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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]

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]