membrane on top of a Bragg stack are investigated in this paper. These structures allow the fabrication of compact vertical-cavity surfaceemitting lasers, which can be designed, in addition, for in-plane emission. With this hybrid approach, fabrication problems related to both classical VCSEL and Photonic Crystal lasers may be significantly relaxed, given that a full Bragg stack is replaced by a single photonic crystal membrane and that the Photonic Crystal is not formed in the active gain layer.

New types of switching devices with spatial and spectral resolution combining photonic crystal (PC) and micro-opto-electro-mechanical structures (MOEMS) are proposed. They are based on multilayer suspended high refractive index III–V-based semiconductor membranes, some of these membranes being laterally structured to form a bidimensional PC. We present a method for fabricating these devices implying an original approach that combines micro- and nanotechnologies. The PC is patterned by using electron beam lithography and reactive ion etching. The MOEMS structure is an InP-air gaps multilayer realized by a combination of classical processing of epitaxially grown layers with a selective postprocess micromachining of sacrificial epilayers. Primary demonstrator acting as a wavelength selective and “switchable” coupler including a triangular lattice of PC holes on top of a InP–air gap pair-based Bragg reflector has been realized. We present the preliminary results on the technological fabrication and optical ch...

Graphite-lattice photonic crystal structures in InP-based heterostructures transferred onto silicon, including a multi-quantum well active layer, have been designed and fabricated. 1.5 /spl mu/m vertical emission laser operation was observed at room temperature, with very low threshold (below 50 /spl mu/W).

Microdisk lasers are fabricated in an InP:InGaAs MQW heterostructure transferred onto silicon. The CW room temperature laser operation of such devices at 1.6 /spl mu/m is reported.

Experimental results are presented for a resonant cavity enhanced photodetector operating at 2 µm based on absorption in a single, strain-compensated, In0.83Ga0.17As quantum well. The device exhibits a selectivity of 9 nm, and 18% quantum efficiency. InP/InGaAs and Si/SiO2 material systems are used for the bottom and top Bragg reflectors of the resonant cavity, respectively. The dark current densities are lower than 10-6 A/cm2 at 2 V reverse bias.

Arrays of III-V direct-bandgap semiconductor nanowires are promising candidates for future photovoltaic devices due to their high optical absorption and their ability to be grown on low cost semiconductor substrates like silicon. The core-shell structure is particularly interesting as the electron-hole pair separation occurs in the radial direction and the photogenerated minority carriers have to travel short distances (the radius of the nanowires) thus improving the collection probability in case of well passivated nanowire surfaces. The aim of this study is to find the optimal geometry (length, height and diameter) of a GaAs nanowire array grown on a silicon substrate in order to have the best absorption of the incident photons. For this purpose, we have performed electromagnetic simulations with a homemade Rigorous Coupled Wave Analysis (RCWA) software. Our simulations take into account the core-shell structure, the passivation layer (GaAlAs) and the anti-reflection coating, but also the necessity to achieve current matching between the GaAs nanowire-based and the silicon substrate solar cells. This requirement is justified by the fact that the final goal is to process a tandem solar cell with junctions connected in series.

The realization of mode-locked lasers capable of generating short optical pulses in the near-infrared is a key enabler for various applications including high data rate optical interconnects. The related technology mostly consists of bulky and stand-alone devices, which tends to hinder their widespread use. In addition, the integration of such devices onto chip-based platforms could bring advantages in terms of robustness and stability, while offering some prospects for the realization of advanced hybrid photonic-electronic architectures. There has been recently some progress regarding the miniaturization of fast pulsed lasers [1], but the underlying cavity typically remains longer than a few millimetres and their integration on a chip is still a challenge [2]. Here, we aim at realizing a compact integrated pulsed micro-laser using an innovative photonic crystal (PhC) cavity based on low dispersion slow light modes. Most of the characteristics of mode-locked lasers are tightly linked to the product of the cavity length L and the group index ng of the modes traveling in the cavity. While miniaturization thus tends to degrade the quality of the generated optical pulses, we counterbalance this effect through exploiting slow light (high ng) modes in PhC structures. Dispersion engineering techniques have been successfully developed in passive Si/air suspended PhC cavities for decreasing the otherwise typically high dispersion of these modes [3]. We adapted these techniques to our asymmetric InP/silica structures so as to provide a frequency-equidistant comb of modes - a pre-requisite to laser mode-locking. While our geometry well improves laser heat dissipation with respect to PhC cavities suspended in air, it poses additional constraints and could increase the cavity mode optical losses. Using 3D FDTD simulations, we demonstrated the validity of this approach and designed, as an example, a 30 μm long, linear dispersion PhC cavity, with a group index of 29, providing at least 9 equally-spaced modes over an 11.5 nm bandwidth, which can afford the generation of sub-picosecond optical pulses. Despite the structure asymmetry, quality factors were all above 10,000, i.e. sufficient for reaching laser operation. Compared with a standard strip-waveguide-based laser cavity, this design provides a length reduction factor of almost one order of magnitude, as given by the ratio of the group index of each structure. Various designs enabled us to achieve a range of low dispersion bands with different group index (15-40), offering a relevant trade-off between device miniaturization and short pulse duration. Based on these designs, PhC active structures including InAsP/ InP quantum wells or InAs/InP quantum dashes were fabricated using molecular beam epitaxy, III-V/silica bonding, e-beam lithography and reactive ion etching. Near-field optical microscopy was used to identify both the spectral and spatial signatures of the cavity modes, which were in good agreement with the simulations. We also probed our cavities by microphotoluminescence. These cavities provide a first step towards the realization of miniaturized integrated mode-locked lasers. Their robust hybrid InP/silica geometry offers the potential for integration with silicon photonic devices, while enabling the integration of a saturable absorber, such as graphene, for achieving mode-locked laser operation. References [1] Joshi, S. et al. (2014). Quantum dash based single section mode locked lasers for photonic integrated circuits. Optics Express, 22(9), 11254. [2] Latkowski, S., et al. (2015). Monolithically integrated 25 GHz extended cavity mode-locked ring laser with intracavity phase modulators. Optics Letters, 40(1), 77 [3] Li, J. et al. (2008). Systematic design of flat band slow light in photonic crystal waveguides. Optics Express, 16(9), 6227–6232.

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National audience; Ferroelectrics are a material class characterized by the presence of a spontaneous polarization, which can be switched under electrical and mechanical stimuli. Switching phenomena is a complex process entangled to electronic, chemistry and (micro)structural properties, and intrinsic and extrinsic defects, all these phenomena happening within the ferroelectric object and at its physical boundaries. Considering these phenomena becomes critical in the framework of ferroelectric nanostructures, e.g. integrated thin films, where interfaces and surfaces effects dominate against volume related properties.Here we present the investigation of mechanical and electrical polarization switching on the prototypical tetragonal ferroelectric PbZr0.2Ti0.8O3 (PZT) thin films. Using different routes for chemical solution derived processing and rapid thermal annealing crystallization of epitaxial PZT thin films, we gain control over the electrical properties, chemistry and microstructure of thin films of different thickness. The ferroelectric properties obtained from microcapacitors underline that polarization switching behaviors under electric field are compatible with out-of-plane c-oriented tetragonal PZT, depicting remnant polarization values close to bulk ones for film thickness above 100 nm. Interestingly, a decrease of measured remnant polarization and larger leakage current are observed in capacitors based on films with thickness below 100 nm as well as in those undergoing different crystallization processes. To understand the nanoscale nature of the ferroelectric properties of these films, we used atomic force microscopy (AFM) derived techniques, i.e. piezoresponse force microscopy and local piezoelectric hysteresis loops [1]. Through application of voltage and/or pressure using the AFM-tip, within different electrical boundary conditions, we studied the nucleation and switching phenomena in as grown and in electrically and pressure-induced patterned ferroelectric domains. Results on the coercive electric fields and threshold forces required for polarization switching of PZT films are analyzed in view not only of the different electrical and mechanical poling, but also on the microstructure, film density, defects and chemical composition determined from X-ray diffraction, scanning electron transmission microscopy and electron energy loss spectroscopy, Rutherford backscattering and secondary ion mass spectroscopies.Polarization switching results of PZT films both at the micro- and nano-scales underline that the robust ferroelectric properties and switching mechanisms arise from reproducible chemistry, (micro)structure and defect distribution over thickness in chemical solution derived PZT films. These results will be discussed in the framework of integrated ferroelectric films for nanomechanical applications.

Nano ferroelectricity has promising technological applications as energy-saving, low-sized electronic devices. Tunnel junctions and transistors using ferroelectric gates are examples of potential applications [1]. BaTiO3 (BTO) is a lead-free ferroelectric showing fascinating properties when connected to an electrode, in particular a “positive dead-layer” [2] or interface ionic relaxation [3], making BTO a promising candidate for integration in multifunctional structures with ultimate nanoscale dimensions. For this purpose, the physical and chemical properties of interfaces and ultrathin layers based on BTO have to be understood and means to control their properties must be sought out. In this work, we propose to study ultrathin BTO films grown by industrially scalable magnetron sputtering on conductive Nb-doped SrTiO3 substrates and on structurally compatible conductive layers of SrRuO3, with capping electrodes defining BTO-capacitors, to explore the effect of the conduction and chemical reconstruction phenomena within the films and at the different interfaces.The average structure and strain of BTO films from 2 to 16 nm were investigated using X-ray diffraction. A thorough spectroscopic analysis of the films was carried out to study the relationship between strain and materials and processing parameters. Combining synchrotron X-ray absorption spectroscopy in capacitors and laboratory X-ray photoelectron spectroscopy, we probed the electronic structure under the influence of different UHV annealing conditions, studied the promotion of electronic and ionic defects, e.g. oxygen vacancies. Structural and polarization states of differently strained BTO films were analyzed through X-ray natural linear dichroism at the Ti-L2,3 edges along with multiplet calculations supporting the experimental evidence of the contribution of the strain to the polarization of the films. Scanning transmission electron microscopy and electron energy loss electron spectroscopy provided the atomic scale evidences of the electronic structure through the films and at the interfaces. Combined with piezoresponse force microscopy and electrical characterizations to probe ferroelectric and electrical properties underelectric field, these results are crucial to understand and master the underlying physical mechanisms leading to the ferroelectric properties of operating BTO-based devices.This work is supported by collaborative VOLCONANO ANR-19-CE09-0023 project.[1] Scott, J.F. Science 315, 954 -959 (2007)[2] Stengel, M., Vanderbilt, D. & Spaldin, N.A. Nature Materials 8, 392-397 (2009).[3] Gerra G., Tagantsev A. K., and Setter N., Physical Review Letters 98, 207601 (2007).

National audience

National audience; The discovery of memristor, theorized in 1971 by L. Chua, has led to the development of novel artificial neuromorphic concepts and devices, including ferroelectric-based ones. Ferroelectric Tunnel Junction (FTJ) type memristors based on zirconium-doped hafnium oxide, (HZO), have recently displayed synaptic learning capabilities [1]. In addition, HZO processes are already fully compatible with silicon CMOS industry with oxide layers thinner than 10 nm. In the present work, the HZO layer is realized by room temperature magnetron sputtering of a ceramic target and subsequently crystallized by rapid thermal annealing [2]. The titanium nitride (TiN) bottom (BE) and top (TE) electrodes are realized by reactive magnetron sputtering of a target. We explored the impact of the insertion of an ultra-thin buffer layer at the HZO/TE interface on the stabilized crystalline phase and microstructure, band structure alignment and electrical properties of thin HZO films. We investigated two materials, and . Behind the annealing process and turned into and respectively, following the creation of oxygen vacancies inside the HZO barrier. We exploited X-ray photoemission spectroscopy to analyse the chemistry and the electronic state of the HZO/electrode interface. X-ray reflectometry and grazing incidence X-ray diffraction were used to probe the thickness and structural characteristics of the HZO layer, whose ferroelectricity is associated to the polar orthorhombic phase. We will discuss our results in the framework of structural, chemical and physical properties of the ferroelectric/TE interface and its effect on the electrical properties of thin HZO-based junctions. References: [1] L. Chen et al., “Ultra-low power Hf0.5Zr0.5O2 based ferroelectric tunnel junction synapses for hardware neural network applications,” Nanoscale, vol. 10, no. 33, pp. 15826–15833, 2018, doi: 10.1039/c8nr04734k. [2] J. Bouaziz, P. R. Romeo, N. Baboux, and B. Vilquin, “Huge Reduction of the Wake-Up Effect in Ferroelectric HZO Thin Films,” ACS Appl. Electron. Mater., vol. 1, no. 9, pp. 1740–1745, 2019, doi: 10.1021/acsaelm.9b00367.

International audience; We present a numerical method to accurately model the electrooptic interaction in anisotropic materials. Specifically, we combine a fullvectorial finite-difference optical mode solver with a radio-frequency solver to analyze the overlap between optical modes and applied electric field. This technique enables a comprehensive understanding on how electrooptic effects modify individual elements in the permittivity tensor of a material. We demonstrate the interest of this approach by designing a modulator that leverages the Pockels effect in a hybrid silicon-BaTiO3 slot waveguide. Optimized optical confinement in the active BaTiO3 layer as well as design of travelling-wave index-matched electrodes is presented. Most importantly, we show that the overall electro-optic modulation is largely governed by off-diagonal elements in the permittivity tensor. As most of active electro-optic materials are anisotropic, this method paves the way to better understand the physics of electro-optic effects and to improve optical modulators. (C) 2015 Optical Society of America

International audience