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We study the growth and properties of the quaternary-alloy ferromagnetic semiconductor (In0.94−x,Gax,Fe0.06)Sb (x = 5%–30%; the Fe concentration is fixed at 6%) grown by low-temperature molecular beam epitaxy. Reflection high-energy electron diffraction patterns, scanning transmission electron microscopy lattice images, and x-ray diffraction spectra indicate that the (In0.94−x,Gax,Fe0.06)Sb layers have a zinc blende crystal structure without any other second phase. The lattice constant of the (In0.94−x,Gax,Fe0.06)Sb films changes linearly with the Ga concentration x, indicating that Ga atoms substitute In atoms in the zinc-blende structure. We found that the carrier type of (In0.94−x,Gax,Fe0.06)Sb can be systematically controlled by varying x, being n-type when x ≤ 10% and p-type when x ≥ 20%. Characterization studies using magnetic circular dichroism spectroscopy indicate that the (In0.94−x,Gax,Fe0.06)Sb layers have intrinsic ferromagnetism with relatively high Curie temperatures (TC = 40–120 K). The ability to widely control the fundamental material properties (lattice constant, bandgap, carrier type, and magnetic property) of (In0.94−x,Gax,Fe0.06)Sb demonstrated in this work is essential for spintronic device applications. [ABSTRACT FROM AUTHOR]

We demonstrate spin-valve magnetoresistance (MR) with a current-in-plane (CIP) configuration in (Ga,Fe)Sb/InAs (thickness tInAs nm)/(Ga,Fe)Sb trilayer heterostructures, where (Ga,Fe)Sb is a ferromagnetic semiconductor (FMS) with high Curie temperature (TC). An MR curve with an open minor loop is clearly observed at 3.7 K in a sample with tInAs = 3 nm, which originates from the parallel-antiparallel magnetization switching of the (Ga,Fe)Sb layers and spin-dependent scattering at the (Ga,Fe)Sb/InAs interfaces. The MR ratio increases (from 0.03 to 1.6%) with decreasing tInAs (from 9 to 3 nm) due to the enhancement of the interface scattering. This demonstration of the spin-valve effect in Fe-doped FMS heterostructures paves the way for device applications of the high-TC FMS. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) systems, such as high-temperature superconductors, surface states of topological insulators, and layered materials, have been intensively studied using vacuum-ultraviolet (VUV) angle-resolved photoemission spectroscopy (ARPES). In semiconductor films (heterostructures), quantum well (QW) states arise due to electron/hole accumulations at the surface (interface). The quantized states due to quantum confinement can be observed by VUV-ARPES, while the periodic intensity modulations along the surface normal (k z) direction of these quantized states are also observable by varying incident photon energy, resembling three-dimensional (3D) band dispersion. We have conducted soft X-ray (SX) ARPES measurements on thick and ultrathin III-V semiconductor InSb(001) films to investigate the electronic dimensionality reduction in semiconductor QWs. In addition to the dissipation of the k z dispersion, the SX-ARPES observations demonstrate the changes of the symmetry and periodicity of the Brillouin zone in the ultrathin film as 2D QW compared with these of the 3D bulk one, indicating the electronic dimensionality reduction of the 3D bulk band dispersion caused by the quantum confinement. The results provide a critical diagnosis using SX-ARPES for the dimensionality reduction in semiconductor QW structures. • The electronic structures of the thick and ultrathin InSb films are observed by SX-ARPES. • The SX-ARPES observations demonstrate the changes in the symmetry and periodicity of the Brillouin zone. • SX-ARPES provides a critical diagnosis for the dimensionality reduction in semiconductor quantum well structures. [ABSTRACT FROM AUTHOR]

This paper proposes a numerical approximation method for analyzing the steady state and the transient state of sineware oscillator circuits. Since most oscillator circuits contain active and nonlinear elements (e.g., transistors), and inductive capacitive and by-pass components, their circuit equations generally become high-order nonlinear differential equations. The proposed method uses the Newton method to determine the operating point. The variation (ac component) about the operating point is used a variable for establishing a nonlinear differential equation to be solved by means of the Krylov-Bogolyubov-Mitropolsky asymptotic method. The discrete Fourier transform is then applied repeatedly to obtain the second-order approximation for the periodic solutions. The approximation method for transient solutions is also discussed. Finally, an example of a transistorized CR phase-shift oscillator is used to demonstrate the usefulness of the proposed method. The periodic and transient solutions obtained by the proposed method are compared to those of the Runge-Kutta-Gill method. [ABSTRACT FROM AUTHOR]