The optical response functions and band structures of LiCoO2 are studied at different levels of approximation, from density functional theory (DFT) in the generalized gradient approximation (GGA) to ...quasiparticle self-consistent QS G W (with G for Green's function and W for screened Coulomb interaction) without and with ladder diagrams ( QS G ˆ W ) and the Bethe Salpeter Equation (BSE) approach. The QS G W method is found to strongly overestimate the band gap and electron-hole or excitonic effects are found to be important. They lower the quasiparticle gap by only about 11% but the lowest energy peaks in absorption are found to be excitonic in nature. The contributions from different band to band transitions and the relation of excitons to band-to-band transitions are analyzed. The excitons are found to be strongly localized. A comparison to experimental data is presented.
The electronic band structures of BeSiN
and BeGeN
compounds are calculated using the quasiparticle self-consistent GW method. The lattice parameters are calculated for the wurtzite based crystal ...structure commonly found in other II-IV-N
compounds with the Pbn2
space group. They are determined both in the local density approximation and generalized gradient approximation, which provide lower and upper limits. At the GGA lattice constants, which gives lattice constants closer to the experimental ones, BeSiN
is found to have an indirect band gap of 6.88 eV and its direct gap at Formula: see text is 7.77 eV, while in BeGeN
the gap is direct at Formula: see text and equals 5.03 eV. To explain the indirect gap in BeSiN
comparisons are made with the parent III-N compound w-BN band structure. The effective mass parameters are also evaluated and found to decrease from BeSiN
to BeGeN
.
V2O5 with a layered van der Waals (vdW) structure has been widely studied because of the material’s potential in applications such as battery electrodes. In this work, microelectronic devices were ...fabricated to study the electrical and optical properties of mechanically exfoliated multilayered V2O5 flakes. Raman spectroscopy was used to determine the crystal structure axes of the nanoflakes and revealed that the intensities of the Raman modes depend strongly on the relative orientation between the crystal axes and the polarization directions of incident/scattered light. Angular dependence of four-probe resistance measured in the van der Pauw (vdP) configuration revealed an in-plane anisotropic resistance ratio of ∼100 between the a and b crystal axes, the largest in-plane transport anisotropy effect experimentally reported for two-dimensional (2D) materials to date. This very large resistance anisotropic ratio is explained by the nonuniform current flow in the vdP measurement and an intrinsic mobility anisotropy ratio of 10 between the a and b crystal axes. Room-temperature electron Hall mobility up to 7 cm2/(V s) along the high-mobility direction was obtained. This work demonstrates V2O5 as a layered 2D vdW oxide material with strongly anisotropic optical and electronic properties for novel applications.
Lu
et al.
(2022),
24
, 5529 uses incorrect explanations for their findings based on an incorrect application of ideas from tight-binding methods. An alternative qualitative explanation based on ...strain variations and a tight-binding model based on nearest neighbor interactions is provided.
The paper commented on addresses the crystal field splitting in AlGaN. Here, an alternative model based on bond-angle effects is proposed.
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