Showing papers on "Band gap published in 1991"
TL;DR: In this article, the size effect on the optical and photophysical properties of semiconductor clusters has been studied in the condensed phase and the current status of materials synthesis and the prospect for making monodisperse clusters of well-defined surfaces has been discussed.
Abstract: Recent advances in the synthesis of semiconductor clusters open a doorway for the systematic study of size-dependent cluster properties in the condensed phase. This article focuses on the size effect on the optical and photophysical properties. The authors first introduce fundamental concepts and proceed to a discussion of recent progress toward the understanding of the quantum size effect and dielectric confinement effect. They then discuss the current status of materials synthesis and the prospect for making monodisperse clusters of well-defined surfaces.
1,892 citations
TL;DR: In this article, it was shown that a two-dimensional quantum confinement (quantum wire) in the very narrow walls between the pores not only explains the change in band gap energy but also may also explain the dissolution mechanism that leads to porous silicon formation.
Abstract: Porous silicon layers grown on nondegenerated p‐type silicon electrodes in hydrofluoric acid electrolytes are translucent for visible light, which is equivalent to an increased band gap compared to bulk silicon. It will be shown that a two‐dimensional quantum confinement (quantum wire) in the very narrow walls between the pores not only explains the change in band‐gap energy but may also be the key to better understanding the dissolution mechanism that leads to porous silicon formation.
1,705 citations
TL;DR: In this article, a new three-parameter fit to the temperature dependence of semiconductor band gaps was proposed, based on the semi-empirical Varshni equation.
Abstract: In this letter we advocate the use of a new three-parameter fit to the temperature dependence of semiconductor band gaps. This fitting improves upon the semi-empirical Varshni equation* both numerically, since it gives better fits to the data, and theoretically, since the parameters of the fit may be related to an intrinsic interaction of semiconductors, namely the electron-phonon coupling. Similar expressions to ours have appeared in the literature2T3 but the practical and theoretical justification of this kind of data fit have not previously been worked out in detail. We emphasize that our approach is empirical: we aim simply to describe the data as well as possible with the minimum number of free parameters. The Varshni relation for the temperature dependence of semiconductor band gaps is Eg(T)=Eo--cYT2/(T+pA (1)
1,010 citations
TL;DR: In this article, a two-hand model is used to calculate the scaling and spectrum of the nonlinear absorption of semiconductors and wide-gap optical solids, and the bound electronic nonlinear refractive index n/sub 2/ is obtained using a Kramers-Kronig transformation.
Abstract: A two-hand model is used to calculate the scaling and spectrum of the nondegenerate nonlinear absorption. From this, the bound electronic nonlinear refractive index n/sub 2/ is obtained using a Kramers-Kronig transformation. The authors include the effects of two-photon and Raman transitions and the AC Stark shift (virtual band blocking). The theoretical calculation for n/sub 2/ shows excellent agreement with measured values for a five-order-of-magnitude variation in the modulus of n/sub 2/ in semiconductors and wide-gap optical solids. Beam distortion methods were used to measure n/sub 2/ in semiconductors. The observations result in a comprehensive theory that allows a prediction of n/sub 2/ at wavelengths beneath the band edge, given only the bandgap energy and the linear index of refraction. Some consequences for all-optical switching are discussed, and a wavelength criterion for the observation of switching is derived. >
956 citations
TL;DR: Three-dimensionally periodic dielectric structures, photonic crystals, possessing a forbidden gap for electromagnetic wave propagation, a photonic band gap, are known, and it is now possible to make high-Q electromagnetic cavities of \ensuremath{\sim}1 cubic wavelength, for short wavelengths at which metallic cavities are useless.
Abstract: Three-dimensionally periodic dielectric structures, photonic crystals, possessing a forbidden gap for electromagnetic wave propagation, a photonic band gap, are now known. If the perfect 3D periodicity is broken by a local defect, local electromagnetic modes can occur within the forbidden band gap. Addition of extra dielectric material locally, inside the photonic crystal, produces ``donor'' modes. Conversely, local removal of dielectric material from the crystal produces ``acceptor'' modes. It is now possible to make high-Q electromagnetic cavities of \ensuremath{\sim}1 cubic wavelength, for short wavelengths at which metallic cavities are useless. These new dielectric cavities can cover the range from mm waves to UV wavelengths.
768 citations
TL;DR: Large absorptions have been observed for the first time in GaAs/AlGaAs multiquantum wells (MQW) by West and Eglash by noting the dipole matrix elements associated to these intersubband transitions (ISBT) have the same order of magnitude as the quantum well width leading to extremely large absorption.
Abstract: Thanks to the recent progresses in epitaxy techniques, it is now possible to grow alternating layers of semiconductors with different band gap energies with a thickness control down to one atomic layer. It is now well established that these systems behave, as far as the electron motion is concerned, as a succession of potential barriers and wells. If the width of the potential well is less than the deBroglie wavelength of the electrons in the material (e.g. less than ≈15 nm in GaAs), the motion of the electrons may be considered, at sufficiently low temperature, as quantized in the direction normal to the growth axis1. The electrons are quantized into subbands where their wavefunctions in the growth direction have the form of envelope functions with an extension equal to the well width, i.e. in the few nanometer range. Electromagnetic waves may induce electronic transitions between these subbands. The dipole matrix elements associated to these intersubband transitions (ISBT) have the same order of magnitude as the quantum well width leading to extremely large absorption. These large absorptions have been observed for the first time in GaAs/AlGaAs multiquantum wells (MQW) by West and Eglash2.
424 citations
TL;DR: In this paper, the spectral distribution of the emitted light was measured−in situ−during the anodic oxidation step, and recorded spectra show a maximum which shifts continuously from red‐orange at the beginning of the process towards the yellow range.
Abstract: Porous silicon/silicon structures under anodic oxidation conditions give rise to an electroluminescence phenomenon in the visible range. Using an optical multichannel analyzer the spectral distribution of the emitted light was measured−in situ−during the anodic oxidation step. Recorded spectra show a maximum which shifts continuously from red‐orange at the beginning of the process towards the yellow range. The visible emission well above the band gap of bulk silicon is attributed to a quantum size effect in the very small size (5–20 A) silicon island which constitutes the porous silicon skeleton. The light emission is interrupted when the current flow stops due to the formation of a continuous oxide layer at the porous silicon/silicon interface.
413 citations
TL;DR: In this paper, estimates of valence-band and conduction-band offsets for lattice-matched and pseudomorphic strained heterostructures of six technologically important III-V quaternary alloys are presented.
Abstract: Estimates of valence-band and conduction-band offsets for lattice-matched and pseudomorphic strained heterostructures of six technologically important III-V quaternary alloys are presented. Valence-band offsets are obtained via interpolation of the theory-based results of Van de Walle's 'model-solid' approach for the binary constituents. Estimates for band gap differences are obtained via interpolation of the experimental band gap energies of the ternary constituents. Adding the valence-band offset and band gap difference gives an estimate of the conduction-band offset. Band-edge effective masses at Gamma are determined from a linear interpolation of the effective masses of the binary constituents, obtained from self-consistent ab initio band structure calculations. Results are shown to agree well with the outcome of experiments.
399 citations
TL;DR: It is argued that the assessment of the accuracy of the conduction-band states should rely mainly on the reproduction of major structures in the optical-absorption curves rather than on the size of the band gap.
Abstract: The electronic structures, the charge-density distribution, and the total energies of boron nitrides (BN) in the hexagonal, cubic, and wurtzite structures are studied by first-principles self-consistent local-density calculations. For the ground-state properties, the band structures, the equilibrium lattice constants, the bulk modulus and their derivatives, and the cohesive energy are in good agreement with other recent calculations and with experimental data. The relative stabilities and possible phase transitions among these three phases are discussed. The linear optical properties of these three crystals are also calculated and compared with the available measurements. For hexagonal BN, all the structures in the electron-energy-loss function as measured by inelastic electron scattering have been reproduced by the calculation. For cubic BN, the calculated dielectric functions is also in good agreement with the reflectance data. For wurtzite-structure BN, no optical data are available for comparison. These results are discussed in the context of crystal structure and bonding in these three crystals. Based on the analysis of the calculated and measured optical data on cubic and hexagonal BN, it is argued that the assessment of the accuracy of the conduction-band states should rely mainly on the reproduction of major structures in the optical-absorption curves rather than on the size of the band gap. The accuracy of the higher conduction-band states as calculated by the local-density theory is strongly energy and momentum dependent. Furthermore, a determination of the optical gap is complicated by the different roles of the direct and indirect transitions, and by the difficult task of extrapolating data to the low-frequency region.
389 citations
TL;DR: In this article, the authors presented simple but accurate closed form equations for band gap narrowing (BGN) for n and p type, Si, Ge, GaAs and GexSi1−x alloys and strained layers.
Abstract: This paper presents simple but accurate closed form equations for Band Gap Narrowing (BGN) for n and p type, Si, Ge, GaAs and GexSi1−x alloys and strained layers The equations are derived by identifying the four components of BGN: exchange energy shift of the majority band edge, correlation energy shift of the minority band edge and impurity interaction shifts of the two band edges In the simple parabolic band approximation, the BGN is determined by the effective masses of the carriers and the relative permittivity of the semiconductor For real semiconductors, known corrections due to anisotropy of the bands, due to multi-valleys in a band and due to interactions between sub-bands are used The values of BGN for n Si, n Ge and n and p GaAs calculated using this simple formulation agree closely with the theoretical values calculated by other authors using advanced but complex many body methods and the Random Phase Approximation for screening effects For p Si and p Ge ours appear to be the first calculations taking all interactions into account Experimental values of BGN for all semiconductors except for p Ge for which no data could be found, are also in very good agreement with our theory The Fermi level for n and p Si and p GaAs is determined using the published luminescence data In heavily doped p type semiconductors, the values are found to be considerably smaller than those calculated using the known values of the effective density of states The values of apparent BGN for n and p Si and p GaAs calculated using experimentally determined Fermi levels are in remarkably good agreement with the experimental values derived from device measurements All results are presented in a form which lends itself to numerical computer simulation studies
376 citations
TL;DR: Strong self-dressing of the atom by its own localized radiation field leads to anomalous Lamb shifts and a splitting of the excited atomic level into a doublet when the transition frequency lies near a photonic band edge.
Abstract: We describe the quantum electrodynamics of photons interacting with hydrogenic atoms and molecules in a class of strongly scattering dielectric materials. These dielectrics consist of an ordered or nearly ordered array of spherical scatterers with real positive refractive index and exhibit a complete photonic band gap or pseudogap for all directions of electromagnetic propagation. For hydrogenic atoms with a transition frequency in the forbidden optical gap, we demonstrate both the existence and stability of a photon-atom bound state. For a band gap to center frequency ratio \ensuremath{\Delta}\ensuremath{\omega}/${\mathrm{\ensuremath{\omega}}}_{0}$\ensuremath{\sim}5%, the photon localization length ${\ensuremath{\xi}}_{\mathrm{loc}}$\ensuremath{\ge}10L, where L is the lattice constant of dielectric array. This strong self-dressing of the atom by its own localized radiation field leads to anomalous Lamb shifts and a splitting of the excited atomic level into a doublet when the transition frequency lies near a photonic band edge. We estimate the magnitude of this splitting to be ${10}^{\mathrm{\ensuremath{-}}6}$ at the vacuum transition energies.
TL;DR: In this paper, the band gaps, band structure, and excited state (exciton) energies of CdS, GaAs, and GaP semiconductor clusters are calculated using pseudopotentials.
Abstract: The band gaps, band structure, and excited‐state (exciton) energies of CdS, GaAs, and GaP semiconductor clusters are calculated using pseudopotentials. In addition, the sensitivity of the exciton energies to the size, shape, crystal structure, and lattice constant of the unit cell are investigated. The calculated exciton energies of CdS clusters are in excellent agreement with experiment over a wide range of cluster sizes. Also, the exciton states of small CdS clusters are sensitive to whether their crystal structure is zinc blende or hexagonal. Such a sensitivity is absent in large CdS clusters. Furthermore, small GaAs clusters are shown to exhibit anomalous redshift of their absorption spectra, in sharp contrast to CdS and large GaAs clusters whose spectra always shift to blue with decreasing cluster size. Finally, the lowest‐energy non‐Franck–Condon transition in GaP clusters always shifts to blue with decreasing cluster size, whereas the higher‐energy Franck–Condon transition in small clusters exhibits the anomalous redshift. These novel findings reveal that (1) the optical spectroscopy of semiconductor clusters is strongly material and crystal structure dependent; (2) the spectroscopy of small clusters is dramatically different from those of large clusters and bulk; and (3) these effects cannot be explained, even qualitatively, using the effective‐mass approximation.
TL;DR: In this article, the bulk properties of cubic GaN/GaAs were investigated by cathodoluminescence, which revealed a broad midgap peak as well as several sharp emission peaks just below the expected band gap.
Abstract: We present the first comprehensive investigation of the bulk properties, both optical and structural, of cubic GaN as grown by plasma‐assisted molecular‐beam epitaxy on vicinal (100) GaAs substrates. X‐ray measurements determined the crystal structure of GaN/GaAs to be cubic with a lattice constant of 4.5 A. High resolution transmission electron microscopy revealed a high density of planar defects propagating along the GaN {111} planes. The majority of the defects originated from disordered regions at the GaN/GaAs interface. The optical properties of the films were investigated by cathodoluminescence which revealed a broad midgap peak as well as several sharp emission peaks just below the expected band gap. The data imply that the room temperature band gap of cubic GaN is approximately 3.45 eV.
TL;DR: The luminescence from excitons confined in fully strained SiGe quantum wells is reported, and quantum-confinement effects shift the observed free-exciton edge above the bulk strained band-gap energy.
Abstract: We report the first well-resolved band-edge luminescence from excitons confined in fully strained SiGe quantum wells grown on Si. At liquid-He temperatures the photoluminescence is due to shallow bound excitons, and in addition to a no-phonon line, phonon-assisted transitions involving TA phonons and Si-Si, Si-Ge, and Ge-Ge TO phonons are observed At higher temperatures the spectra are dominated by free-exciton luminescence. Quantum-confinement effects shift the observed free-exciton edge above the bulk strained band-gap energy, and also influence the relative intensities of the three TO-phonon replicas.
TL;DR: In this paper, the valence band density of electron states shows a lone pair band and a deeper bonding band as usual, impurities have a greater effect in the nitride than in conventional lone pair semiconductors.
Abstract: Silicon Nitride is found to have a valence band maximum of nitrogen lone pair p electrons because of the planar nitrogen site. This contrasts with the usual lone pair semiconductors, such as SiO2, caused by a p4 valence configuration. Consequently although the valence band density of electron states shows a lone pair band and a deeper bonding band as usual, impurities have a greater effect in the nitride than in conventional lone pair semiconductors. Hole transport is also discussed.
TL;DR: In this article, it was found that cubic GaN grows on GaAs (001) surfaces epitaxially, while hexagonal GaN growing on GaA (111) surfaces, from the analyses of x-ray diffraction and reflection high-energy electron diffraction patterns.
Abstract: GaN epilayers were grown on GaAs substrates by gas‐source molecular‐beam‐epitaxy technique using dimethylhydrazine as a nitrogen source. It was found that cubic GaN grows on GaAs (001) surfaces epitaxially, while hexagonal GaN grows on GaAs (111) surfaces, from the analyses of x‐ray diffraction and reflection high‐energy electron diffraction patterns. Cathodoluminescence measurements suggested that the band‐gap energy of cubic GaN is around 0.37 eV larger than that of hexagonal GaN.
TL;DR: In this article, empirical expressions for both the band gap and the intrinsic carrier concentration as a function of alloy composition x and temperature are proposed for GaxIn1−xAs, and the calculated results for band gap are in close agreement with available data, while the same for intrinsic concentration give fair agreement with the data at the two ends of the alloy composition.
Abstract: The band gap and the intrinsic carrier concentration in a semiconductor are important material parameters needed in the interpretation of various experimental and theoretical data. In the present work, empirical expressions for both the parameters as a function of alloy composition x and temperature are proposed for GaxIn1−xAs. The calculated results for band gap are in close agreement with the available data, while the same for intrinsic concentration give fair agreement with the data at the two ends of the alloy composition.
TL;DR: A model density of states (DOS) for these materials is proposed, in accordance with their well-known microstructure, and explains the essential features of the optical-absorption spectra and ESR data.
Abstract: Amorphous carbon a-C and amorphous hydrogenated carbon a-C:H films were prepared by rf sputtering of a graphite target in argon and argon-plus-hydrogen atmospheres, respectively. The optical-absorption coefficients of these films were measured by a spectrophotometer in the high-absorption range and by photothermal deflection spectroscopy in the low-absorption range. They were also studied by electron-spin-resonance (ESR) measurements. The optical-absorption spectrum is found to have a rather broad peak, in contrast to the sharp rise in absorption near the band gap observed for normal semiconductors. To explain this broad peak, a model density of states (DOS) for these materials is proposed, in accordance with their well-known microstructure. This consists of a pair of broad Gaussian-like distributions lying above and below the Fermi level and separated by about 4 eV, arising out of the \ensuremath{\pi} states of the aromatic sixfold rings that comprise the bulk of the graphitic ${\mathit{sp}}^{2}$ regions, as well as pairs of discrete levels that are about 0.6 eV apart and are produced by fivefold and sevenfold rings present in these regions. The proposed DOS explains the essential features of the optical-absorption spectra and ESR data. The validity of the concept of the optical gap for these materials is also discussed.
TL;DR: The first ellipsometric measurement of the fundamental optical constants (n,k) of C60 films on Si(100) and Au overcoated Si (100) substrates was reported in this article.
Abstract: We report the first ellipsometric measurement of the fundamental optical constants (n,k) of C60 films deposited on Si(100) and Au overcoated Si(100) substrates. We obtain a highest occupied molecular orbital‐lowest unoccupied molecular orbit (HOMO‐LUMO) gap value of 2.3 eV, slightly larger than the gap values obtained from the x‐ray photoelectron spectroscopy and electron‐energy‐loss spectroscopy experiments. The structure observed in the UV is discussed in terms of single‐electron excitations across the HOMO‐LUMO gap.
TL;DR: In this paper, the light-induced red-shift in the optical absorption edge in arsenic-chalcogen glasses is reviewed and details of the changes in the atomic structure that accompany the shift in the absorption edge are of particular importance.
Abstract: Illumination with bandgap light induces changes in physical properties of many chalcogenide semiconductors. Fundamental aspects of strike reversible photodarkening (the light-induced red-shift in the optical absorption edge) in arsenic-chalcogen glasses are critically reviewed. For understanding photodarkening at the microscopic level, details of the changes in the atomic structure that accompany the shift in the absorption edge are of particular importance. Study of the structural changes by a variety of techniques has revealed a phenomenon rich in basic physics but has not led a coherent picture of the underlying microscopic mechanism. Application of advanced experimental probes providing more detailed structural information has clarified some of the fundamental changes in the atomic structure and their relation to changes in the electronic and mechanical properties. Modifications in short-range and intermediate-range order accompany photodarkening. The changes in short-range order in the form of increased AsAs bonding are very small and probably do not play a predominant role in the changes in the electronic structure. Evidence suggests that the primary effect of the light-induced changes is the modification of intermediate-range correlations.
TL;DR: A first-principles molecular-dynamics study of pure amorphous silicon obtained by simulated quench from the melt, finding an average structural, dynamical, and electronic properties in good agreement with the available experimental data.
Abstract: We present a first-principles molecular-dynamics study of pure amorphous silicon obtained by simulated quench from the melt. A cooling rate of ${10}^{14}$ K/s is sufficient to recover a tetrahedral network starting from a well-equilibrated metallic liquid having average coordination larger than 6. Dramatic changes in physical properties are observed upon cooling. In particular, a gap forms in the electronic spectrum, indicating a metal-to-semiconductor transition. The as-quenched structure has average coordination very close to 4, but contains several coordination defects as well as a large fraction of distorted bonds. Subsequent annealing reduces the amount of strain and the number of defects present in our system. The average structural, dynamical, and electronic properties of our sample are in good agreement with the available experimental data. We report a detailed analysis of the structural relaxation processes accompanying annealing and compare our findings with recent experiments.
TL;DR: In this paper, Nitrogen-containing hydrogenated amorphous carbon (a•C:H(N)) films are grown from a dc plasma of a N2+C6H6 gas mixture.
Abstract: Nitrogen‐containing hydrogenated amorphous carbon (a‐C:H(N)) films are grown from a dc plasma of a N2+C6H6 gas mixture. By varying the N2 fraction in this mixture films with different amounts of N are produced. The actual amount of nitrogen in the a‐C:H(N) films is determined by nuclear reaction analysis and by Auger electron spectroscopy profiling. The nitrogen concentration in the films grows exponentially with nitrogen content in the gas mixture reaching concentrations as high as 10 at.% for the films grown from a N2‐rich gas mixture (N2/(N2+C6H6)=0.75). The electrical and structural properties of the N2‐doped films are studied by performing electrical conductivity, thermopower (TP), optical absorption, and electron‐paramagnetic resonance measurements. Films with low (<1 at.%) nitrogen content exhibit fairly high resistivities, have an optical gap of 1 eV, are rich with dangling bonds (5×1020 cm−3) and their thermopower is positive and in the mV/K regime, indicating conductivity in the valence band tai...
TL;DR: In this article, an indirect band gap Γv25' → Δc1 was found for the new semiconductor Si1−x−yGexCy over most compositions x and y.
Abstract: Single‐crystal alloys of diamond with Si and Ge are investigated theoretically. An indirect band gap Γv25’ → Δc1 is found for the new semiconductor Si1−x−yGexCy over most compositions x and y, with an indirect Γv25’ → Lc1 gap found for the remaining compositions. The estimated band gaps span the 0.62–5.5‐eV‐range. Predictions are made for band gap versus lattice parameter in the new alloy semiconductors Si1−xCx and Ge1−xCx.
TL;DR: In this article, the optical properties of ZnSe/Zn0.86Cd0.14Se single quantum well have been investigated under direct and indirect excitation, and the temperature dependence of photoluminescence and resonant Raman scattering are investigated.
Abstract: The optical properties of strained‐layer ZnSe/Zn0.86Cd0.14Se single quantum wells have been studied. The photoluminescence under direct and indirect excitation is investigated in detail. The temperature dependence of photoluminescence and resonant Raman scattering are investigated. Very strong 2LO‐phonon Raman scattering has been observed with Zn0.86Cd0.14Se quantum wells, where the scattered photon energy is in resonance with an exciton transition. Experimental exciton energies are compared with a finite‐square‐potential quantum‐well model including band nonparabolicity and the strain effect. Based on Hill’s theory [J. Phys. C 7, 521 (1974)] we have computed the band gap of Zn1−xCdxSe as a function of composition x.
TL;DR: In this paper, the linear optical properties of poly(2,7]-2,2'-bithiophenylylene]-4,9-diphenyl-1,6-anthrazoline were investigated.
Abstract: Poly(2,7-[2,2'-bithiophenylylene]-4,9-diphenyl-1,6-anthrazoline) and poly(2,7-[2-thienylethynyl-2-thienyl]-4,9-diphenyl-1,6-anthrazoline) were prepared. These polymers showed significant changes in electronic structures as evidenced in the linear optical properties compared to the known poly(2,7-[p,p'-biphenylyl]-4,9-diphenyl-1,6-anthrazoline). Smaller band gaps (∼2 eV) were observed for these polymers.
TL;DR: In this paper, electrical conductivity, Hall mobility, thermoelectric power and optical properties were studied for indium-doped zinc oxide films produced by the magnetron sputtering technique.
TL;DR: The cathodoluminescence wavelength imaging (CLWI) method as discussed by the authors uses a focused focused electron beam across the area under investigation to obtain a 3D image of the atomic-scale morphology of QW interfaces.
Abstract: Luminescence experiments provide a powerful and nondestructive approach to the e x s i t u investigation of semiconductorheterointerfaces which might be buried up to several μm below the surface in a given complex sample structure. Combined with the ability of taking images simply by scanning the exciting focused electron beam across the area under investigation, lateral fluctuations of electronic properties like the variation of the fundamental band gapE g (x,y) can be directly visualized by scanning cathodoluminescence(CL). The novel experimental approach, cathodoluminescence wavelength imaging (CLWI), which involves recording of a complete CLspectrum at every scanning position (x,y), yields direct 3D images of the atomic‐scale morphology of quantum wells(QWs) as sensed by the QWexciton: similar to the tip of a scanning tunneling microscope, the exciton samples the local fluctuations of QW thickness L z and transforms this structural information L z (x,y) into a spectral one, the lateral variation of band gapE g (x,y) and thus the CL emission wavelength λ(x,y). Topological maps of QW interfaces can thus be recorded at various positions and at various magnifications. The interface roughness can be investigated statistically at lateral resolution starting with the diameter of the QWexciton up to the mm regime. The same experimental principle for recording λ(x,y) and E g (x,y) maps is successfully applied for the analysis of patterned structures. In the nonlattice‐matched system GaAs on Si, the lateral strain variation causes E g (x,y) fluctuations and can thus be directly imaged by CLWI. Metalorganic chemical vapor deposition grown GaAs layers on micropatterned Si(001) substrates show strongly inhomogeneous doping with Si impurities. By means of CLWI the strong increase of this Si incorporation in the vicinity of free {111} surfaces is measured and Si concentration maps are recorded across the complete sample pattern.
TL;DR: In this paper, the direct and indirect band gaps of Si1−x−yGexSny are inferred from the calculated energy-band structure of α•Sn and from the known structures of Ge and Si.
Abstract: The direct and indirect band gaps of Si1−x−yGexSny are inferred from the calculated energy‐band structure of α‐Sn and from the known structures of Ge and Si. Our assumptions are: that the energy‐band shapes of the binaries Sn1−xGex, Ge1−ySiy and Si1−ySny change smoothly with x and y, and that the energy gap of SiGeSn can be estimated by interpolation from the gaps of SnGe, GeSi, and SiSn. The optical indices of refraction of SiGeSn are also estimated.
TL;DR: The angle-resolved-photoemission studies can provide much additional information about the electronic structure of correlated materials like NiO and the interesting angle and photon-energy dependence of the satellite emission is reported.
Abstract: We have performed angle-resolved-photoemission experiments and local-density-functional (LDA) band calculations on NiO to study correlation and band effects of this conceptually important compound. Our experimental result suggests a dual nature of the electronic structure of NiO. On the one hand, the LDA band calculation has some relevance to the electronic structure of NiO, and the inclusion of the antiferromagnetic order is essential. For the lower O 2p bands, the LDA calculation agrees almost perfectly with experimental energy positions and dispersion relations. On the other hand, discrepancies between the experiment and the LDA calculation do exist, especially for the Ni 3d bands and the O 2p bands that are heavily mixed with the Ni 3d bands. It appears that the main discrepancies between the experimental results and the LDA calculation are concentrated in the regions of the insulating gap and the valence-band satellite. In addition to these results, we also report the interesting angle and photon-energy dependence of the satellite emission. The above results show that the angle-resolved-photoemission studies can provide much additional information about the electronic structure of correlated materials like NiO.
TL;DR: An electroactive polymer with a lowered band gap was obtained from the monomer cyclopenta[2,1-b;3,4-b′]dithiophen-4-one as discussed by the authors.
Abstract: An electroactive polymer with a lowered band gap has been obtained from the monomer cyclopenta[2,1-b;3,4-b′]dithiophen-4-one.