Search results for "resistivity"

Low-temperature growth of n ++-GaN by metalorganic chemical vapor deposition to achieve low-resistivity tunnel junctions on blue light emitting diodes

2018

We report on low-resistivity GaN tunnel junctions (TJ) on blue light-emitting diodes (LEDs). Si-doped n ++-GaN layers are grown by metalorganic chemical vapor deposition directly on LED epiwafers. Low growth temperature (<800 °C) was used to hinder Mg-passivation by hydrogen in the p ++-GaN top surface. This allows achieving low-resistivity TJs without the need for post-growth Mg activation. TJs are further improved by inserting a 5 nm thick In0.15Ga0.85N interlayer (IL) within the GaN TJ thanks to piezoelectric polarization induced band bending. Eventually, the impact of InGaN IL on the internal quantum efficiency of blue LEDs is discussed.

The ultrafast dynamics and conductivity of photoexcited graphene at different Fermi energies

2017

The ultrafast dynamics and conductivity of photoexcited graphene can be explained using solely electronic effects.

On the Phase Separation in n-Type Thermoelectric Half-Heusler Materials

2018

Half-Heusler compounds have been in focus as potential materials for thermoelectric energy conversion in the mid-temperature range, e.g., as in automotive or industrial waste heat recovery, for more than ten years now. Because of their mechanical and thermal stability, these compounds are advantageous for common thermoelectric materials such as Bi 2 Te 3 , SiGe, clathrates or filled skutterudites. A further advantage lies in the tunability of Heusler compounds, allowing one to avoid expensive and toxic elements. Half-Heusler compounds usually exhibit a high electrical conductivity σ , resulting in high power factors. The main drawback of half-Heusler compounds is their high lattice th…

Impedance characterization of the electrochemical environment under a polymer film artificially delaminated

2008

International audience; Knowledge of the electrical conductivity of the zone under a delaminated paint film is one necessary input parameter for the simulation of electrochemically driven underpaint corrosion. In this work, a microelectrode array system has been developed, tested, and applied to measure the spatial distribution of resistivity in the delaminated zone along the metal/polymer interface. The experimental device consists of a linear array of six 100 m diameter stainless steel microelectrodes (100 m in diameter) embedded in a steel substrate. A polymer coatingwas applied and an artificial "delaminated zone"was created using the laser-induced decohesion technique. The electrochemi…

Light absorption and electrical transport in Si:O alloys for photovoltaics

2010

Thin films (100-500 nm) of the Si:O alloy have been systematically characterized in the optical absorption and electrical transport behavior, by varying the Si content from 43 up to 100 at. %. Magnetron sputtering or plasma enhanced chemical vapor deposition have been used for the Si:O alloy deposition, followed by annealing up to 1250 °C. Boron implantation (30 keV, 3-30× 1014 B/cm2) on selected samples was performed to vary the electrical sheet resistance measured by the four-point collinear probe method. Transmittance and reflectance spectra have been extracted and combined to estimate the absorption spectra and the optical band gap, by means of the Tauc analysis. Raman spectroscopy was …

Exchange bias in epitaxial Mn2Au (0 0 1)/Fe (0 0 1) bilayers

2019

Epitaxial Mn2Au thin films for antiferromagnetic spintronics

2015

Mn2Au is one of the few candidate materials for antiferromagnetic spintronics requiring ordered metals with a high Neel-temperature and strong spin–orbit coupling. We report the preparation of epitaxial Mn2Au thin films by rf-sputtering. Structural characterization by x-ray and electron diffraction demonstrates a high degree of atomic order and the temperature dependence of the resistivity is typical for a good metal. The magnetic properties of the samples are studied by the investigation of Mn2Au/Fe bilayers. Exchange bias effects are observed, which present strong evidence for antiferromagnetic order in the Mn2Au thin films. Small domains of 500 nm are visualized in the exchange coupled F…

Conductimetry and impedance spectroscopy study of low pressure metal organic chemical vapor deposition TiN O films as a function of the growth temper…

2001

Abstract Titanium oxinitride thin films have been grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) using titanium isopropoxide, Ti(OCH(CH 3 ) 2 ) 4 (TIP) and NH 3 precursors in a growth temperature range from 450 to 750°C on sapphire substrates. The electrical behaviour of these films was studied between 400 and 173 K, revealing three different behaviours, ranking from a hopping conductivity (450–500°C) to a conducting one (700–750°C), with a dual behaviour for the intermediate growth temperatures. Moreover, at room temperature, both conductimetry and impedance spectroscopy highlighted a percolation behaviour, interpreted in terms of continuum percolation. The effect…

(La0.8Sr0.2)(Mn1−yFey)O3±δ oxides for ITSOFC cathode materials?

2005

The oxygen transport properties in (La 0.8 Sr 0.2 )(Mn 1-y Fe y )O 3±δ (LSMF) with various iron contents y = 0, 0.2, 0.5, 0.8 and 1 were determined by the IEDP technique. Both oxygen diffusion and surface exchange coefficients were found to be greater for y = 0.8 and 1 than those of LSM (y=0). Moreover, for y ≤0.5, grain boundary diffusion was the rate limiting step especially at lower temperatures. Thus, in the LSMF perovskite materials, the oxygen diffusion via oxygen vacancies is enhanced by Fe. The LSMF electrical performances were measured by impedance spectroscopy. Compared to LSM and LSF (y= 1), porous LSMF cathodes with y= 0.2-0.8 exhibit poor electronic conductivity: Fe, by reducin…

Electrical Transport in Lead-Free [(1−x)(Na0.5Bi0.5)-xBa]Zr1 - yTiyO3Ceramics (x = 0, 0.06, and y = 0, 0.96)

2009

Lead-free ceramics based on (Na 0.5 Bi 0.5 TiO 3 , NBT)-(Ba(Ti,Zr)O 3 , BTZ) were prepared by solid phase hot pressing sintering process and their ac (σ ac ) and dc (σ dc ) conductivity have been studied (303–753 K). Low frequency (100 Hz–100 kHz) ac conductivity obeys power law σ ac ∼ ω s characteristic for disordered materials. The frequency exponent s is a decreasing function of temperature and tends to zero at high temperatures. Dc conductivity has thermally activated character and possesses four linear parts with four different activation energies and some discontinous changes. However, σ ac (T) possesses two linear parts with two different activation energies and more discontinuous ch…