Effect of Multiple Quantum Well Periods on Structural Properties and Performance of Extended Short-Wavelength Infrared LEDs

We present research on the role of multiple quantum well periods in extended short-wavelength infrared InGaAs/InAsPSb type-I LEDs. The fabricated LEDs consisted of 6, 15, and 30 quantum well periods, and we evaluated the structural properties and device performance through a combination of theoretical simulations and experimental characterization. The strain and energy band offset was precisely controlled by carefully adjusting the composition of the InAsPSb quaternary material, achieving high valence and conduction band offsets of 350 meV and 94 meV, respectively. Our LEDs demonstrated a high degree of relaxation of 94-96 %. Additionally, we discovered that the temperature-dependent dark current characterization attributed to generation-recombination and trap-assign tunneling, with trap-assign tunneling being more dominant at lower current injections. Electroluminescence analysis revealed that the predominant emission mechanism of the LEDs originated from localized exciton and free exciton radiative recombination, which the 30 quantum wells LED exhibited the highest contribution of the localized exciton/free exciton radiative recombination. We observed that increasing the quantum well periods from 6 to 15 led to an increase in the 300 K electroluminescence intensity of the LED. However, extending the quantum well period to 30 resulted in a decline in emission intensity due to the degradation of the epitaxial film quality

Large positive in-plane magnetoresistance induced by localized states at nanodomain boundaries in graphene

Graphene supports long spin lifetimes and long diffusion lengths at room temperature, making it highly promising for spintronics. However, making graphene magnetic remains a principal challenge despite the many proposed solutions. Among these, graphene with zig-zag edges and ripples are the most promising candidates, as zig-zag edges are predicted to host spin-polarized electronic states, and spin-orbit coupling can be induced by ripples. Here we investigate the magnetoresistance of graphene grown on technologically relevant SiC/Si(001) wafers, where inherent nanodomain boundaries sandwich zig-zag structures between adjacent ripples of large curvature. Localized states at the nanodomain boundaries result in an unprecedented positive in-plane magnetoresistance with a strong temperature dependence. Our work may offer a tantalizing way to add the spin degree of freedom to graphene

Structure And Properties Of Rapidly Solidified And Mechanically Milled Nanostructured Al-Ni-Mm Alloys

The structure and mechanical properties of rapidly solidified Al-Ni-Mm (Mm: misch metal) alloys in the as-solidified or mechanically milled, and extruded conditions were investigated. The hardness of the Al86Ni 9Mm5 alloy varied with the solute content in the amorphous phase and the micro structure after heat treatment. The hardening in these nanocomposites was quantitatively explained using a rule-of-mixtures model based on the volume fraction of the phases. The effect of powder size on the microstructure and mechanical properties was studied in gasatomized powders and their extrudates. With decreasing powder size, formation of intermetallic compounds such as Al3Ni, Al11La3 and Al 11Ce3 was suppressed, and powders \u3c 26 urn in size consisted of nanocrystalline fcc-Al embedded in an amorphous matrix. Microstructural scale of the extruded bar decreased with decreasing initial powder size. The UTS of the alloy increased from about 512 to 728 MPa with decreasing initial powder size from 75-90 urn to \u3c 26 μm. To refine the microstructure and enhance the mechanical properties further, the coarse Al-Ni-Mm alloy powders were mechanically milled. Details of the microstructural development as a function of milling time and its effect on the microhardness of the alloy are discussed

Section-Dependent Microstructure And Mechanical Properties Of Rapidly Solidified And Extruded Al-20Si Alloy

The microstructure and mechanical properties of rapidly solidified and extruded Al-20Si alloys were studied by a combination of optical microscopy, scanning electron microscopy, X-ray diffraction, compression testing, and wear testing. The microstructure of the extruded bars showed a homogeneous distribution of different primary Si sizes and shapes embedded in the Al matrix depending on the section considered in the extruded bar. As the section changes from diagonal through perpendicular to parallel, the compressive yield strength increased from 219 through 225 to 263 MPa, respectively. The specific wear was the lowest at all sliding speeds for the parallel section in comparison to the perpendicular and diagonal sections of the extruded bar. © 2003 Elsevier Ltd. All rights reserved

Duffing oscillation-induced reversal of magnetic vortex core by a resonant perpendicular magnetic field.

Nonlinear dynamics of the magnetic vortex state in a circular nanodisk was studied under a perpendicular alternating magnetic field that excites the radial modes of the magnetic resonance. Here, we show that as the oscillating frequency is swept down from a frequency higher than the eigenfrequency, the amplitude of the radial mode is almost doubled to the amplitude at the fixed resonance frequency. This amplitude has a hysteresis vs. frequency sweeping direction. Our result showed that this phenomenon was due to a Duffing-type nonlinear resonance. Consequently, the amplitude enhancement reduced the vortex core-switching magnetic field to well below 10 mT. A theoretical model corresponding to the Duffing oscillator was developed from the Landau-Lifshitz-Gilbert equation to explore the physical origin of the simulation result. This work provides a new pathway for the switching of the magnetic vortex core polarity in future magnetic storage devices

Uncooled mid-wavelength InAsSb/AlAsSb heterojunction photodetectors

A mid-wavelength p–B–i–n infrared photodetector constituting ternary alloys of an InAs0.9Sb0.1 absorber and an AlAs0.05Sb0.95 electron barrier was demonstrated to operate at room temperature. The results of high-resolution x-ray diffraction (XRD) analysis indicate the high crystalline quality of the barriode detector structure, grown via molecular beam epitaxy, as supported by the strong XRD peak intensity of InAsSb and its corresponding defect density as low as ∼2.0 × 108 cm−2. The dark current of the barriode detector remained diffusion-limited in the 280–300 K temperature range, and generation–recombination became dominant at 220–260 K owing to the deep-level traps in the depletion region of the absorber and near the lattice-mismatched heterointerface of AlAsSb/InAsSb. Two distinct shallow traps in the InAsSb absorber were identified through Laplace deep-level transient spectroscopy with the activation energies of Et1 = 20 meV and Et2 = 46 meV. The Et1 trap is associated with the hole localization states induced by the alloy disorder of InAsSb, whereas the Et2 trap originated from a point defect of In vacancies in InAsSb. At 300 K, the barriode detector exhibited a 90% cutoff wavelength of 5.0 μm, a peak current responsivity of 0.02 A/W, and a dark current density of 1.9 × 10−3 A/cm2 under a bias voltage of −0.3 V, providing a high specific detectivity of 8.2 × 108 cm Hz1/2/W

Optimum Dopant Content Of N-Type 95% Bi2Te3 + 5% Bi2Se3 Compounds Fabricated By Gas Atomization And Extrusion Process

The n-type (Bi2Te3-Bi2Se3) compound was newly fabricated by gas atomization and hot extrusion, which is considered to be a mass production technique of this alloy. The aim of this research is to analyze the effect of the amount of dopant on the thermoelectric properties for n-type 95% Bi2Te3 + 5% Bi2Se3 compounds. The microstructure of extruded bar shows homogeneous and fine distribution of grains through full length due to dynamic recrystallizaiton during hot extrusion. The absolute values of Seebeck coefficient for the compounds doped 0.02, 0.04, 0.07 and 0.1 wt.% SbI3 are 219.9, 175, 147.7 and 146.7 μV/K, respectively. The electrical resistivity (ρ) is highest at 0.02 wt.% SbI3, while lowest is at 0.1 wt.% SbI3. The compound with 0.04 wt.% SbI3 shows the highest power factor among the four; different dopant contents because of the relative high Seebeck coefficient and the low electrical resistivity. © 2005 Elsevier B.V. All rights reserved

Positive exchange bias in thin film multilayers produced with nano-oxide layer

We report a positive exchange bias in thin film multilayers produced with nano-oxide layer. The positive exchange bias resulted from an antiferromagnetic interfacial exchange coupling between the ferromagnetic CoFe and the antiferromagnetic CoO layers, which spontaneously forms on top of the nano-oxide layer during the subsequent deposition of a CoFe layer. The shift in the hysteresis loop along the direction of the cooling field and the change in the sign of exchange bias are evidence of antiferromagnetic interfacial exchange coupling. The high temperature positive exchange bias observed for our system results from magnetic proximity effects between CoFe and CoO