Efficient JPEG 2000 Image Compression Scheme for Multihop Wireless Networks

 When using wireless sensor networks for real-time data transmission, some critical points should be considered. Restricted computational power, reduced memory, narrow bandwidth and energy supplied present strong limits in sensor nodes. Therefore, maximizing network lifetime and minimizing energy consumption are always optimization goals. To overcome the computation and energy limitation of individual sensor nodes during image transmission, an energy efficient image transport scheme is proposed, taking advantage of JPEG2000 still image compression standard using MATLAB and C from Jasper. JPEG2000 provides a practical set of features, not necessarily available in the previous standards. These features were achieved using techniques: the discrete wavelet transform (DWT), and embedded block coding with optimized truncation (EBCOT). Performance of the proposed image transport scheme is investigated with respect to image quality and energy consumption. Simulation results are presented and show that the proposed scheme optimizes network lifetime and reduces significantly the amount of required memory by analyzing the functional influence of each parameter of this distributed image compression algorithm.

Effect of Piezoelectric Filed on the Optical Properties of (311) A and (311) B Oriented InAlAs/InP Heterostructures

InAlAs alloy was grown by MOCVD on an InP (311) substrate with different polarities. Measurements of photoluminescence (PL) and photoreflectance (PR) were performed to study the impact of the V/III flux ratio. It is discovered that the PL line was shifted to a greater energy side with the increasing excitation power density, and no saturation was observed of its related PL intensity. It is a fingerprint of type II transition emission. However, the recombination of the type II interface showed a powerful dependence on AsH3 overpressure and substrate polarity. In fact, we have noted an opposite behavior of type II energy transition shift from A to B polarity substrate in respect to V/III ratio variation. PR signals corresponding to Franz-Keldysh Oscillation (FKO) were observed. The analysis of their period has allowed one to assess the value of the PZ field in the samples. PL-luminescence measurements were performed out as a function of temperature. PL peak energy, PL intensity, and half maximum full width show anomalous behaviors. Indicating the existence of localized carriers, they were ascribed to the energy potential modulation associated with the indium cluster formation and PZ field

Time resolved and temperature dependence of the radiative properties of thiol-capped CdS nanoparticles films

In this work, we present the temperature-dependence and time-resolved photoluminescence (PL) of CdS nanoparticles capped independently with three different ligands thiophenol, thioglycerol, and l-cysteine over a broad temperature range from 10 to 300 K. The respective nanoparticles sizes in the three systems studied in this work are 1.5, 4, and 2 nm as determined from X-ray diffraction (XRD). From the analysis of AFM images, it was found that the lateral particle sizes of capped CdS nanoparticles are greater than those deduced from XRD or optical absorption measurements. The aim of this study is the investigation of the impact of the organic ligands on the radiative recombination dynamics in organically capped CdS nanoparticles. From the PL study and based on the temperature-dependence and time-resolved emission spectroscopy, we conclude that the emission of CdS QDs film originates from recombination of the delocalized carriers in the internal core states with a small contribution of the localized carriers at the interface. The PL decay reveals a biexponential behavior for the entire three samples at all temperatures. One of the two exponential components decays rapidly with a time τ(1) in the range 0.5–0.8 ns, whereas the other decays much more slowly, with a time τ(2) in the range 1–3 ns. The weak activation energy (32–37 meV) deduced from the temperature dependence of the PL intensity suggests the involvement of shallow traps. The analysis of the experimental results reveals a relatively narrow size distribution, an efficient surface passivation, and a satisfactory thermal stability of CdS nanocrystals

Optical properties of self-assembled InAs quantum islands grown on InP(001) vicinal substrates

International audienceWe have investigated the effect of misorientated InP001 substrates on the optical properties of InAs quantum islands QIs grown by molecular-beam epitaxy in the Stranski-Krastanow regime. Detailed temperature-dependent photoluminescence PL, excitation density PL, and polarization of photoluminescence PPL are studied. PPL shows a high degree of linear polarization near 40% for the nominally oriented substrate n and for the substrate with 2° off miscut angle toward the 110 direction (2° F), while it is near 15% for the substrate with 2° off miscut angle towards 010 direction (2° B), indicating the growth of InAs quantum wires on nominal and 2° F substrates and of InAs quantum dots on 2° B substrate. These island shapes are confirmed by morphological investigations performed by atomic force microscopy. The integrated PL intensity remains very strong at room temperature, as much as 36% of that at 8 K, indicating a strong spatial localization of the carriers in the InAs QIs grown on InP001

Etude des défauts électriquement actifs dans les composants hyperfréquences de puissance dans les filières SiC et GaN

La demande croissante de composants permettant d'opérer à de fortes puissances, à hautes fréquences et à hautes températures a conduit au développement de filières électroniques à base de semiconducteurs à large bande interdite tels que le nitrure de galium (GaN) et le carbure de silicium (SiC). Toutefois, la maîtrise encore imparfaite des matériaux en termes des défauts au sens large (impuretés, défauts cristallins) limite les performances des dispositifs à base de SiC et GaN. Dans ce travail de thèse, nous nous sommes partculièrement intéressé à l'étude de deux dispositifs : les transistors MESFETs 4H-SiC et les HEMTs A1GaN/GaN/Si destinés à des applications hyperfréquences et puissance. L'étude des caractéristiques des sorties statiques de ces deux composants a révélé certains dysfonctionnements. Pour les MESFETs 4H-SiC, un effet d'hystérésis sur la conductance drain-source en fonction du sens du balayage de la tension de grille, un effet de kink et un décalage de la tension de seuil ont été mis en évidence. Une étude de défauts utilisant notamment la DLTS et la CDLTS, nous a permis de montrer que ces effets sont dus à la présence de défauts profonds dans la structure. Pour les HEMTs A1GaN/GaN sur substrat de silicium (Si), un effet d'hystérésis, ainsi qu'un effet d'auto-échauffement ont été observés. Les mesures de CDLTS avec des impulsions sur le drain ont permis de mettre en évidence la présence de défauts étendus (dislocations) décorés par des pièges ponctuelsThe increasing demanded of components allowing operating in strong power in high frequency and in high temperatures drove to the development of electronics system on semiconductors base to wide band gap such as the gallium nitride (GaN) and silicon carbide (SiC). However the performances are limited by the quality of the material (impurities, crystallographic defects). In this thesis, we are interested in the study of two devices: MESFETs 4H-SiC, HEMTs AlGaN/GaN/Si for hyperfrequency and power applications. The study of the output characteristics revals anomalies. For MESFETsH-SiC, hysteresis effect on drain/source conductance spectacular Kink effect and shift of voltage has been observed. The DLTS and CDLTS measurements demonstrate that these effects are principally due to the presence of deep centers in the structures. For HEMT AlGaN/GaN/Si, hysteresis effect, series resistance is observed. The CDLTS measurements with impulses on the drain demonstrate the presence of punctual traps by extended defects.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceTunisiaFRT

Propriétés optiques et modélisation des structures à base de boîtes quantitques pour l'émission à 1,3 m

Dans ce travail, des structures à boîtes quantiques (BQs) InAs de faible densité émettant à 1,3 m sur substrat GaAs ont été réalisées par épitaxie par jets moléculaires. Les performances optoélectroniques des BQs ont été mesurées principalement par spectroscopie optique. L étude d une BQ unique par micro-photoluminescence a permis de mettre en évidence les raies d'émissions des excitons et biexcitons (antiliants) associés aux niveaux fondamentaux des boîtes. Certains spectres à raies multi-excitoniques enregistrés à très basse puissance d excitation ont été attribués à des configurations excitoniques sous l'effet du couplage latéral entre deux BQs. Ces observations expérimentales ont été confirmées théoriquement par la résolution de l'équation de Schrödinger à trois dimensions dans l'approche de la combinaison linéaire des orbitales atomiques pour construire les états moléculaires. Enfin, les propriétés optiques des BQs isolées et couplées latéralement en présence d un champ électrique ont été étudiées théoriquement, montrant l importance de l application d un champ électrique pour contrôler l état de charge dans une BQ unique et sur les différents états excitoniques dans une molécule de BQs pour les applications de traitement quantique de l'information.Low density of self-organized InAs/GaAs quantum dots (QDs) emitting at 1.3 m were grown by molecular beam epitaxy. The photoluminescence, its power and temperature dependences were studied for the ensembles of InAs QDs embedded in a GaAs matrix to investigate optical properties. Single InAs/GaAs QDs are studied using micro-photoluminescence spectroscopy. Single dot spectroscopy shows an antibinding biexciton. Some of these QDs are laterally coupled due to an anisotropic dot repartition. At low excitation power density, four exciton emissions are observed and are interpreted as the four possible exciton recombinations of two coupled QDs. Experimental results were confirmed theoretically by resolving the three dimensional Schrödinger equation in the approach of a linear combination of atomic molecular-orbital molecular. Finally, optical properties dependence on the magnitude of applied electrical field of single and coupled QDs was investigated, showing the importance of such electrical field to control charge in single dots and excitonic states in QDs molecules for quantum computation applications.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

DC and RF characteristics optimization of AlGaN/GaN/BGaN/GaN/Si HEMT for microwave-power and high temperature application

AlGaN/GaN/Si high electron mobility transistors (HEMTs) developed by molecular beam epitaxy (MBE) are studied with several methods for characterization, the most utilized are direct-current and radio-frequency measurements, to see power and microwave performance of components. The increase in these parameters is not based just with on improvement technological for example, decrease of length gate (Lg) and passivation. For sure, another very important point is to reduce the thickness of barrier while keeping the reduction in the length of gate, in order to reduce the transit time (τ), and consequently access to highest cut-off frequency (FT). For this situation, it’s appears a harmful phenomenon of type “punch-through”, because of the weak confinement of electrons in the channel. In this paper, the main objective is to show how to reduce this effect. Keywords: HEMT GaN, Current-voltage characteristics, RF characteristics, Alloys BGaN, Radio-frequenc

Structural and optical study of BInGaAs/GaAs quantum wells grown by MOVPE emitting above 1.1eV

International audienc