Electronic and Optical Properties of HgI2

1993 ◽  
Vol 302 ◽  
Author(s):  
Yia-Chung Chang ◽  
Hock-Kee Sim ◽  
R. B. James
Keyword(s):  
Electronic Structures ◽  
Electronic Band Structure ◽  
Scattering Data ◽  
Matrix Elements ◽  
Interband Transitions ◽  
Phonon Modes ◽  
Electronic Band ◽  
Optical Responses ◽  
Tetragonal Form ◽  
Excitonic Effects

ABSTRACTWe present theoretical studies of electronic structures, optical responses, and phonon modes of undoped HgI2 in its red tetragonal form. The electronic band structure is studied via an empirical nonlocal pseudopotential model, including the spin-orbit interaction. The electron and hole effective masses, optical matrix elements for interband transitions, and complex dielectric function are computed. Excitonic effects on the absorption coefficient near the fundamental band gap are included within the effectivemass approximation. The resulting absorption spectra and their polarization dependence are compared with experiment with favorable agreement. The phonon modes of HgI2 are studied with a microscopic model and a good fit to the neutron scattering data is obtained.

scholarly journals Normal-to-topological insulator martensitic phase transition in group-IV monochalcogenides driven by light

2020 ◽  
Vol 12 (1) ◽  
Author(s):  
Jian Zhou ◽  
Shunhong Zhang ◽  
Ju Li
Keyword(s):  
Phase Transition ◽  
Phase Change ◽  
Electronic Band Structure ◽  
Dielectric Medium ◽  
Group Iv ◽  
Electronic Band ◽  
Optical Responses ◽  
Martensitic Phase Transition ◽  
Linearly Polarized ◽  
Frequency Power

AbstractA material potentially exhibiting multiple crystalline phases with distinct optoelectronic properties can serve as a phase-change memory material. The sensitivity and kinetics can be enhanced when the two competing phases have large electronic structure contrast and the phase change process is diffusionless and martensitic. In this work, we theoretically and computationally illustrate that such a phase transition could occur in the group-IV monochalcogenide SnSe compound, which can exist in the quantum topologically trivial Pnma-SnSe and nontrivial $$Fm\bar 3m$$Fm3¯m-SnSe phases. Furthermore, owing to the electronic band structure differences of these phases, a large contrast in the optical responses in the THz region is revealed. According to the thermodynamic theory for a driven dielectric medium, optomechanical control to trigger a topological phase transition using a linearly polarized laser with selected frequency, power and pulse duration is proposed. We further estimate the critical optical electric field to drive a barrierless transition that can occur on the picosecond timescale. This light actuation strategy does not require fabrication of mechanical contacts or electrical leads and only requires transparency. We predict that an optically driven phase transition accompanied by a large entropy difference can be used in an “optocaloric” cooling device.

scholarly journals Inhomogeneous GaInNAs quantum wells: their properties and utilization for improving of p-i-n and p-n junction photodetectors

2018 ◽  
Vol 35 (4) ◽  
pp. 893-902
Author(s):  
D. Pucicki
Keyword(s):  
Electric Field ◽  
Quantum Wells ◽  
Electronic Structures ◽  
Electronic Band Structure ◽  
Total Content ◽  
Spatial Separation ◽  
Growth Direction ◽  
Field Vector ◽  
Absorption Efficiency ◽  
Electronic Band

Abstract A theoretical study of electronic structures and optical properties of GaInNAs/GaAs quantum wells has been performed. The inhomogeneous distributions of indium and nitrogen atoms along the growth direction were discussed as the main factors having significant impact on the QWs absorption efficiency. The study was performed by applying the band anticrossing model combined with the envelope function formalism and based on the material parameters which can be found in the literature. Indeed, the electronic band structure of 15 nm thick uniform Ga0.7In0.3N0.02As0.98/GaAs QW was computed together with electronic structures of several types of inhomogeneous QWs, with the same total content of In and N atoms. It was found that presented inhomogeneities lead to significant quantum wells potential modifications and thus to spatial separation of the electrons and holes wave functions. On the other hand, these changes have a significant impact on the absorption coefficient behavior. This influence has been studied on the basis of simulated photoreflectance spectra, which probe the absorption transitions between QW energy subbands. The electronic structure of inhomogeneous QWs under the influence of electric field has also been studied. Two different senses of electric field vector (of p-i-n and n-i-p junctions) have been considered and thus, the improvement of such types of QWs-photodetectors based on inhomogeneous GaInNAs QWs has been proposed.

Electronic Structures of P-Type Doped CuInS2

1996 ◽  
Vol 426 ◽  
Author(s):  
T. Yamamoto ◽  
H. Katayama-Yoshida
Keyword(s):  
Electronic Structures ◽  
Electronic Band Structure ◽  
Spherical Wave ◽  
Material Design ◽  
Electronic Band ◽  
Design Considerations ◽  
Band Structure Calculations ◽  
P Type ◽  
Structure Calculations ◽  
Codoping Method

AbstractWe have studied the electronic structures of CuIn(S0.875X0.125)2 (X=B, C, N, Si or P) based on the ab-initio electronic band structure calculations using the augmented spherical wave (ASW) method. We have clarified that the physical characteristics of the p-type doped CuInS2 crystals are mainly determined by a change in the strength of interactions between Cu and S atoms. On the basis of the calculated results, we discussed the material design considerations, such as controlling the strength of resistivity for p-type doped CulnS2 materials and converting the conduction type, from n-type to p-type by a codoping method.

scholarly journals Elastic and optical properties of sillenites: First principle calculations

2020 ◽  
Vol 557 (1) ◽  
pp. 98-104 ◽  
Author(s):  
Husnu Koc ◽  
Selami Palaz ◽  
Sevket Simsek ◽  
Amirullah M. Mamedov ◽  
Ekmel Ozbay
Keyword(s):  
Optical Properties ◽  
Electronic Structures ◽  
Density Functional ◽  
Electronic Band Structure ◽  
First Principle ◽  
Electronic Band ◽  
Functional Theory ◽  
First Principle Calculations ◽  
Optical Functions ◽  
The Density Functional Theory

In the present paper, we have investigated the electronic structure of some sillenites - Bi12MO20 (M = Ti, Ge, and Si) compounds based on the density functional theory. The mechanical and optical properties of Bi12MO20 have also been computed. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work. The band gap trend in Bi12MO20 can be understood from the nature of their electronic structures. The obtained electronic band structure for all Bi12MO20 compounds is semiconductor in nature. Similar to other oxides, there is a pronounced hybridization of electronic states between M-site cations and anions in Bi12MO20. Based on the obtained electronic structures, we further calculate the frequency-dependent dielectric function and other optical functions.

STRUCTURAL AND ELECTRONIC PROPERTIES OF α-TiNX (X:F, Cl, Br, I): AN AB INITIO STUDY

2011 ◽  
Vol 10 (01) ◽  
pp. 65-74 ◽  
Author(s):  
BAHADIR ALTINTAS
Keyword(s):  
Band Structure ◽  
Ab Initio ◽  
Halogen Atom ◽  
Electronic Band Structure ◽  
Geometry Optimization ◽  
Phonon Modes ◽  
Electronic Band ◽  
Band Structure Calculations ◽  
Structural And Electronic Properties ◽  
Structure Calculations

The electronic and lattice properties of α-TiNX (X:F, Cl, Br, I) were investigated from first principles. Ab initio calculations for geometry optimization, electronic band structure and zone-center phonon calculations have been carried out by using plane-wave pseudopotential method which is not examined before. From the electronic structure calculation, band gaps have been found as 1.23 eV, 0.955 eV, 0.897 eV for TiNF , TiNCl , TiNBr while there is no band gap for TiNI . This result can separate TiNI from other metal nitride halides which are semiconductor. Band structure calculations showed that increasing the electropositivity of halogen atom in TiNX systems decreasing the fermi energy level or in other words shift the valance bonds to higher energy. Also zone center phonon modes show that the vibrational frequencies are increasing by atomic number of halogens. Heavier halogen atom makes the system vibrate more slowly and as expected to reduce vibrational frequency.

scholarly journals On the feasibility of hearing electrons in a 1D device through emitted phonons

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Amit Verma ◽  
Reza Nekovei ◽  
Zahed Kauser
Keyword(s):  
Electronic Band Structure ◽  
Tight Binding ◽  
Radial Breathing Mode ◽  
Acoustic Phonons ◽  
Phonon Modes ◽  
Electronic Band ◽  
Ensemble Monte Carlo ◽  
Sensitivity Range ◽  
Effect Transistor ◽  
Active Channel

AbstractThis work investigates the vibrational power that may potentially be delivered by electron-emitted phonons at the terminals of a device with a 1D material as the active channel. Electrons in a 1D material traversing a device excite phase-limited acoustic and optical phonon modes as they undergo streaming motion. At ultra-low temperature (4 K in this study, for example), in the near absence of background phonon activity, the emitted traveling phonons may potentially be collected at the terminals before they decay. Detecting those phonons is akin to hearing electrons within the device. Results here show that traveling acoustic phonons can deliver up to a fraction of a nW of vibrational power at the terminals, which is within the sensitivity range of modern instruments. The total vibrational power from traveling optical and acoustic phonons is found to be in order of nW. In this work, Ensemble Monte Carlo (EMC) simulations are used to model the behavior of a gate-all-around (GAA) field-effect transistor (FET), with a single-wall semiconducting carbon nanotube (SWCNT) as the active channel, and a free-hanging SWCNT between two contacts. Electronic band structure of the SWCNT is calculated within the framework of a tight-binding (TB) model. The principal scattering mechanisms are due to electron–phonon interactions using 1st order perturbation theory. A continuum model is used to determine the longitudinal acoustic (LA) and optical (LO) phonons, and a single lowest radial breathing mode (RBM) phonon is considered.

Optical Characterization of Electronic Structure of CuInS2 and CuAlS2 Chalcopyrite Crystals

2011 ◽  
Vol 170 ◽  
pp. 21-24
Author(s):  
Ching Hwa Ho ◽  
Sheng Feng Lo ◽  
Ping Chen Chi ◽  
Ching Cherng Wu ◽  
Ying Sheng Huang ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Low Temperature ◽  
Band Structure ◽  
Electronic Band Structure ◽  
Interband Transition ◽  
Optical Characterization ◽  
Band Edge ◽  
Interband Transitions ◽  
Electronic Band

Electronic structure of solar-energy related crystals of CuInS2 and CuAlS2 has been characterized using thermoreflectance (TR) measurement in the energy range between 1.25 and 6 eV. The TR measurements were carried out at room (~300 K, RT) and low (~30 K, LT) temperatures. A lot of interband transition features including band-edge excitons and higher-lying interband transitions were simultaneously detected in the low-temperature TR spectra of CuInS2 and CuAlS2. The energies of band-edge excitonic transitions at LT (RT) were analysed and determined to be =1.545 (1.535) and =1.554 eV (1.545 eV) for CuInS2, and =3.514 (3.486), =3.549 (3.522), and =3.666 eV (3.64 eV) for CuAlS2, respectively. The band-edge transitions of the and excitons are originated from the sulfur pp transitions in CuInS2 and CuAlS2 separated by crystal-field splitting. Several high-lying interband transitions were detected in the TR spectra of CuInS2 and CuAlS2 at LT and RT. Transition origins for the high-lying interband transitions are evaluated. The dependence of electronic band structure in between the CuInS2 and CuAlS2 is analysed and discussed.

scholarly journals Machine Learning Chemical Guidelines for Engineering Electronic Structures in Half-Heusler Thermoelectric Materials

Research ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-8 ◽  
Author(s):  
Maxwell T. Dylla ◽  
Alexander Dunn ◽  
Shashwat Anand ◽  
Anubhav Jain ◽  
G. Jeffrey Snyder
Keyword(s):  
Machine Learning ◽  
Valence Band ◽  
Electronic Structures ◽  
Electronic Band Structure ◽  
Valence Band Maximum ◽  
Electronic Band ◽  
Band Maximum ◽  
Orbital Phase ◽  
Valence Bands ◽  
P Type

Half-Heusler materials are strong candidates for thermoelectric applications due to their high weighted mobilities and power factors, which is known to be correlated to valley degeneracy in the electronic band structure. However, there are over 50 known semiconducting half-Heusler phases, and it is not clear how the chemical composition affects the electronic structure. While all the n-type electronic structures have their conduction band minimum at either the Γ- or X-point, there is more diversity in the p-type electronic structures, and the valence band maximum can be at either the Γ-, L-, or W-point. Here, we use high throughput computation and machine learning to compare the valence bands of known half-Heusler compounds and discover new chemical guidelines for promoting the highly degenerate W-point to the valence band maximum. We do this by constructing an “orbital phase diagram” to cluster the variety of electronic structures expressed by these phases into groups, based on the atomic orbitals that contribute most to their valence bands. Then, with the aid of machine learning, we develop new chemical rules that predict the location of the valence band maximum in each of the phases. These rules can be used to engineer band structures with band convergence and high valley degeneracy.

Radiative Properties of GaAs From First Principles Calculations

2008 ◽  
Author(s):  
Hua Bao ◽  
Xiulin Ruan
Keyword(s):  
Band Structure ◽  
Dielectric Function ◽  
First Principles ◽  
Electronic Band Structure ◽  
Golden Rule ◽  
Radiative Properties ◽  
Initial Structure ◽  
Phonon Modes ◽  
Electronic Band ◽  
Near Ir

Spectral reflectance of GaAs from infrared (IR) to ultra-violet (UV) bands is calculated from first principles. We first calculate the spectral dielectric function which is determined by the response of GaAs to external electromagnetic field. Two mechanisms exist for different wavelengths, namely, phonon absorption in the far-IR region and the electronic absorption in the near-IR to UV region. With plane-wave pseudopotential method, we determined the dielectric function of GaAs with the the initial structure as the only input. For the far-IR region, phonon calculations are carried out. By analyzing the phonon modes, low-frequency dielectric constant is calculated. For the near-IR to UV band, the electronic band structure of GaAs is calculated, and the imaginary part of the dielectric function is determined from the band structure using Fermi’s Golden rule. The real part of spectral dielectric function is then derived from Kramer-Kronig transformation. The reflectance is then calculated using Maxwell’s equations.

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