Search results for " Ga"
showing 10 items of 12404 documents
Bandgap behavior and singularity of the domain-induced light scattering through the pressure-induced ferroelectric transition in relaxor ferroelectri…
2018
[EN] In this letter, we have investigated the electronic structure of A(x)Ba(1-x)Nb(2)O(6) relaxor ferroelectrics on the basis of optical absorption spectroscopy in unpoled single crystals with A = Sr and Ca under high pressure. The direct character of the fundamental transition could be established by fitting Urbach's rule to the photon energy dependence of the absorption edge yielding bandgaps of 3.44(1) eV and 3.57(1) eV for A = Sr and Ca, respectively. The light scattering by ferroelectric domains in the pre-edge spectral range has been studied as a function of composition and pressure. After confirming with x-ray diffraction the occurrence of the previously observed ferroelectric to pa…
Photo-electrical and transport properties of hydrothermal ZnO
2016
We performed the studies of optical, photoelectric, and transport properties of a hydrothermal bulk n-type ZnO crystal by using the contactless optical techniques: photoluminescence, light-induced transient grating, and differential reflectivity. Optical studies revealed bound exciton and defect-related transitions between the donor states (at ∼60 meV and ∼240 meV below the conduction band) and the deep acceptor states (at 0.52 eV above the valence band). The acceptor state was ascribed to VZn, and its thermal activation energy of 0.43 eV was determined. A low value of carrier diffusion coefficient (∼0.1 cm2/s) at low excitations and temperatures up to 800 K was attributed to impact the rec…
Enabling partially reconfigurable IP cores parameterisation and integration using MARTE and IP-XACT
2012
International audience; This paper presents a framework which facilitates the parameterization and integration of IP cores into partially reconfigurable SoC platforms, departing from a high-level of abstraction. The approach is based in a Model-Driven Engineering (MDE) methodology, which exploits two widely used standards for Systems-on-Chip specification, MARTE and IP-XACT. The presented work deals with the deployment level of the MDE approach, in which the abstract components of the platform are first linked to the lower level IP-XACT counterparts. At this phase, information for parameterization and integration is readily available, and a synthesizable model can be obtained from the gener…
A fully-digital realtime SoC FPGA based phase noise analyzer with cross-correlation
2017
We report on a fully-digital and realtime operation of a phase noise analyzer using modern digital techniques with cross-correlation. With the advent of system on chip field-programmable gate arrays (SoC FPGAs) embedding hard core central processing unit, coprocessor and FPGA onto a single integrated circuit, the building of sensitive analysis devices for Time & Frequency research is made accessible at virtually no cost and benefits from reconfigurability. Used with high-speed digitizers we have successfully implemented a four-channel system whose preliminary results at 10 MHz shows a residual white noise floor < −185 dBrad2/Hz up to 5 MHz off the carrier, and flicker < −127 dBrad2/Hz using…
Pressure-induced insulator-to-metal transition in α-SnWO4
2016
In-situ high-pressure W L1 and L3 edges x-ray absorption and mid-infrared spectroscopies complemented by first-principles calculations suggest the existence of pressure- induced insulator-to-metal transition in α-SnWO4 in the range of 5-7 GPa. Its origin is explained by a symmetrization of metal-oxygen octahedra due to a strong interaction of Sn 5s, W 5d and O 2p states along the b-axis direction, leading to a collapse of the band gap.
Parasitic Bipolar Action in SiC Power MOSFETs Demonstrated by Two-Photon Laser Experiment
2018
A two-photon absorption technique is explored for Silicon carbide power MOSFETs and power junction barrier Schottky diodes using a pulsed laser. The similarities in design between the specific MOSFETs and diodes tested permit using mechanisms existing in the different structures as explanation for observed current variation with laser position. The diode shows variation in average current with change in laser depth only, whereas the MOSFET shows variation both with shifts in depth and shifts in position across the striped geometry of the device. The variation is explained to be due to bipolar amplification of the charge carriers generated in the MOSFET when a pulse focus includes a channel …
The effects of thermal treatment on structural, morphological and optical properties of electrochemically deposited Bi2S3 thin films
2017
Abstract Thin films of bismuth sulfide (Bi 2 S 3 ) have been electrochemically deposited on indium–doped tin oxide substrates from aqueous solutions of Bi(NO 3 ) 3 , ethylene diamine tetraacetic acid (EDTA) and Na 2 S 2 O 3 . The structural properties of the films were characterized using X–ray diffraction and high–resolution transmission electron microscopy analyses. The film crystallizes in an orthorhombic structure of Bi 2 S 3 along with metallic bismuth. Thermal annealing of the prepared film in sulfur atmosphere improves its crystallinity and cohesion. The band gap values of the deposited film before and after annealing at 400 °C were found to be 1.28 and 1.33 eV, respectively.
Multiple low-frequency broad band gaps generated by a phononic crystal of periodic circular cavity sandwich plates
2017
Abstract We propose a new type of phononic crystal (PnC) composed of a periodic alternation of circular cavity sandwich plates. In the low-frequency regime, the crystal can modulate the propagation of flexural waves. Governing equations are deduced basing on the classical theory of coupled extensional and flexural vibrations of plates. The dispersion relation of the infinite PnC is calculated by combining the transfer matrix method with Bloch theory. The dynamic response of the PnC with finite unit cells is further studied with finite element analysis. An experiment is carried out to demonstrate the performance of the PnC in vibration isolation. Numerical results and experimental results bo…
Ultra-Wide Band Gap in Two-Dimensional Phononic Crystal with Combined Convex and Concave Holes
2017
A phononic crystal with an ultra‐wide band gap is proposed, whose unit cell consists of a cross‐like concave hole in the center and four square convex holes at the corners. The dispersion relations, modal kinetic energy ratio, and eigenmodes at edges of the band gaps are investigated by using the finite element method. The influence of the geometrical parameters of the convex and concave holes on the band gaps is further analyzed. After optimization, an ultra‐wide band gap with gap‐to‐midgap ratio of 156.0% is achieved, with the filling fraction keeping a relative small value. Numerical results illustrate that the combination of convex and concave holes is a practicable direction for struct…
Barrier inhomogeneity in vertical Schottky diodes on free standing gallium nitride
2019
Abstract In this paper, the electrical behavior of a Ni/Au Schottky barrier on free standing GaN has been studied employing a variety of techniques and correlated with the material and interface quality. The temperature dependence of the ideality factor (n) and of the Schottky barrier height (ΦB) revealed a spatial inhomogeneity of the barrier. This behavior has been described by means of the Tung's model on inhomogeneous Schottky barriers. The origin of the barrier inhomogeneity can be likely associated to the surface quality of the GaN epilayer or to microstructure of the Ni/GaN interface.