The ab initio prediction of band gaps for solids is important for fundamental and practical reasons. Many approaches exist to remedy the "band gap problem" in Density Functional Theory (DFT) in which band gaps are severely underestimated. We recently proposed the ?-sol ...
NASA Astrophysics Data System (ADS)
Band-edge shifts induced by the electron-phonon interaction are calculated for HgCdTe alloys and various semiconductor compounds starting from accurate zero-temperature band structures. The calculated temperature variation of gaps agrees with experiments to better than 10% in all materials except InAs and InSb ...
This animation shows band populations as a function of temperature in an n-type semiconductor. Note that the Fermi-energy actual shifts position in the band gap and is not accurately depicted here. The video shows the conduction bond and valence bond separated by a band gap ...
NSDL National Science Digital Library
In this paper we motivate the use of a novel high order time domain vector finite element method that is of arbitrary order accuracy in space and up to 5th order accurate in time; and in particular, we apply it to the case of photonic band-gap (PBG) struc...
National Technical Information Service (NTIS)
Thermophotovoltaic cells with a range of band gaps are modeled under a variety of illumination conditions, including a range of source temperatures and a variable degree of spectral control. Thus, the balance between the requirements of high power densities and high efficiencies can be investigated. The influence of elevated cell temperatures, cell ...
A semiempirical method that yields accurate band gaps and atomic positions in sp{sup 2}-hybridized, organic, semiconducting polymers has been obtained. This method is a tight-binding calculation where most of the parameters are determined via an ab initio local density approximation method leaving only {pi}-{pi} interactions to be ...
Energy Citations Database
The inhibition in wave propagation at band gap energies plays a central role in many areas of technology such as electronics (electron gaps), nanophotonics (light gaps) and phononics (acoustic gaps), among others. Here we demonstrate that metal surfaces featuring free-electron-like ...
Theoretical investigation of the defect energy levels in band gap for ZnO is of great importance to understand the photoluminescence (PL) spectrum in experiment. However, the "band-gap" problem in the density functional calculations leads to incorrect evaluation of the defect levels inside the band ...
PubMed
As a stepping point to predicting band gaps and electronic structure of more complicated materials based on alkaline and post-transition metal oxides, we examine the valence structure of these simple binary oxides using both high resolution X-ray emission spectroscopy and a variety of density functional theory calculations. We confirm that the new modified ...
Low temperature photoluminescence of GaP and GaAs was investigated under conditions of uniaxial strain generated using shock and ramp wave loading along the [100], [111], and [100] orientations. In GaP, the exact band gap shifts were measured up to 5 GPa longitudinal stress and accurate optical ...
The cadmium and magnesium indium sulfides are medium-gap semiconductors demonstrating a propensity to form intermediate band materials when doped with transition metals. The inherent structural diversity exhibited by M+2In2S4 thiospinels and related AB2X4 compounds often precludes definitive experimental determination of the band-gap ...
... Title : D-Band Surface States on Wide Band Gap Insulators. A Conceptual Model for Surface States and Catalysis on d-Band Perovskites. ...
DTIC Science & Technology
We present parameter-free calculations of electronic properties of InGaN, InAlN, and AlGaN alloys. The calculations are based on a generalized quasichemical approach, to account for disorder and composition effects, and first-principles calculations within the density functional theory with the LDA-1/2 approach, to accurately determine the band ...
Semiconductor alloy heterostructures are the backbone of optoelectronic devices. Among the most important parameters that determine the utility of heterostructure devices are the valence and conduction band offsets. Although DFT with standard functionals such as LDA or PBE does an acceptable job for valence band offsets, it fails to predict ...
The band energy differences of solids calculated with screened hybrid density functionals, such as the functional of Heyd-Scuseria-Ernzerhof (HSE), reproduce experimental band gaps with a high degree of accuracy. This unexpected result is here rationalized by observing that band energy differences obtained from ...
Using a total energy method with detailed control of electrostatic boundary conditions, esp. the chemical potential for net charge, the computed charge transition levels of simple intrinsic defects in GaAs within density functional theory are presented. The levels are demonstrated to be converged with supercell size, and largely insensitive to the functionals and pseudopotentials used. The results ...
A comprehensive study of band gaps in CdXP2 (X = Si, Ge and Sn) compounds has been presented using full potential linearized augmented plane wave (FPLAPW) method. The exchange effects are taken into account by an orbital independent modified Becke-Johnson (MBJ) potential as coupled with correlation term given by Local Density Approximation (LDA) for all ...
This task will provide information on the radiation hardness of wide band gap ... Wide band gap electronic devices are a new technology with a number of ...
NASA Website
band-gap laser radiation with a view towards its applicability in ... below band -gap laser radiation confines most of the energy of the laser pulse in the ...
band and the top of the valence band is the band gap Eg; no electrons are ...... ts all the further the primartJ elctron. Band gap can penetrate. ...
... SPIN-ORBIT BAND ON THE BAND GAPS OF InAs/GaSb SUPERLATTICES BEYOND THE STANDARD ENVELOPE-FUNCTION APPROXIMATION ...
We present the GW band structure of ZnO in its wurtzite (WZ), zincblende (ZB) and rocksalt (RS) phases at the ? point, calculated within the GW approximation. We have used a Zn20+ pseudopotential which is essential for the adequate treatment of the exchange interaction in the self-energy. The accuracy of the pseudopotential used is also discussed. The effect of the p�d ...
Two improvements for the solution of Maxwell's equations in periodic dielectric media are introduced, abandoning the plane-wave cutoff and interpolating the dielectric function. These improvements permit the accurate study of previously inaccessible systems. Example calculations are discussed, employing a basis of ~106 plane waves for which these two improvements reduce both ...
We report first principles analysis of the band gap Eg of ternary group-III nitride InxGa1-xN in both the wurtzite and zincblende form, within the linear muffin-tin orbital (LMTO) density functional theory method. We have implemented the semilocal modified Becke-Johnson (MBJ) exchange potential to accurately determine the ...
Portable radiometers are commonly used in remote sensing applications for studying vegetation, soil, minerals, etc. However, we propose and demonstrate, for the first time, the applicability of this radiometer for high-resolution in situ band gap measurements of materials. The excitation source can be any white light source such as sun or tungsten halogen ...
We examine the electronic structure of the family of ternary zinc spinel oxides ZnX2O4 (X=Al, Ga and In). The band gap of ZnAl2O4 calculated using density functional theory (DFT) is 4.25 eV and is overestimated compared with the experimental value of 3.8-3.9 eV. The DFT band gap of ZnGa2O4 is 2.82 eV and is ...
... Accession Number : AD0664784. Title : THE REALIZATION OF A WIDE BAND GAP EMITTER TRANSISTOR. Descriptive ...
... ADP013042 TITLE: Luminescence Enhancement in Indirect Band-Gap Semiconductors With Quantum Confinement Structures ...
The performance of novel devices, e.g., HEMTs based on semiconductor heterostructures, depend strongly on their conduction and valence band-offsets. However, conventional density functional theory based on LDA and GGA fails for narrow-gap semiconductors such as InAs, predicting it to be a metal. An accurate treatment of such systems ...
Cd{sub 1-x}Zn{sub x}Te alloys have been studied by surface photovoltage spectroscopy (SPS) and energy dispersive spectroscopy (EDS). The analyses of surface photovoltage spectra have been perfomed at near and above band gap energies. Surface recombination effects on the surface photovoltage have been investigated. SPS analyses of Cd{sub 1-x}Zn{sub x}Te ...
Photochemical watersplitting can potentially be a future sustainable energy source, converting sunlight and water into hydrogen. However, in order to have highly efficient devices materials are needed that absorb a large proportion of the solar spectrum while at the same time having valence and conduction bands that straddle the hydrogen and oxygen evolution redox potentials. ...
Non-crystalline PBG materials have received increasing attention recently and sizeable PBGs have been reported in quasi-crystalline structures or even in disordered structures. Band calculations for periodic structures produce accurate dispersion relations in them and refraction properties at their surfaces. However, band calculations ...
Calculations of formation energies and charge transition levels of defects routinely rely on density functional theory (DFT) for describing the electronic structure. Since bulk band gaps of semiconductors and insulators are not well described in semilocal approximations to DFT, band-gap correction schemes or advanced theoretical ...
The band structures and effective masses of III-V semiconductors (InP, InAs, InSb, GaAs, and GaSb) are calculated using the GW method, the Heyd, Scuseria, and Ernzerhof hybrid functional, and modified Becke-Johnson combined with the local-density approximation (MBJLDA)�a local potential optimized for the description of the fundamental band ...
We present a hybrid density functional theory (DFT) study of doping effects in ?-Fe(2)O(3), hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike ...
We present a hybrid density functional theory (DFT) study of doping effects in ?-Fe2O3, hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike the ...
An overview of the theoretical and experimental efforts in obtaining a photonic band gap, a frequency band in three-dimensional dielectric structures in which electromagnetic waves are forbidden, is presented.
... in miniaturized photonic band gap materials. ... Center, US Army Aviation and Missile ... PHOTONICS, *BAND GAPS, INTERACTIONS, PARAMETERS ...
band gap closes, forming a Dirac point, and then reopens as conventional band gap. Recent physics research shows how spin-orbit coupling can rearrange electronic bands in a solid...
Science.gov Websites
Contrary to previous reports, we show that the conventional GW (the so-called G?W?) approximation can be used to calculate accurately the experimental band gap (?3.6??eV) of ZnO. The widely discussed underestimate of the quasiparticle gap of ZnO within the GW method is a result of an inadequate treatment of the ...
There is strong support in favor of an unusual s{+-} superconducting state in the recently discovered iron-based superconductors in which the gap parameter has opposite signs in different bands. In this case, scattering between different bands by impurities has a pair-breaking effect and introduces states inside the ...
The screened hybrid functional, HSE, used in density functional theory (DFT) has been gaining traction recently for its predictive powers of the band structure in bulk semiconductors. It is natural to assume that these accurate results would carry over to alloy semiconductors, but little work has been done to confirm this. We recently investigated the ...
We calculate the band structures of kesterite and stannite Cu2ZnSnS4 and Cu2ZnSnSe4, using a state-of-the-art self-consistent GW approach. Our accurate quasiparticle states allow to discuss: the dependence of the gap on the anion displacement; the key-role of the nonlocality of the exchange-correlation potential to obtain good ...
The quasiparticle band structure of bismuth telluride (Bi2Te3) , an important thermoelectric material that exhibits topologically insulating surface states, is calculated from first principles in the GW approximation. The quasiparticle energies are evaluated in fine detail in the first Brillouin zone using a Wannier-function interpolation method, allowing the ...
Density-functional methods are used to analyze the scaling of discrete oligomeric ?-electron conducting molecules towards idealized isolated polymer chains, treated in periodic boundary conditions. The band gaps of a series of conjugated oligomers of incrementally increasing lengths exactly fit a nearly-free-electron molecular-orbital picture and exhibit a ...
We report on low-temperature magnetoluminescence determinations of bandstructure parameters for an 8.5nm-wide n-type In{sub 0.20}Ga{sub 0.80}As/GaAs strained single-quantum well structure. We find that the conduction-band is almost parabolic, with its mass varying from 0.067m{sub 0} at zone center to 0.069m{sub 0} at a Fermi energy E{sub f} {approx} 50 meV, and that the ...
{sm_bullet}HF/DFT are one-particle approximation to the Schrodinger equation {sm_bullet} The one-particle, mean field approaches are what lead to the nonlinear eigenvalue problem {sm_bullet} DFT includes a parameterized XC functional that reproduces many-electron effects -Very accurate ground state structures and energies - Problematic for excited states, ...
Integrating optoelectronic functionalities directly into the mature Silicon-Germanium technology base would prove invaluable for many applications. Unfortunately, both Si and Ge display indirect band-gaps unsuitable for optical applications. It was previously shown (Zachai et al. PRL 64 (1990)) that epitaxially grown [(Si)n(Ge)m]p (i. e. a single repeat unit) grown on Si can ...
The effect of strain on the compositional and optical properties of a set of epitaxial single layers of InxGa1-xN was studied. Indium content was measured free from the effects of strain by Rutherford backscattering spectrometry. Accurate knowledge of the In mole fraction, combined with x-ray diffraction measurements, allows perpendicular strain (?zz) to be evaluated. Optical ...
This letter provides clear insight into the interplay between electron and hole characteristics of carriers within the forbidden gap during the band-to-band tunneling process, taking graphene-nanoribbons as an example. Accurate numerical models are presented and analytical formulas for tunneling probabilities are derived for both ...
The idea of the linear combination of atomic orbitals method, well known from the study of electrons, is extended to the classical wave case. The Mie resonances of the isolated scatterer in the classical wave case are analogous to the atomic orbitals in the electronic case. The matrix elements of the two-dimensional tight-binding (TB) Hamiltonian are obtained by fitting to {ital ab initio} ...
The thermal fluctuation of the intermolecular hopping integral in the series of polyacene crystals (naphthalene, anthracene, tetracene, pentacene) was evaluated computationally using a combined molecular dynamics and quantum chemistry approach. It was shown that these large fluctuations can manifest themselves in a temperature-dependent relatively broad tail of the density of states extending from ...
A plurality of active gain material is disposed in an active interface portion of a dielectric band-gap cladding confinement region adjacent to a dielectric core of a photonic band-gap crystal fiber, wherein during operation, the plurality of active gain ...
This report demonstrates how the MPB (MIT Photonic-Bands) package can be efficiently used to compute and collect data for plotting gap maps for photonic crystals (photonic band-gap materials). MATLAB is used for transforming the gap map data (output from ...
Two-polariton spontaneous emission is studied in dispersive and photonic band-gap materials doped with a three-level atom in the cascade configuration. It is found that when the two resonance frequencies of the top and middle excited states of the atom lie outside the band gap, an emission of two polaritons can cause an interference ...
The author investigates the characteristics of magnetic resonance band gaps for split ring structures. Resonance band gap width is related to the discrepancy of resonance frequency at two different Bloch wavelength scales. Large band gaps are achieved by lowering the ...
In this paper, a finite element method based on the ABAQUS code and user subroutine is presented to evaluate the propagation of acoustic waves in the two-dimensional phononic crystals with Archimedean-like tilings. Two systems composed of cylinder scatters embedded in a host in Ladybug and Bathroom lattices are considered. Complete and accurate band ...
The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band ...
... band gap semiconductors relevant to efficient thermoelectric power generation and ... We assessed the potential of the nanocrystal-derived materials ...
An accurate ab initio full potential linear muffin-tin orbital method has been used to investigate the structural, electronic and optical properties of BP, BAs and their (BP)n/(BAs)n superlattices (SLs). The exchange-correlation potential is treated with the local density approximation of Perdew and Wang (LDA-PW). The calculated structural properties of BP and BAs compounds ...
The changes in energetic, structural, and electronic properties of the metallic (5,5) single-walled carbon nanotube (SWNT) with the degree of sidewall covalent functionalization of CCl(2) are investigated extensively by using density functional theory calculations. The saturation concentration of CCl(2) covalent functionalization is predicted to be 33.3%. The cycloadducts always adopt an open ...
... Title : Variable Band Gap Materials for Thermophotovoltaic ... Holes were drilled through the substrate using a laser ... were fabricated by drilling a hole ...
... Accession Number : ADA179941. Title : Theory of Below-Band-Gap Photoluminescence in a Gallium Arsenide Doping Superlattice. ...
When an extrinsic, direct band-gap semiconductor sample is irradiated by photons of an energy higher
NASA Technical Reports Server (NTRS)
... The overall objective of this STTR program is ... can achieve their technology transfer objectives ... for next generation photonic band gap technologies. ...
... Accession Number : ADA119264. Title : Optical Properties of Small Band Gap Semiconductors Subject to Laser Excitation. ...
... success producing an appreciable density of Rb ... We systematically characterized low-loss photonic band-gap ... of the propagating mode and when ...
... Accession Number : ADD852872. Title : Non-Avalanche Dielectric Breakdown in Wide-Band-Gap Insulators at DC and Optical Frequencies. ...
Jan 22, 2011 ... Abstract: We discuss a simple ID model of the modification of Planck blackbody radiation by photonic band-gap materials (PBGs). ...
This is because a solar cell can only generate cummt if the wavelength of the incident light is greater than the band gap energy of the semiconductor. ...
The optical properties of solution-grown ZnO nanorods were investigated using photoluminescence and cathodoluminescence. The as-grown nanorods displayed a broad yellow-orange sub-band-gap luminescence and a small near-band-gap emission peak. The sub-band-gap luminescence can only be observed when exciting above ...
... wide band gap materials are irradiated with pulsed UV laser light. In model wide bandgap materials such as single crystal alkali halides and MgO ...
... Abstract : We present fabrication of 3D photonic band gap woodpile crystals from photosensitive chalcogenide glass with the help of interference ...
... Electromagnetic Band Gap (EBG) structures. ... Descriptors : *AIRCRAFT, *SYNTHETIC APERTURE RADAR ... ARRAYS, *BAND GAPS, *HIGH GAIN ...
... Accession Number : ADD451196. Title : CORE-VALENCE BAND TRANSITIONS IN WIDE-GAP IONIC CRYSTALS. Corporate Author : ...
Key words, band-gap engineering, amorphous, III-nitrides, scandium nitride, ellipsometry. Subject Classification. Material science. 1. Introduction. ...
... Title : Band Gaps and Asymptotic Behaviour of Continued Fraction Coefficients (Comportement Asymptotique des Coefficients de Fraction Continue ...
Physical Optics Corporation (POC) proposed a new concept of creating photonic band gaps on optical waveguides for the realization of low loss bands. These low loss bands are particularly useful for the realization of high density optical interconnection n...
... Descriptors : *PHOTONICS, DIELECTRICS, DIFFRACTION, PATTERNS, RUSSIA, ENERGY BANDS, FOURIER ANALYSIS, BAND GAPS. ...
... CRYSTAL DEFECTS, DEUTERIUM, DOPING, PHONONS, BAND THEORY OF SOLIDS, ELECTRON IRRADIATION, VIBRATIONAL SPECTRA. ...
... Vertical transitions between deep levels and the free bands involve energy changes of the order of half the band gap and take place mainly in ...
Lamb wave propagation in a surface-stubbed phononic-crystal plate is investigated numerically and experimentally. Results show that the complete band gaps and flat bands of elastic waves exist in the structure. By using laser ultrasonic techniques, the experimental measurements demonstrate the evidence of the band ...
Photonic crystals are structures with spatially periodic variations in optical properties. These periodic variations give rise to optical band structures (analogous to electronic band structure in solids) which can possess photonic band gaps: bands of frequency for which electromagnetic waves ...
Because of its narrow gap, InSb has considerable promise as a quantum well material because its small conduction-band mass gives it the highest room temperature electron mobility among the III-V materials. We present experiments and calculations for the magneto-absorption spectra in a strained, narrow gap InSb/AlInSb parabolic quantum ...
A useful technique is presented for calculating the approximate behavior of electromagnetic wavepackets in a periodic dielectric medium. The technique produces an operator equation which describes the time evolution of the envelope of the wave packet. The operator equation is shown to be equivalent to the Helmholtz equation in linear, isotropic, homogeneous media and to a Schr�dinger-like ...
Electromodulation spectroscopy (photoreflectance and electroreflectance) is an excellent technique to study optical transitions in quantum well (QW) structures but the development of this technique in the midinfrared spectral region is still limited due to various reasons. In this work we report our recent progress in the development of contactless electroreflectance spectroscopy in midinfrared ...
Accurate full-potential self-consistent linearized augmented-plane-wave (FLAPW) calculations have been carried out for hexagonal boron nitride. The resulting energy-band structure indicates that this material is an indirect-gap insulator and shows the existence of two unoccupied interlayer bands, similar to those ...
Hybrid density functional theory/molecular mechanics (DFT/MM) methods have been used to investigate the effects of vanadium substitution in ETS-10. Models have been developed to contain varying concentrations of V(IV) and V(V) within the O-M-O (M = Ti, V) chain. Most of the V-substituted models have a localized mid-gap state. The occupation of this localized state depends upon ...
The optimization of the procedure to grow accurate amounts of amorphous silicon and germanium by chemical vapor deposition (CVD) free of contamination in opals has been performed. The samples have been optically characterized and results agree with theoretical calculations of band structures. Multilayer systems of both semiconductors have been fabricated. ...
wide band gap ZnO and GaN semiconducting nanowires by fabricating the devices with good Ohmic contacts American Institute of Physics. DOI: 10.1063/1.3067868 Wide band gap semiconducting nanowires such as ZnO of the carrier concentration of highly doped wide band gap ...
E-print Network
In the presence of an intense ion acoustic wave, the energy-momentum dispersion relation of plasmons is strongly modified to exhibit a band gap structure. The intensity of an ion acoustic wave might be measured from the band gap width. The plasmon band gap can be used to ...
... MATERIALS, GLASS, ILLUMINATION, SPAIN, CHALCOGENS, ARSENIC COMPOUNDS, SELENIUM COMPOUNDS, VITRIFICATION, BAND GAPS ...
We propose a scheme of employing quantum interference and coherence in an optical medium with coupled electromagnetic fields to create a photonic band gap. A variable photonic band gap is achieved by the cross-phase-modulation of two counterpropagating coupling fields on a weak probe pulse. The proposed photonic ...
