InAs/GaAs quantum-dot superluminescent light-emitting diode monolithically grown on a Si substrate

Building optoelectronic devices on a Si platform has been the engine behind the development of Si photonics. In particular, the integration of optical interconnects onto Si substrates allows the fabrication of complex optoelectronic circuits, potentially enabling chip-to-chip and system-to-system optical communications at greatly reduced cost and size relative to hybrid solutions. Although significant effort has been devoted to Si light generation and modulation technologies, efficient and electrically pumped Si light emitters have yet to be demonstrated. In contrast, III–V semiconductor devices offer high efficiency as optical sources. Monolithic integration of III–V on the Si platform would thus be an effective approach for realizing Si-based light sources. Here, we describe the first superluminescent light-emitting diode (SLD) monolithically grown on Si substrates. The fabricated two-section InAs/GaAs quantum-dot (QD) SLD produces a close-to-Gaussian emission spectrum of 114 nm centered at 1255 nm wavelength, with a maximum output power of 2.6 mW at room temperature. This work complements our previous demonstration of an InAs/GaAs QD laser directly grown on a Si platform and paves the way for future monolithic integration of III–V light sources required for Si photonics

1.7eV Al0.2Ga0.8As solar cells epitaxially grown on silicon by SSMBE using a superlattice and dislocation filters

Lattice-mismatched 1.7eV Al0.2Ga0.8As photovoltaic solar cells have been monolithically grown on Si substrates using Solid Source Molecular Beam Epitaxy (SSMBE). As a consequence of the 4%-lattice-mismatch, threading dislocations (TDs) nucleate at the interface between the Si substrate and III-V epilayers and propagate to the active regions of the cell. There they act as recombination centers and degrade the performances of the cell. In our case, direct AlAs/GaAs superlattice growth coupled with InAlAs/AlAs strained layer superlattice (SLS) dislocation filter layers (DFLSs) have been used to reduce the TD density from 1×10^9cm^-2 to 1(±0.2)×10^7cm^-2. Lattice-matched Al0.2Ga0.8As cells have also been grown on GaAs as a reference. The best cell grown on silicon exhibits a Voc of 964mV, compared with a Voc of 1128mV on GaAs. Fill factors of respectively 77.6% and 80.2% have been calculated. Due to the lack of an anti-reflection coating and the non-optimized architecture of the devices, relatively low Jsc have been measured: 7.30mA.cm^-2 on Si and 6.74mA.cm^-2 on GaAs. The difference in short-circuit currents is believed to be caused by a difference of thickness between the samples due to discrepancies in the calibration of the MBE prior to each growth. The bandgap-voltage offset of the cells, defined as Eg/q-Voc, is relatively high on both substrates with 736mV measured on Si versus 572mV on GaAs. The non-negligible TD density partly explains this result on Si. On GaAs, non-ideal growth conditions are possibly responsible for these suboptimal performances

Defect-Free Self-Catalyzed GaAs/GaAsP Nanowire Quantum Dots Grown on Silicon Substrate

The III-V nanowire quantum dots (NWQDs) monolithically grown on silicon substrates, combining the advantages of both one- and zero-dimensional materials, represent one of the most promising technologies for integrating advanced III-V photonic technologies on a silicon microelectronics platform. However, there are great challenges in the fabrication of high-quality III-V NWQDs by a bottom-up approach, that is, growth by the vapor-liquid-solid method, because of the potential contamination caused by external metal catalysts and the various types of interfacial defects introduced by self-catalyzed growth. Here, we report the defect-free self-catalyzed III-V NWQDs, GaAs quantum dots in GaAsP nanowires, on a silicon substrate with pure zinc blende structure for the first time. Well-resolved excitonic emission is observed with a narrow line width. These results pave the way toward on-chip III-V quantum information and photonic devices on silicon platform

Monolithically Integrated InAs/GaAs Quantum Dot Mid-Infrared Photodetectors on Silicon Substrates

High-performance, multispectral, and large-format infrared focal plane arrays are the long-demanded third-generation infrared technique for hyperspectral imaging, infrared spectroscopy, and target identification. A promising solution is to monolithically integrate infrared photodetectors on a silicon platform, which offers not only low-cost but high-resolution focal plane arrays by taking advantage of the well-established Si-based readout integrated circuits. Here, we report the first InAs/GaAs quantum dot (QD) infrared photodetectors monolithically integrated on silicon substrates by molecular beam epitaxy. The III–V photodetectors are directly grown on silicon substrates by using a GaAs buffer, which reduces the threading dislocation density to ∼106 cm–2. The high-quality QDs grown on Si substrates have led to long photocarrier relaxation time and low dark current density. Mid-infrared photodetection up to ∼8 μm is also achieved at 80 K. This work demonstrates that III–V photodetectors can directly be integrated with silicon readout circuitry for realizing large-format focal plane arrays as well as mid-infrared photonics in silicon

On the similarity of Sturm-Liouville operators with non-Hermitian boundary conditions to self-adjoint and normal operators

We consider one-dimensional Schroedinger-type operators in a bounded interval with non-self-adjoint Robin-type boundary conditions. It is well known that such operators are generically conjugate to normal operators via a similarity transformation. Motivated by recent interests in quasi-Hermitian Hamiltonians in quantum mechanics, we study properties of the transformations in detail. We show that they can be expressed as the sum of the identity and an integral Hilbert-Schmidt operator. In the case of parity and time reversal boundary conditions, we establish closed integral-type formulae for the similarity transformations, derive the similar self-adjoint operator and also find the associated "charge conjugation" operator, which plays the role of fundamental symmetry in a Krein-space reformulation of the problem.Comment: 27 page

Splitting Arabic Texts into Elementary Discourse Units

International audienceIn this article, we propose the first work that investigates the feasibility of Arabic discourse segmentation into elementary discourse units within the segmented discourse representation theory framework. We first describe our annotation scheme that defines a set of principles to guide the segmentation process. Two corpora have been annotated according to this scheme: elementary school textbooks and newspaper documents extracted from the syntactically annotated Arabic Treebank. Then, we propose a multiclass supervised learning approach that predicts nested units. Our approach uses a combination of punctuation, morphological, lexical, and shallow syntactic features. We investigate how each feature contributes to the learning process. We show that an extensive morphological analysis is crucial to achieve good results in both corpora. In addition, we show that adding chunks does not boost the performance of our system

Study of the 26Al(n,p)26Mg and 26Al(n,α)23Na reactions using the 27Al(p,p')27Al inelastic scattering reaction

26Al was the first cosmic radioactivity ever detected in the galaxy as well as one of the first extinct radioactivity observed in refractory phases of meteorites. Its nucleosynthesis in massive stars is still uncertain mainly due to the lack of nuclear information concerning the 26Al(n,p)26Mg and 26 Al(n,α)23Na reactions. We report on a single and coincidence measurement of the 27Al(p,p')27Al(p)26Mg and 27Al(p,p')27Al(α)23Na reactions performed at the Orsay TANDEM facility aiming at the spectroscopy study of 27Al above the neutron threshold. Fourteen states are observed for the first time within 350 keV above the 26Al+n threshold

Diversité des pratiques d'élevage bovin à viande dans le massif du Dahra (Algérie)

Pour appréhender la diversité des pratiques d’élevage bovin à viande dans les zones rurales du massif du Dahra (nord-ouest algérien), une typologie a été réalisée à partir des résultats d’une enquête dans 56 exploitations. Les groupes définis diffèrent par les structures et sont de 5 types (A, B, C, D et E). L’analyse technico - économique de 20 exploitations réparties sur les différents types préalablement identifiés révèle 4 systèmes de pratiques différents selon l’objectif de production, le plus souvent en cohérence avec les structures disponibles. Le contrôle des performances réalisé au niveau de 9 exploitations montre que lorsqu'on exclut le système d’élevage bovin commercial sans femelles reproductrices (engraisseur), le système à logique de capitalisation apparaît alors comme le plus performant

Effects of Series Resistance and Frequency on the Capacitance/ Conductance –Voltage C/G-V Characteristics of Au/GaN/GaAs and Au/GaAs Diodes

Link to publisher's homepage at http://ijneam.unimap.edu.myIn order to analyze the effect of the presence of the GaN layer and series resistance, the electrical characteristics of the Au/GaAsand Au/GaN/GaAsdiodes are investigated. The study is realized by a nitridation process of GaAs substrates. The GaN layer is growth in ultrahigh vacuum system with annealing operation realized at 620°C during one hour. (CV) and (G-V) characteristics of Au/GaN/GaAs and Au/GaAs nanostructures at different frequencies have been studied. The estimated values of Rs showed a regular diminution. Since Rs causes errors in the extraction of electrical parameters. Consequently, the measured capacitance (C-V) and conductance (G-V) are corrected to obtain the real “corrected” capacitance (Cc-V) and (Gc-V) of the diodes. Thus, one showed clearly that the values of Cc and Gc increased proportionally with the applied bias voltage. This effect can be observed practically in the accumulation region and for a high frequency (1 MHz). From the C-2-V curves and after correction, the diffusion potential Vd is evaluated to (0.32 V -0.25 V) and the potential barrier φbn is estimated equal to 0.38 eV and 0.31eV for Au/GaN/GaAs and Au/GaAs structures respectively. The states densities Nss for Au /GaN/GaAs and Au/GaAs structures are determined at (Ec-0.2) with and without series resistances and are found equal to (7.3×1012 eV-1 cm-2 and 6.1×1010 eV-1 cm-2) and (9.31×1010 eV-1 cm-2 and 1010 eV-1 cm-2) respectively

Preparation and characterization of activated coal from bitter almond shells (Prunus amygdalus) = Préparation et caractérisation d’un charbon actif à partir de la coquille d’amande (Prunus amygdalus) amère

Description of the subject. The present study concerns the preparation of activated coal (AC) from bitter almond (Prunus amygdalus) shells (BASh), a fruit that grows spontaneously in the Setif region (northeast Algeria). Obtaining and characterizing activated coal was the valorization method adopted here. Objectives. The aim of this study was to elucidate the feasibility of the chemical activation of BASh in order to obtain two types of activated coal (AC). Method. The two ACs were obtained from BASh by acid (CAa) and basic (CAb) activation. The final products were investigated for their different physicochemical characteristics: angle of repose, ash, differential screening calorimetry, etc. In the case of CAa, the modeling of the adsorption kinetic of methylene blue (MB), as well as of adsorption isotherms, was also performed. Results. The activation mode seemed to affect unequally the different physicochemical