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The frequency dispersion in admittance measurements in AlGaN/GaN high-electron-mobility transistors, which is typically interpreted to result from an interface trap density Dit, is also known to be caused by effects other than Dit. To study the origin of two peaks of conductance component "Gp/ω" as a function of frequency in lateral gated diodes using AlGaN/GaN structures on Si wafers grown by metal–organic chemical vapor deposition, we measured capacitance C and conductance Gp/ω–voltage V as a function of angular frequency ω (C–ω–V and Gp/ω–ω–V, respectively) of long-gate field-effect transistors with a varied gate length. We also simulated the C–ω–V and Gp/ω–ω–V curves using an equivalent circuit that consisted of actually measured component parameters without Dit. We confirmed that the Gp/ω–ω curves show two peaks caused by the two-dimensional electron gas channel resistance and the gate current leakage and quantitatively determined the two ωpeak positions and intensities. We also discussed the effect of acceptor concentration in the GaN channel-layer on lowering of ωpeak at weak inversion. [ABSTRACT FROM AUTHOR]

The influence of the electrical conductivity of a Permalloy waveguide on the spin wave propagation was investigated using the finite-element solution of the combined system of quasistatic electromagnetic potential and linearized LLG (Landau–Lifshitz–Gilbert) equations. The difference in the group velocity between the conductive and nonconductive waveguides becomes large for films over 300 nm thick, and the difference is very small for film thicknesses less than 100 nm. The observed enhancement of the group velocity with increasing film thickness is attributed to the damping caused by the electrical conductivity, which leads to narrowing of the spin wave packet envelope and shorter arrival times of propagating waves. The basic characteristics of the dispersion relations do not change between conductive and nonconductive films for small film thicknesses less than 300 nm. The simulated dispersion relations indicate shift of their maximum intensity toward lower wavenumbers and, therefore, increase in the group velocity with increasing thickness. The simulated decay length of the spin waves for conductive films initially increases but then decreases with increasing thickness, which agrees well with the experimental results. The extracted damping coefficients from both simulations and the experiment agree very well and increase proportionally with d2, where d is the film thickness, due to the additional eddy current damping. The observed thickness and conductivity dependence of spin wave propagation is crucial for magnonics research and toward the development of future spin wave devices using metal films. [ABSTRACT FROM AUTHOR]

The dependence of nonreciprocity of excitation of magnetostatic surface waves on antenna width was investigated experimentally and theoretically. The nonreciprocity was successfully modified by changing the excitation antenna width. The nonreciprocity ratio, which was defined as the spin wave intensity under negative bias field divided by that under positive bias field, was found to decrease with increasing antenna width. Micromagnetic simulations revealed that this decrease in the nonreciprocity ratio originates from the rapid decrease in the in-plane excitation field compared to the perpendicular excitation field with reducing the antenna width. [ABSTRACT FROM AUTHOR]

Spin wave propagation in a magnonic crystal excited at a specific wavenumber was investigated by micromagnetic simulation modelling with meander-shaped antennae. The dispersion relation when excited at wave number k which corresponds to the boundary of the Brillouin zone, shows a pair of strong spots that originate from the magnonic upper and lower bands. When excited at wavenumber slightly offset from k above, additional strong spots appear and it shows intensity nonreciprocity reversal. It can be interpreted in terms of the repeated or reduced zone scheme of the Brillouin zone. These characteristics have the potential for novel control of nonreciprocity. [ABSTRACT FROM AUTHOR]

Epitaxial yttrium-iron garnet (YIG) films with various thicknesses were fabricated on gadolinium-gallium garnet substrates by a metal–organic decomposition (MOD) method, and their dynamic and static magnetic properties were investigated. We varied the thickness of the YIG films by repeating spin-coating of the MOD solution and pre-annealing. The lattice constant and the crystal size of the YIG films were almost independent of the thickness (the coating count N). The damping factor and coercive field increased with N. Moreover, the saturation magnetization MS measured using a vibrating sample magnetometer increased with N, although that measured by ferromagnetic resonance was almost independent of N. Thus, both dynamic and static magnetic properties for the YIG films obviously degraded with increasing N. Judging from these results, the repetition of the coating process generates other ferromagnetic micro-crystalline phases at grain boundaries, for instance, γ-Fe2O3 and Fe3O4, which could cause degradation of the magnetic properties of the YIG films prepared by the MOD method. [ABSTRACT FROM AUTHOR]

The width dependence of propagation properties for magnetostatic surface spin waves (MSSWs) in Permalloy (Py) waveguides was investigated experimentally and numerically. When both the short-side width of a Py waveguide (WPy) and the magnetic field (μ0H) were large enough, the spin wave (SW) intensity almost linearly decreased with decreasing WPy, and the resonant frequency fr was almost independent of WPy. However, when both WPy and μ0H were small, the SW intensity rapidly reduced, and fr decreased with decreasing WPy. Micromagnetic simulations revealed that when both WPy and μ0H are large enough, the magnetization direction of Py is almost parallel to the magnetic field direction, and the SW mode becomes the MSSW mode. In contrast, when both WPy and μ0H are small, magnetization direction tilts to the long-side direction of the Py strip from the magnetic field direction due to a strong demagnetizing field, which is the origin of the unexpected reduction in the intensity and fr. When miniaturized ferromagnetic waveguides are used for shrinking MSSW devices, a sufficiently large magnetic field is necessary because the influence of the shape magnetic anisotropy cannot be ignored. [ABSTRACT FROM AUTHOR]

The band diagrams of InAsxSb1−x/AlyIn1−ySb quantum wells (QWs) were calculated covering a wide range of compositions of x and y. Various combinations of active (InAsxSb1−x) and barrier (AlyIn1−ySb) layers were investigated to optimize the Hall elements with high sensitivity and high thermal stability. For high sensitivity, x of 0.1–0.6 is desirable due to the band bowing effect to realize lower bandgaps compared with that of InSb in the active layer. Under the lattice matched conditions (y ∼ 1.22x), the QWs are type II QWs and the bottom of the conduction band is always lower than the Fermi level. Therefore, the QWs with x of 0.6 show large sheet carriers of 4.1 × 1011 cm−2 for 4.2 K without intentional doping, which contributes to the reduction in the temperature dependence of the transport properties. The barrier height monotonously increases with increasing y, and accordingly, the penetration depth of the wave function probability inside the barrier decreases. Under the lattice matched condition, the penetration depth drops significantly toward x = 0.4 (corresponding y ∼ 0.5) and then decreases slowly. Thus, x ≥ 0.4 (y ≥ 0.5) is preferable for a strong confinement effect, which could reduce interface scattering and, as a result, improve the electron mobility. Judging from these results, the optimized composition of the InAsxSb1−x/AlyIn1−ySb QW is x = 0.4–0.6 (under the lattice matched condition, corresponding y = 0.5–0.7). [ABSTRACT FROM AUTHOR]

Mass production-ready technologies of AlGaN/AlN/GaN high-electron-mobility transistor (HEMT) structures on 200 mm diameter silicon substrates are developed using a large-scale metal-organic chemical vapor deposition system. High-yield epitaxial substrates on large-diameter wafers are required for reducing the cost of industrializing power device applications. Through multi-point vertical leakage current measurements, it was confirmed that the AlGaN/AlN/GaN HEMT, under optimum growth conditions, showed high yield characteristics such as a highly uniform leakage current and a low number of breaking points over the entire 200 mm diameter wafer. On introducing an AlN spacer layer between the AlGaN Schottky barrier and the GaN channel, a lower on-state resistance for power devices can be expected. Cross-sectional transmission electron microscopy images revealed that the thin AlN spacer layer was grown between the AlGaN and GaN layers with atomically abrupt and flat interfaces. HEMT structures with an AlN spacer layer exhibited a considerably high two-dimensional-electron-gas mobility of 2000 cm2 V−1 s−1 at room temperature and 10 700 cm2 V−1 s−1 at 77 K. The AlN spacer layer between the AlGaN and GaN layers was successfully fabricated and suppressed the alloy disorder scattering effect. [ABSTRACT FROM AUTHOR]

We investigated the magneto-optical properties of submicron-size epitaxial Bi-substituted yttrium-iron garnet (Bi:YIG) patterns fabricated by an electron-beam irradiated metal-organic decomposition (EB-MOD) method. The advantage of this method is that no dry etching process is required. The Bi:YIG pattern showed the clear magneto-optical Kerr effect (MOKE) hysteresis loop, and it was in good agreement with the magnetization curve of the Bi:YIG patterns. The MOKE image measurements revealed that the Bi:YIG pattern with a width of ∼0.71 μm prepared by the EB-MOD showed proper contrast changing behavior depending on magnetic fields, and it can maintain its MO property even in submicron-size. [ABSTRACT FROM AUTHOR]

We examine electrical properties of pseudo-single-crystalline (PSC) Ge films, formed by modulated Au-induced-crystallization (GIC) method, on glass substrates. Although higher growth temperatures and thicker Au layers in GIC conditions degrade the Hall mobility of holes, the influence of the Au deep centers can be ignored. For the thin film transistors, we find that post annealing in N 2 atmosphere enables us to enhance field-effect mobility and the on-off ratios. We discuss the mechanism of the improvement of electrical properties of the PSC-Ge films on the glass substrate. [ABSTRACT FROM AUTHOR]

We show nonlocal spin transport in n-Ge-based lateral spin-valve devices with highly ordered Co2FeSi/n+-Ge Schottky tunnel contacts. Clear spin-valve signals and Hanle effect curves are demonstrated at low temperatures, indicating the generation, manipulation, and detection of pure spin currents in n-Ge. The obtained spin generation efficiency of ∼0.12 is about two orders of magnitude larger than that for a previously reported device with Fe/MgO tunnel barrier contacts. Considering the spin-related behavior with temperature evolution, we infer that it is necessary to simultaneously demonstrate a high spin generation efficiency and improve the quality of the transport channel to realize Ge-based spintronic devices. [ABSTRACT FROM AUTHOR]

We perform a detailed comparison of the nonlocal magnetoresistance (MR) curve with the local MR ones in Si-based lateral spin-valve devices with epitaxial ferromagnetic Fe3Si contacts, where the local MR originates from the anisotropic MR of the ferromagnetic contacts. We find that the nonlocal MR signals clearly depend on the magnetization reversal of the contacts, and they show positive or negative peak values when the magnetic configuration between two ferromagnetic contacts becomes nearly anti-parallel. These features mean that the obtained nonlocal MR signals can be distinguished from the suspicious signals, indicating a reliable result of the spin transport in Si. [ABSTRACT FROM AUTHOR]

Antireflection nanostructures for GaN light-emitting diodes (LEDs) were fabricated by reactive ion etching (RIE) using Ni as an etching mask. The Ni mask was formed by electrodeposition in combination with ultraviolet nanoimprint lithography (UV-NIL). The antireflection nanostructures of 600 nm in depth, 300 nm in diameter, and 500 nm in pitch were fabricated on a GaN substrate. The radiant intensity of the LEDs was increased 1.5 times compared to that of a conventional LED. Since this method enables the fabrication of wafer-level GaN nanostructures with a low cost process, it is applicable to the fabrication of photonic crystals. [ABSTRACT FROM AUTHOR]

Abstract: We have explored an effect of the interface resistance of Fe3Si/n +-Ge Schottky-tunnel contacts on spin accumulation created electrically in n-Ge. Using the Schottky-tunnel contacts with a relatively high interface resistance, we can clearly detect spin-accumulation signals in n-Ge even at room temperature, meaning that the use of highly resistive Schottky tunnel contacts is effective to electrically create large spin accumulation. Since such highly resistive source and drain electrodes are not available for next-generation Ge-based spintronic applications with ultra-low power consumption, the development of highly spin-polarized spin injectors such as half-metallic materials is essential from now on. [Copyright &y& Elsevier]