Defect control and Si/Ge core-shell heterojunction formation on silicon nanowire surfaces formed using the top-down method

Control of surface defects and impurity doping are important keys to realizing devices that use semiconductor nanowires (NWs). As a structure capable of suppressing impurity scattering, p-Si/i (intrinsic)-Ge core-shell NWs with radial heterojunctions inside the NWs were formed. When forming NWs using a top-down method, the positions of the NWs can be controlled, but their surface is damaged. When heat treatment for repairing surface damage is performed, the surface roughness of the NWs closely depends on the kind of atmospheric gas. Oxidation and chemical etching prior to shell formation removes the surface damaged layer on p-SiNWs and simultaneously achieves a reduction in the diameter of the NWs. Finally, hole gas accumulation, which is important for suppressing impurity scattering, can be observed in the i-Ge layers of p-Si/i-Ge core-shell NWs.

Study on spin current transmission of Co1-x Tb x films

We investigate the spin to charge conversion phenomena in Y3Fe5O12/Pt/Co1-x Tb x /Pt multilayers by both the spin pumping and spin Seebeck effects. We find that the spin transport efficiency is irrelevant to magnetization states of the perpendicular magnetized Co1-x Tb x films, which can be attributed to the symmetry requirement of the inverse transverse spin Hall effect. Furthermore, the spin transmission efficiency is significantly affected by the film concentration, revealing the dominant role of extrinsic impurity scattering caused by Tb impurity. The present results provide further guidance for enhancing the spin transport efficiency and developing spintronics devices.

Interaction of an electromagnetic E-wave with a thin conducting film between two dielectric media in the case of an anisotropic isoenergetic surface and impurity scattering

The coefficients of reflection, transmission and absorption are calculated in the framework of the kinetic approach, when an electromagnetic E-wave interacts with a thin conducting film located between two dielectric media. To account for the surface scattering of charge carriers is used a model of mirror-diffuse boundary conditions, assuming that the specularity coefficients of the upper and lower surfaces of the film differ from each other. The electromagnetic wave falls on the upper surface of the film at an arbitrary angle. The case of an anisotropic isoenergetic surface of a conductor having the form of a three-axis ellipsoid, one of the main axes of which is parallel to the magnetic field strength of the wave, and the other is perpendicular to the film surfaces, is considered. The impurity scattering of electrons (holes) is dominated in the volume of the conductor. The dependence of the absorption coefficient on the parameters of the isoenergetic surface of the conductor is analyzed.

Influence of Impurity Scattering on Surface Plasmons in Graphene in the Lindhard Approximation

We study the influence of impurity scattering on transverse magnetic (TM) and transverse electric (TE) surface plasmons (SPs) in graphene using the Lindhard approximation. We show how the behaviour and domains of TM SPs are affected by the impurity strength γ and determine the critical value γc below which no SPs exist. The quality factor of TM SPs, for single-band and two-band transitions, is proportional to the square of αλSP/γ, with α being the fine-structure constant and λSP being the plasmon wavelength. In addition, we show that impurity scattering suppresses TE SPs.

Conductivity Mechanism of Ion–DNA Interaction in Dilute Solution

In this paper, we propose an impurity scattering model of quasi-one-dimensional disordered system for ion–DNA interaction in dilute solution based on the density of state in non-periodic DNA. This disordered system is composed of cations and DNA, the hydrogen ions adsorbed on the surface of DNA with negative charges are considered as impurities. It is hydrogen ions in hydration layer that cause the variations of the density of state near the Fermi level. The classical theory describes the linear dependence of conductivity on concentration. By developing the Green function approach of ion–DNA interaction in the dilute solution, the quantum theory not only gives the linear part but also demonstrates the nonlinear part of the conductivity.

Improvement of p-Type AlGaN Conductivity with an Alternating Mg-Doped/Un-Doped AlGaN Layer Structure

Using molecular beam epitaxy, we prepared seven p-type AlGaN samples of ~25% in Al content, including six samples with Mg-doped/un-doped AlGaN alternating-layer structures of different layer-thickness combinations, for comparing their p-type performances. Lower sheet resistance and higher effective hole mobility are obtained in a layer-structured sample, when compared with the reference sample of uniform Mg doping. The improved p-type performance in a layer-structured sample is attributed to the diffusion of holes generated in an Mg-doped layer into the neighboring un-doped layers, in which hole mobility is significantly higher because of weak ionized impurity scattering. Among the layer-structured samples, that of 6/4 nm in Mg-doped/un-doped thickness results in the lowest sheet resistance (the highest effective hole mobility), which is 4.83 times lower (4.57 times higher) when compared with the sample of uniform doping. The effects of the Mg-doped/un-doped layer structure on p-type performance in AlGaN and GaN are compared.

Comparison of THz-QCL Designs Supporting Clean N-Level Systems

Three different Terahertz quantum-cascade-laser designs supporting clean n-level systems were analyzed using nonequilibrium Green’s functions. In clean n-level systems, most of the electrons occupy the active laser levels, with thermally activated leakage channels being suppressed almost entirely up to room temperature. Simulations of the three designs, namely a resonant phonon design, a two-well design, and a split-well direct-phonon design were investigated. The results from the simulations indicated that the two-well design would perform best overall, in terms of variations in current density, interface roughness, and ionized impurity scattering. We conclude that future research aiming to improve the temperature performance of such laser designs should be based on a two-well design.