Interband Transition Theory Research Articles

Optical absorption of bismuthene with a single vacancy: first-principle calculations.

The exceptional mechanical, electronic, topological, and optical properties, make bismuthene an ideal candidate for various applications in ultrafast saturation absorption and spintronics. Despite the extensive research efforts devoted to synthesizing this material, the introduction of defects, which can significantly affect its properties, remains a substantial obstacle. In this study, we investigate the transition dipole moment and joint density of states of bismuthene with/without single vacancy defect via energy band theory and interband transition theory. It is demonstrated that the existence of the single defect enhances the dipole transition and joint density of states at lower photon energies, ultimately resulting in an additional absorption peak in the absorption spectrum. Our results suggest that the manipulation of defects in bismuthene has enormous potential for improving the optoelectronic properties of this material.

Temperature-dependent dielectric functions of bcc transition metals Cr, Mo, and W from ultraviolet to infrared regions: A theoretical and experimental study

In the bcc transition metals Cr, Mo, and W, the existence of the partially filled d bands makes interband transition occur at low photon frequencies and thus, it is difficult to differentiate it from intraband transition. Here, we present a thorough study on decomposing the intraband and interband contribution to finite temperature dielectric functions of these bcc transition metals by performing electron-phonon and electron-electron interaction calculations, as well as ellipsometry experiments. In this work, the Drude model and interband transition theory are applied to quantitatively describe the intraband and interband transition, respectively. To accurately determine intraband transition, the relevant parameters for the Drude model, such as plasma frequency and electron relaxation time, are calculated from first-principles. The electron-electron interaction within the many-body theory and electron-phonon interaction within the density functional perturbation theory are calculated to obtain the electron relaxation time and intraband dielectric function at finite temperature. As for interband transition, the spin-orbit coupling is included and it shows nontrivial influence on the interband dielectric function of Mo and W, especially at low frequencies. To verify theoretical calculations, ellipsometry experiments are performed to measure dielectric functions of Cr, Mo, and W over the temperature range of 300–700 K and energy range of 0.08–4.8 eV. The experimental results are then fitted by the Drude model, and it shows that the electron-phonon interaction rather than electron-electron interaction dominates the frequency dependence of the relaxation time for transition metals Cr, Mo, and W.

One-Way Polarization Rotation by Indirect Interband Transitions

We report a theoretical demonstration of asymmetric polarized signal conversion by a sinusoidal-modulated taper polarization rotator. Based on indirect interband transition theory, periodical modulated taper introduces unidirectional conversion between quasi-TM/TE modes in a linear silicon-on-isolator system. The dependence on the sinusoidal perturbation parameters and the contribution of taper geometry are analyzed separately. The method and result presented here are expected to be valuable for the implication of on-chip isolation and optical signal processing.

High-lying interband transitions and optical properties ofInAs1−xSbxfilms

$\mathrm{In}{\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$ has been grown by liquid phase epitaxy on (100) InAs substrate with $x$ up to 0.11, and optical properties of the material have been investigated using spectroscopic ellipsometry at room temperature within $1.5--5.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The dielectric function $\ensuremath{\epsilon}(E)$ spectra that show well-defined structures associated with ${E}_{1}$, ${E}_{1}+{\ensuremath{\Delta}}_{1}$, and ${E}_{2}$ transitions have been observed and analyzed by a model dielectric function based on interband transition theory. Excellent agreement between the model calculation and the experimental data is achieved over the entire energy range studied. The transition energies ${E}_{1}$ and ${E}_{2}$, the spin-orbit splitting energy ${\ensuremath{\Delta}}_{1}$, and the broadening parameters as functions of Sb concentration are fit linearly.

Electronic and Optical Properties of Si/SiO2 Superlattices from First Principles: Role of Interfaces.

ABSTRACTThe observation of intense luminescence in Si/SiO2 superlattices (SLs) has lead to new theoretical research on silicon-based materials. We have performed first-principles calculations using three Si/SiO2 SL models in order to examine the role of interfaces on the electronic structure and optical properties. The first two models are derived directly from crystalline structures and have simple interfaces. These models have been studied using the full-potential, linearized-augmented-plane-wave method, in the local-density-approximation (LDA). The optical absorption within the interband transition theory (excluding excitonic effects) have been deduced. The Si(001)-SiO2 interface structure is shown to affect the optical behaviour. Following these observations, we have considered a more realistic, fully-relaxed model. The projector-augmented-wave method under the LDA is used to perform the structural relaxation as well as band structure and optical calculations. The role of confinement on the energy gap is studied by inserting additional silicon slabs into the supercell. Direct energy gaps are observed and the energy gap is found to decrease with increasing silicon slab thickness, as observed experimentally. The role of the interface has been considered in more details by studying the contribution to the energy gap of Si atoms having different oxidation patterns; partially oxidized Si atoms at the interface, as well as Si atoms inside the Si layer, are shown to contribute to the transitions at the energy gap.

Interband absorption in quantum wires. I. Zero-magnetic-field case.

We describe the theory of interband transitions in quasi-one-dimensional semiconductor structures. It is based on the effective-mass approximation and takes into account the mixing of the heavy-hole and the light-hole states in the valence band. The dipole matrix element for optical transitions between the valence-band and the conduction-band states is derived for different linear photon polarizations with respect to the wire orientation. The theory is applied to single wires and periodic arrays of coupled wires exhibiting spatially direct or indirect optical transitions. We also study the influence of sample imperfections by calculating the optical properties of a statistical ensemble of confinement potentials exhibiting random fluctuations.

Optical Properties of MBE-Grown Gainassb

ABSTRACTThe infrared optical absorption properties near and above the fundamental absorption edge of MBE grown undoped GaInAsSb quaternary semiconductor alloy deposited on GaSb and GaAs substrates have been measured and analyzed at room temperature by means of a Fourier Transform Infrared Spectrometer, and were found to be fully characterized by the interband transition theory and Urbach's rule. The optical band gap of MBE-GaInAsSb has been determined using a linear extrapolation of (ɑhv )2 as a function of the photon energy hv, and the refractive index n deduced from the interference pattern, which shows good agreement with the theory of Sadao Adachi's.

Inter-band transition probabilities and photon momentum

The theory of inter-band transitions is re-examined in the case of finite photon momentumq. New expressions for the joint density of states near critical points are derived. They give Van Hove’s expressions in both the limits of long and short wavelengths. The dispersion relation for the transverse dielectric functionɛ 2T due to inter-band processes is given explicitly and it is compared to that of the longitudinal dielectric functionɛ 2L . It is shown that in the limitq = 0ɛ 2T equalsɛ 2L even for anisotropic media. The possibility of an experimental evidence of the effects caused by a finite photon momentum on the shape of the optical absorption is discussed.