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We report on a GaN/AlGaN quantum cascade detector operating in the terahertz spectral range. The device was grown by metal organic chemical vapor deposition on a c-sapphire substrate and relies on polar GaN/AlGaN step quantum wells. The active region thickness is in micrometer range. The structural, electrical, and optical investigations attest of high structural quality of the synthetized nitride material. The detector exhibits a peak photocurrent at 5.7 THz (23.6 meV) with a responsivity of 0.1 mA/W at 10 K under surface normal irradiation through a 10 μm period grating. The photocurrent persists up to 20 K.

High aspect-ratio etchings are a key aspect of the fabrication of III–V semiconductor devices. The increasing demand for diverse geometries with various characteristic lengths (from the micro- to the nano-meter scale) requires the constant development of new etching recipes. In this article, we demonstrate a versatile mask-plasma combination for micro- and nanofabrication of GaAs substrate using an Inductive Coupled Plasma-Reactive Ion Etching (ICP-RIE) system. We identify five recipes at 25 ° C, with high selectivity, and apply them on one photoresist (AZ4562) and two hard (chromium and nickel) masks. The optimized etching plasma chemistry (BCl 3 /Cl 2 /Ar/N 2 ) shows a pattern transfer on GaAs with a high rate ( ≥ 5.5 μ m/min), a high anisotropy, a high selectivity ( > 4:1 with photoresist mask, and > 50:1 with hard masks), a good etch surface morphology, and smooth sidewalls profile ( > 88 ° ). Herein, we detail the requirements definition, the engineering processes with detailed recipes, the verification, and validation of three device geometries (ridges, cylinders, and nanopillars). The presented results can be valuable for a wide range of applications from the microscale to the nanoscale, and are compatible with a manufacturing process using only a single commercial ICP-RIE tool with two chambers dedicated, respectively, for metallic masks and photoresist mask.

International audience; Silicon detectors are playing a key role in High Energy Physics (HEP) experiments due to their superior tracking capabilities. This study of radiation damage in silicon detectors will give us some insight of changes in the active dopant concentration and how much electrically active carriers are lost after intense radiation exposure. Answering these questions will help us to understand if this loss of active carrier affect the performance of silicon detector used in experiments. This work presents the innovative Transmission Line Model (TLM) method used for the first time to measure the electrically active carrier concentration in silicon detectors. Hence, provide us with another way to study the radiation damage and its effects on the detector performance by studying the variation of the active dopant concentration before and after irradiation.

We report on a GaN/AlN quantum cascade detector operating in an extended spectral range going from the mid-infrared to visible wavelengths. This broadband detection is achieved thanks to the design of active quantum wells supporting five bound-to-bound intersubband transitions. The photodetector exhibits a broad signal between 4.1 μm and 550 nm. The photocurrent persists up to room temperature. The calibrated responsivity at 77 K under irradiation through a 45° angle polished facet amounts to 7 μA/W at a wavelength of 633 nm and is peaked at 14 μA/W at a wavelength of 720 nm.

Motivated by the study of the structure of algebraic actions the additive group on affine threefolds X, we consider a special class of such varieties whose algebraic quotient morphisms X $\rightarrow$ X//Ga restrict to principal homogeneous bundles over the complement of a smooth point of the quotient. We establish basic general properties of these varieties and construct families of examples illustrating their rich geometry. In particular, we give a complete classification of a natural subclass consisting of threefolds X endowed with proper Ga-actions, whose algebraic quotient morphisms $\pi$ : X $\rightarrow$ X//Ga are surjective with only isolated degenerate fibers, all isomorphic to the affine plane A 2 when equipped with their reduced structures.

The development of Zinc Oxide (ZnO)-based applications have been strongly limited due to the lack of reproducible p-type doping. Here we present novel opportunities in the field of unipolar oxide wide band gap semiconductors. First we have developed the growth of nonpolar ZnO/ZnMgO multiple quantum wells (MQWs) and then we demonstrate that the structural and optical properties of the MQWs are reaching the required level for intersubband devices in terms of defects, surface and interface roughness and doping. We will show and discuss the most recent results as, for instance, intersubband transitions which have been observed in such structures. This "Zoterac" project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 665107

Quantum cascade (QC) lasers opens new prospects for powerful sources operating at THz frequencies. Up to now the best THz QC lasers are based on intersubband emission in GaAs/AlGaAs quantum well (QW) heterostructures. The maximum operating temperature is 200 K, which is too low for wide-spread applications. This is due to the rather low LO-phonon energy (36 meV) of GaAs-based materials. Indeed, thermal activation allows non-radiative path through electron-phonon interaction which destroys the population inversion. Wide band gap materials such as ZnO have been predicted to provide much higher operating temperatures because of the high value of their LO-phonon energy. However, despite some observations of intersubband absorption in c-plane ZnO/ZnMgO quantum wells, little is known on the fundamental parameters such as the conduction band offset in such heterostructures. In addition the internal field inherent to c-plane grown heterostuctures is an handicap for the design of QC lasers and detectors. In this talk, we will review a systematic investigation of ZnO/ZnMgO QW heterostructures with various Mg content and QW thicknesses grown by plasma molecular beam epitaxy on low-defect m-plane ZnO substrates. We will show that most samples exhibit TM-polarized intersubband absorption at room temperature linked either to bound-to-quasi bound inter-miniband absorption or to bound-to bound intersubband absorption depending on the Mg content of the barrier material. This systematic study allows for the first time to estimate the conduction band offset of ZnO/ZnMgO heterostructures, opening prospects for the design of QC devices operating at THz frequencies. This was supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement #665107.

We report an extraction-controlled terahertz (THz)-frequency quantum cascade laser design in which a diagonal LO-phonon scattering process is used to achieve efficient current injection into the upper laser level of each period and simultaneously extract electrons from the adjacent period. The effects of the diagonality of the radiative transition are investigated, and a design with a scaled oscillator strength of 0.45 is shown experimentally to provide the highest temperature performance. A 3.3 THz device processed into a double-metal waveguide configuration operated up to 123 K in pulsed mode, with a threshold current density of 1.3 kA/cm2 at 10 K. The QCL structures are modeled using an extended density matrix approach, and the large threshold current is attributed to parasitic current paths associated with the upper laser levels. The simplicity of this design makes it an ideal platform to investigate the scattering injection process.

We demonstrate two-dimensional arrays of surface-emitting THz frequency photonic-crystal quantum cascade lasers covering a broad spectral range. The arrays are made of 16 unit elements, each of them spectrally single mode and featuring a narrow divergence emission pattern. The array emission frequencies cover a range of ≈0.2 THz around an emission frequency of ≈2.75 THz. Large size and small size devices have been developed. The former devices operate up to a maximum temperature of ≈90K with 2 to 3 mW output power in continuous wave regime.

Etched multilayers obtained by forming a laminar grating pattern within interferential multilayer mirrors are used in the soft X-ray range to improve the spectral resolution of wavelength dispersive spectrometers equipped with periodic multilayers. We describe the fabrication process of such an etched multilayer dispersive element, its characterization through reflectivity measurement and simulations, and its implementation in a high-resolution Johann-type spectrometer. The specially designed patterning of a Mo/B4C multilayer is found fruitful in the range of the C K emission as the diffraction pattern narrows by a factor 4 with respect to the non-etched structure. This dispersive element with an improved spectral resolution was successfully implemented for electronic structure study with an improved spectral resolution by X-ray emission spectroscopy. As first results, we present the distinction between the chemical states of carbon atoms in various compounds, such as graphite, SiC and B4C, by the different shape of their C K emission band. Copyright © 2012 John Wiley & Sons, Ltd.

This paper deals with the conception and realization of a 3 axis gyrometer in GaAs known as CVG (Coriolis Vibrating Gyro), designed thanks to MEMS (Micro Electro Mechanical Systems) technologies. This original 3 axis gyroscope [1] can measure angular rate along the 3 sensing axes using the Coriolis inertial force effect on a single vibrating structure and is particularly well suited for applications where high miniaturization/integration and low consumption are required as attitude control of micro-UAVs (micro-Unmanned Aerial Vehicles) for instance. The proposed design shows important sensibilities along the 3 orthogonal directions. In automotive, aerospace and aeronautical industries, there is an increasing demand for accurate detection of acceleration and angular rate. Usually, objects are in motion in a three-dimensional space. To determine with precision the motion of an object, it is necessary to detect acceleration and angular rate in each of the three different space directions. A common way for multi-axial detection is to use a set of three different mono-axial sensors aligned with each of the three axial directions. Although miniaturized single axis gyroscopes have now reached high performances, 3 axis gyroscopes based on the combination and alignment of such single gyroscopes usually have lower performances than a fully integrated triaxial device because of alignment accuracy. In addition the alignment procedure is typically expensive. That is why, since several years, there is a rising need for monolithic 3 axis gyroscopes for angular rate detection. In this paper we investigate a 3 axis monolithic GaAs CVG structure that allows a single “driving mode” for the three “sensing modes”. This allows: — a reduction of mechanical coupling between the “driving mode” and the “sensing modes” — an easier fabrication owing to a simplified electrode network. — a less complex ASIC (Application Specific Integrated Circuit) design having a smaller size and a lower power consumption. Various designs of 3 axis gyro have been proposed in the literature but few of them show good and equivalent sensitivities along the three sensing axis. In the first section we will examine two interesting designs of CVG selected among published works which also use a single driving mode and three sensing modes. In the second section we described a design that we proposed previously and that has potentially much higher performances. Then we will investigate how GaAs piezoelectricity can be used to build a complete piezoelectric transduction system for this CVG. In the last section, we will give an overview of the transduction system design and of its fabrication process. Finally we will report results of the development of GaAs Deep Reactive Ion Etching (DRIE) which is major step of this fabrication process.

This article studies the group generated by automorphisms of the projective space of dimension $n$ and by the standard birational involution of degree $n$. Every element of this group only contracts rational hypersurfaces, but in odd dimension, there are simple elements having this property which do not belong to the group. Geometric properties of the elements of the group are given, as well as a description of its intersection with monomial transformations.

We present the determination of the index variation in the GaN/AlN heterostructures related to the population/depletion of the quantum wells fundamental state leading to the intersubband (ISB) absorption variation in the spectral domain around 1.5μm. The experiments were performed using wide-strip waveguide structure. It is shown that the determination of the refraction index in a wide-strip structure is possible when the waveguide is multimode in the vertical direction with a small number of higher order modes. The variation of the refractive index is then deduced from the shift of the position of the beating interference maxima of different order modes. The obtained index variation with bias from complete depletion to full population of the quantum wells is around -5×10-3. This value is similar to the typical index variation achieved in InP and is an order of magnitude higher than the index variation obtained in silicon. The remarkable feature is that maximum index variation is obtained at the wings of the ISB transition line where absorption is reduced with respect to the peak value. This index variation mechanism opens prospects for the realization of ISB phase modulators by inserting the active region in a Mach-Zehnder interferometer.

dimensions as small as λeff/9 in all directions of space (or λ/30 with the vacuum wavelength). We experimentally prove that the capacitance and inductance of these devices are not interdependent, as in purely photonic cavities, but that they can be adjusted almost independently, as in an electronic circuit. This functionality proves that the dimensions of these hybrid electronic-photonic devices are intrinsically not limited by diffraction as in conventional photonic resonators. Using arguments from transmission line theory, we show that it is necessary to include at least one metallic loop in the cavity design to access this regime and we note, as a corollary, that some recent proposals to miniaturize THz resonators and devices beyond the diffraction limit do not meet this fundamental requirement. Our results shed a light on the ability to describe THz/metallic cavities in terms of circuit elements. Furthermore, upon insertion of electrical contacts, these extremely subwavelength resonators can potentially lead to advances in THz detectors and phased array antennas.

This paper reviews the recent progress towards III-nitride in tersubband devices based on quantum wells. We first present recent achievements in terms of GaN-based quantum cascade detectors operating at near-infrared wavelengths. We show that these devices are intrinsically extremely fast based on femtosecond time-resolved measurements of the photocurrent. The design of III-nitride quantum cascade detectors, which relies on the engineering of the internal electric field, is flexible enough to allow for two-color detection. We finally discuss the potential of III-nitride intersubband devices in the THz frequency domain a nd present the recent observ ation of THz absorption using low aluminium content AlGaN/GaN step quantum wells. Keywords: III-nitride semiconductors, intersubband transitions, optoelectronic devices, quantum cascade detectors, quantum wells. INTRODUCTION Intersubband photonics (ISB) have emerged within the last 25 years and led to a number of fascinating control-by–design devices relying on the quantum engineering of electron confinement in semiconductor quantum wells (QW) or quantum dots (QD) [1]. One famous example is the quantum cascade laser (QCL), which was invented in the mid-90’s at Bell Laboratories [2]. This device relies on the repetition of multiple quantum well (MQW) active regions where ISB light emission takes place and injector/extractor regions to transfer electrons from one period to the other. The ISB emission wavelength can be tuned in a wide spectral range simply by adjusting the layer thickness. Using materials such as GaAs/AlGaAs, InGaAs/AlInAs or antimonides, the operation wavelength of ISB devices such as the QCLs can be tuned from the mid-infrared to the THz spectral range. Operation at short wavelengths is limited by the available conduction band offset and by the material transparency. Thanks to the progress achi eved in terms of epitaxial growth of ultrathin layers, III-nitride semiconductors (GaN, AlN, InN and their alloys) have emerged within the last ten years as excellent materials for ISB photonics devices in the near-infrared spectral range and in particular in the 1.3-1.55 µm wavelength window used for fibre optics telecommunications. Not only they are transparent in a wide spectral region (360 nm to 13 µm for GaN) but the conduction band offset prov ided by their heterostructures is quite large, of the order of 1.75 eV for GaN/AlN [3]. In contrast to InAs/AlSb materials, which also exhibit a large conduction band discontinuity, the remote valleys of GaN lie very high in energy (>2 eV above the + point [4]), offering the potential for ISB light emitting devices at record short near-infrared wavele ngths. Another specificity of nitride materials is the large longitudinal-optical (LO) phonon energy (92 meV for GaN) as well as the presence of huge internal fields induced by the spontaneous and piezoelectric polarizatio ns along the c axis inherent to their wu rtzite structure. The presence of these

International audience; Fretting damage appears in quasi-static mechanisms submitted to small amplitude oscillatory motion. Depending on the amplitude of displacement, it could lead to catastrophic failure in many industrial applications due to crack initiation or wear damage. To reduce the damage caused by fretting, an increasing use of coatings and surface treatments has been made. In service, the grooves in cryogenic (liquid hydrogen) turbopump shaft in Ti6Al4V can be damaged, a Cu-Ni-Si P.V.D. coating has solved the problem. New diamond-like-carbon (DLC) coatings with interesting tribological properties seem to be attractive for solving industrial problems. The present study analyses the behaviour of plasma nitrided Ti6Al4V with or without a DLC layer. Its effect on crack initiation resistance will be characterised for TI6Al4V substrate. The increase of load capacity due to the treatments will be evaluated in a cryogenic environment.

Elastomeric matrix composites (EMCs) subjected to static and fluctuating loads basically fail due to the nucleation and growth of defects. Also, high hydrostatic pressure can influence the mechanical behaviour of EMCs. The change in behaviour of EMCs due to the nucleation of cavitations under hydrostatic pressure is studied here to understand the mechanics underlying the damage mechanism. Two types of materials for pancake specimens are used in this study; natural rubber (NR) vulcanized and reinforced by carbon black and synthetic rubber (styrene-butadiene-rubber, SBR). In situ observations of uniaxial tension and torsion tests are also presented by using X-ray computed tomography (CT) (medical scanner) and the results are compared with those from scanning electron microscopy (SEM).

1 - Article; RésuméObjectifs Comparer deux techniques de préparation d'échantillons pour l'observation en microscopie électronique à balayage à pression variable (MEB-PV) afin d'évaluer la colonisation cellulaire et tissulaire de ligaments artificiels explantés.Matériels et méthodes Des ligaments artificiels en PET et PET greffé par un polymère bioactif, le poly(styrène sulfonate de sodium) ont été implantés dans le genou de quatre brebis après section du ligament croisé antérieur (LCA) puis explantés trois mois plus tard. L'évaluation qualitative de la colonisation cellulaire et tissulaire des ligaments artificiels a été réalisée sur des explants séchés (MEB-PV) ou non (MEB-PV-Peltier) au point critique.Résultats et discussion Les deux techniques évaluées ont permis de mettre en évidence des différences dans la bio-intégration des deux types de ligaments étudiés. Seule la technique MEB-VP-Peltier a permis l'obtention d'images d'excellente définition à fort grossissement se montrant à ce titre très intéressante pour l'évaluation qualitative rapide de l'intégration cellulaire et tissulaire des ligaments artificiels.Objectives We carried out a comparative study between two methods to prepare explanted artificial ligaments samples before their observation in the variable pressure scanning electron microscope (VP-SEM).Materials and methods Poly(ethylene terephtalate) (PET) artificial ligaments grafted by a bioactive polymer, the poly(sodium styrene sulfonate) were implanted for three months in the knee of four ewes after section of the anterior cruciate ligament (ACL). The qualitative evaluation of the cellular and tissue colonization of the artificial ligaments was carried out on critical point-dried explants (observed by VP-SEM) or not (observed by VP-SEM-Peltier).Results and discussion The results showed differences in the biointegration of the two types of studied ligaments. Only the MEB-VP-Peltier technique allowed obtaining images of excellent resolution with high magnification. For this reason the MEB-VP-Peltier technique is a promising method for the fast qualitative evaluation of the cellular and tissue integration of the artificial ligaments.

The objective of this study was to evaluate the buckling phenomenon as a typical defect affecting sheet metal forming procedures of interstitial free (IFS) sheet steels used in automotive industry. The occurrence of the buckling in sheet metal forming is an important problem for efficient press shop operations. The initiation and growth of these defect depends on different parameters such as mechanical properties of the sheet materials, stress ratio, geometry of the pieces, etc. In this paper, a modified Yoshida buckling test is presented as an improved and more reliable buckling test in order to determine the buckling limit diagrams (BLDs) of IFS when ranking the formability of sheet metals. The finite element analysis (FEA) is carried out for the modified Yoshida buckling test and compared with the experimental results.

We demonstrate efficient surface-emitting terahertz frequency quantum cascade lasers with continuous wave output powers of 20–25 mW at 15 K and maximum operating temperatures of 80–85 K. The devices employ a resonant-phonon depopulation active region design with injector, and surface emission is realized using resonators based on graded photonic heterostructures (GPHs). GPHs can be regarded as energy wells for photons and have recently been implemented through grading the period of the photonic structure. In this paper, we show that it is possible to keep the period constant and grade instead the lateral metal coverage across the GPH. This strategy ensures spectrally single-mode operation across the whole laser dynamic range and represents an additional degree of freedom in the design of confining potentials for photons.

We report on ultrafast GaN/AlGaN waveguide quantum cascade detectors with a peak detection wavelength of 1.5 μm. Mesa devices with a size of 7 × 7 and 10 × 10 μm2 have been fabricated with radio-frequency impedance-matched access lines. A strong enhancement of the responsivity is reported by illuminating the waveguide facet, with respect to illumination of the top surface. The room temperature responsivity is estimated to be higher than 9.5 ± 2 and 7.8 ± 2 mA/W, while the −3dB frequency response is extracted to be 42 and 37.4 GHz for 7 × 7 and 10 × 10 μm2 devices, respectively.

In this work, we have investigated the vertical electron transport through a seven-period GaN/AlN multiple-quantum-well structure. The devices show asymmetric current–voltage characteristics displaying negative differential resistance at room temperature. These features persist for multiple scans and are reproducible for both upward and downward sweeping voltages. We interpret the negative differential resistance as a consequence of the resonant tunneling between the fundamental and excited states of adjacent quantum wells. The experimental results are in good agreement with the predictions of an electron transport simulation.

We demonstrate semiconductor terahertz (THz) resonators with sub-wavelength dimensions in all three dimensions of space. The maximum confinement is obtained for resonators with a diameter of 13 μm, which operate at a wavelength of ≈272 μm. This corresponds to a λeff/6 confinement, where λeff is the wavelength inside the material (or λ/20, if the free space wavelength is considered). These highly sub-wavelength devices operate on the fundamental magnetic resonance, which corresponds to the fundamental oscillation mode of split-ring resonators and is usually inactive in purely optical resonators. In this respect, these resonators are another step towards the hybridization of optics and electronics at THz frequencies. As a proof of principle for cavity quantum electrodynamics experiments, we apply these resonators to THz intersubband polaritons.

The effect of the temperature on the electrical characteristics in GaN-based resonant tunneling diodes is studied both theoretically and experimentally. At room temperature, the current-voltage measurements show reproducible negative differential resistances and a current hysteresis. However these features disappear when the temperature is decreased down to 100 K. In addition, the current exhibits transients over a few tenths of seconds which effect disappears at low temperatures. Based on these results, we conclude that the observed negative differential resistance at room temperature is not due to electron resonant tunneling but to trap charging and release.

Demonstrated is a GaN/Al(Ga)N quantum cascade detector operating at room temperature with a peak detection wavelength of 1.5 m, which is the shortest value ever reported for such a device in any material system. The 3 dB detection spectral range spans from 1.37 to 1.57 m wavelength. The calibrated peak responsivity for TM-polarised light is measured to be around 15 V/W at room temperature.

We investigate the parameter optimization for micron-scale etching by Inductive Coupled Plasma - Deep Reactive Ion Etching (ICP-DRIE) of GaAs/AlGaAs semiconductor heterostructures. Although dry etching approaches have been reported in the literature using a broad variety of plasma etch tools, there is still need to meet the majority of microsystems dry etching requirements. The etch process family studied here, is dominated by the relative pressures of BCl3 (Boron trichloride) and Cl2 (Chlorine) gases. The influence of using a BCl3/Cl2/Ar/N2 mixture at different pressures has been investigated: A small addition of N2 (Nitrogen) is very effective inducing sidewall protection when using photoresist masks. The etch profile quality has been characterized as a function of the plasma process and of the etched feature sizes. The desired etch characteristics for GaAs/AlGaAs heterostructures can be achieved by controlling the various process parameters with good reliability, high selectivity, and – simultaneously – high etch rates and sidewall verticality. Etch rates from 1 to over 5.5 μm/min have been obtained. The selectivity with optical photoresist varies from 2.3 to 16. The presented results can be valuable for a wide range of applications involving fabrication of micro-electro-mechanical-systems or Micro Optoelectronic Mechanical Systems.

We demonstrate semiconductor resonators operating on the fundamental monopolar resonance which corresponds to the fundamental oscillation mode of split-ring resonators. Their size is considerably below the optical diffraction limit in all three dimensions of space. The maximum confinement is obtained for resonators operating at a wavelength of λ ∼ 272 μm (v ∼ 1.1 THz): they have a diameter of 13 μm and a thickness of 1 μm. This corresponds to a X eff /6 confinement in all 3 directions of space (X eff is the wavelength inside the material). As a proof-of-principle of cavity-QED application, we employ these resonators for intersubband polaritonics.