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A theoretical study is presented of the effect of an in-plane magnetic exchange field on the band structure of centrosymmetric films of noble metals and topological insulators. Based on an ab initio relativistic k ⋅ p theory, a minimal effective model is developed that describes two coupled copies of a Rashba or Dirac electronic system residing at the opposite surfaces of the film. The coupling leads to a structural gap at $\bar{{\Gamma}}$ and causes an exotic redistribution of the spin density in the film when the exchange field is introduced. We apply the model to a nineteen-layer Au(111) film and to a five-quintuple-layer Sb _2 Te _3 film. We demonstrate that at each film surface the exchange field induces spectrum distortions similar to those known for Rashba or Dirac surface states with an important difference due to the coupling: at some energies, one branch of the state loses its counterpart with the oppositely directed group velocity. This suggests that a large-angle electron scattering between the film surfaces through the interior of the film is dominant or even the only possible for such energies. The spin-density redistribution accompanying the loss of the counterpart favors this scattering channel.

Highlights: [•] GaNAsBi band structures have been calculated using BAC model and k ⋅ p method. [•] Band-gap energy of GaNAsBi lattice matched to GaAs decreases by 198meV/%Bi. [•] Spin–orbit splitting increases by 56meV/%Bi regardless N content. [•] A crossover at about 0.6eV has occurred between Eg and Δ so of GaN.039As.893Bi.068. [•] Effective masses behaviors of carriers have been discussed at Γ point. [Copyright &y& Elsevier]

A comparison of nanowire FETs (NWFETs) of identical geometries but operating in two different regimes, namely, the quantum capacitance (QC) and classical capacitance (CC) regimes, is presented, n-type InSb and InAs NWFETs up to ∼50 nm in diameter operate in the QC limit (QCL), and the corresponding p-type NWFETs operate in the CC limit. Drive currents at a fixed gate overdrive for the n- and p-type devices are found to be well matched. Nevertheless, the p-type devices have twice the delay times, half the intrinsic cutoff frequencies, twice the power-delay products, and four to five times the energy-delay products of the n-type devices, assuming transport is ballistic. Analytical expressions are derived for the QC, the current, the charge, the power-delay product, the energy-delay product, the gate delay time, and the cutoff frequency for a single-moded device operating in the QCL. The expressions for the power-delay product, energy-delay product, and the cutoff frequency are fundamental limits for such devices. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure and optical gain of InAsSbN/InAs QDs are investigated in the framework of effective-mass envelope function theory. The strain distribution is calculated using the valence force field (VFF) method. When the composition of Sb increases, both the conduction and valence bands offset and the compressive strain increase, and the transition energy decreases and the strained band alignment may change from type I to type II. The added nitrogen can reduce the compressive strain in QD, and it reduces the C1-HH1 transition energy due to the strong repulsion between nitrogen resonant band and conduction band. When the Sb composition increases, the overlapping of wave-functions of electrons and holes are less efficient, the optical transition matrix element decreases. For the optical gain, we should consider the factors including the transition matrix element, the matrix element of Kane’s theory, the refractive index and Fermi-Dirac distributions for electrons fc in the conduction bands and holes fv in the valence bands. So depending on the specific application requirements, we should select the appropriate compositions of Sb and N accordingly. [Copyright &y& Elsevier]