Showing papers on "Electronic band structure published in 1975"
TL;DR: A detailed study of the generalized susceptibility of Sc metal determined from an accurate augmented-plane-wave method calculation of its energy-band structure is presented in this article, which yields simple analytic expressions for the integral inside a tetrahedral microzone of the Brillouin zone which depends only on the volume of the tetrahedron and the differences of the energies at its corners.
Abstract: A detailed study of the generalized susceptibility $\ensuremath{\chi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ of Sc metal determined from an accurate augmented-plane-wave method calculation of its energy-band structure is presented. The calculations were done by means of a computational scheme for $\ensuremath{\chi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ derived as an extension of the work of Jepsen and Andersen and Lehmann and Taut on the density-of-states problem. The procedure yields simple analytic expressions for the $\ensuremath{\chi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ integral inside a tetrahedral microzone of the Brillouin zone which depends only on the volume of the tetrahedron and the differences of the energies at its corners. Constant-matrix-element results have been obtained for Sc which show very good agreement with the results of Liu, Gupta, and Sinha (but with one less peak) and exhibit a first maximum in $\ensuremath{\chi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ at $(0, 0, 0.31)\frac{2\ensuremath{\pi}}{c}$ [vs $(0, 0, 0.35)\frac{2\ensuremath{\pi}}{c}$ obtained by Liu et al.] which relates very well to dilute rare-earth alloy magnetic ordering at ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}}_{m}=(0, 0, 0.28)\frac{2\ensuremath{\pi}}{c}$ and to the kink in the LA-phonon dispersion curve at $(0, 0, 0.27)\frac{2\ensuremath{\pi}}{c}$.
319 citations
269 citations
TL;DR: In this article, the electronic structures of the hcp transition metals, Zr, Hf, Ru, and Os were calculated using the linear muffin-tin-orbital method described in the previous paper.
Abstract: Using the linear muffin-tin-orbital method described in the previous paper, (Phys. Rev. B 12: 3060) the electronic structures of the hcp transition metals, Zr, Hf, Ru, and Os were calculated . It is shown how the band structures of these metals may be synthesized from the sp and d bands, and the effects of hybridization, relativistic band shifts and spin--orbit coupling are illustrated by the example of Os. By making use of parameters derived from the muffin-tin potential, trends in the positions and widths of the energy bands, especially the d bands, are discussed as a function of the location in the periodic table. The densities of states of the four metals are presented and the calculated heat capacities compared with experiment. The Fermi surfaces of both Ru and Os are found to be in excellent quantitative agreement with de Haas--van Alphen measurements, indicating that the calculated d-band position is misplaced by less than 10 mRy. Very small pieces of Fermi surface, which have not yet been observed experimentally, are predicted for Os. The limited amount of experimental information available for Zr can be fairly satisfactorily interpreted if the calculated d bands, are raised by about 10--20 mRy relative tomore » the sp bands. This gives rise to a Fermi surface which is topologically equivalent to that recently found in Ti, and which does not support open orbits when the magmetic field is sufficiently great that breakdown is complete. It is suggested that the Fermi surface of Hf is probably similar, although very little experimental evidence is available for this metal. Some comments are made about the calculational method, which has proved to be physically transparent, accurate and extremely fast, and the adequancy of the standard potential, which has now been successfully employed in calculations on the great majority of the transition metals. (auth)« less
191 citations
TL;DR: In this paper, the position of the charge transfer band of Eu3+ in the absorption spectra of a number of oxides is discussed and it is shown that this position is more or less fixed in octahedral VI coordination and that it varies in VIII and XII coordinations as a function of the effective ionic radius of the relevant host lattice ion.
190 citations
TL;DR: In this article, the temperature dependence in the range 77-400 K of the carrier concentration, resistivity and mobility of a series of n and p-type single crystal, liquid-phase epitaxial layers of Ga1−xAlxAs are presented.
Abstract: The temperature dependence in the range 77–400 K of the carrier concentration, resistivity and mobility of a series of n and p-type single crystal, liquid-phase epitaxial layers of Ga1−xAlxAs are presented. These layers were doped, n-type with tellurium, and p-type with germanium to yield carrier concentrations in the range 1017 – 1018cm−3 at 295 K. Donor and acceptor ionization energies, eD and eA, are derived from the data. The dependence of eD on alloy composition is interpreted in terms of the known band structure variation in the alloy system.
122 citations
TL;DR: In this paper, the electron tunneling spectra of Pb, Mg, Au, and Ag were studied and the effect on the electronic standing-wave energies was measured.
Abstract: Periodic structure in the electron tunneling spectra of Pb, Mg, Au, and Ag has been observed. Such spectra represent in fact a direct observation of size-dependent electronic states in thin metal films. Films with thicknesses from 100 to 1000 \AA{} were studied and the effect on the electronic standing-wave energies was measured. The physical model for these effects and their observability involve the existence of so-called commensurate states. The spacing of the quantized energy levels provides a direct measurement of the electron group velocity while their location in energy determines the position of band edges and other critical energy states in the band structure of the metals. In some cases, the effective mass can also be determined. A qualitative theoretical picture is sufficient to understand all of the sailient features of the observations. A number of experiments including alloying, strain, and electric field modulation are also described.
121 citations
TL;DR: In this paper, photoelectron energy spectra have been measured on the layer compounds $1T$-Ta${\mathrm{Se}}_{2}, $ 1T$ -Ta$
Abstract: Photoelectron energy spectra have been measured on the layer compounds $1T$-Ta${\mathrm{Se}}_{2}$, $1T$-Ta${\mathrm{S}}_{2}$, and $2H$-Ta${\mathrm{Se}}_{2}$ as a function of both polar and azimuthal angle of emission. Light was incident normally upon the sample and the photon energy in most of the experiments was 10.2 eV. The measurements were performed in a specially constructed ultrahigh vacuum chamber using a movable retarding potential-energy analyzer. The variations with polar angle of the positions of peaks in the spectra have been used to plot experimental energy bands which are found to compare favorably with the first-principles calculations of Mattheiss. The azimuthal dependence of the photoemission, and in particular the Ta $d$-emission intensity, was found to display strong anisotropies. X-ray orientation of the $1T$ samples revealed that if one assumes that the Ta $d$ photoelectrons originate on Ta atoms, then they propagate preferentially along directions which avoid neighboring chalcogen atoms. The relationship with atomic orbitals and band theory is discussed. In the hexagonal crystal $2H$-Ta${\mathrm{Se}}_{2}$, residual threefold rotational symmetry is observed in the Ta $d$ emission and is attributed to the shortness of the photoelectron escape depth.
120 citations
TL;DR: In this paper, the authors derived approximate partial densities of valence states for AgCl and AgBr for photon energies of 16.8, 21.2,,26.9, 40.8 and 1486.6$ eV.
Abstract: AgCl and AgBr have been investigated by photoemission for photon energies $h\ensuremath{
u}=16.8, 21.2, ,26.9, 40.8, \mathrm{and} 1486.6$ eV. By exploiting the strong dependence on $h\ensuremath{
u}$ of the photoionization cross sections for the atomic orbitals composing the valence bands, we have been able to deduce approximate partial $p$ and $d$ densities of valence states for these compounds. The most conspicuous feature of the photoelectron distribution curves is a sharp peak near the center of the valence band, which our partial density of states shows to be mostly $d$-like. The $p$ density of states exibits two main peaks centered at 2- and 5-eV binding energy and a gap at the energy of the sharp $d$ peak. From the $p$ and $d$ densities of states we conclude that, except for the sharp $d$-like peak and the associated $p$ gap, the $p$ and $d$ functions are nearly equally and uniformly mixed throughout the valence band. The results are compared with partial densities of states calculated with a simplified tight-binding scheme and the band structure is discussed in detail.
100 citations
TL;DR: A review of XPS and AES studies performed on clean transition metal oxide (TMO) surfaces is presented in this article, where the main aspects of these spectra and the difficulties encountered in their interpretation are given.
90 citations
TL;DR: In this paper, room-temperature electrical resistivity and Hall effect measurements as a function of pressure are reported on p-type MoS2 and on n-type MOS2, MoSe2 and MoTe2.
Abstract: Room-temperature electrical resistivity and Hall effect measurements as a function of pressure are reported on p-type MoS2 and on n-type MoS2, MoSe2 and MoTe2. In each case, the resistivity decreases under pressure, due to an increase in the carrier concentration. The Hall mobility is relatively pressure-independent. The data are consistent with the predominance of extrinsic conduction in these semiconductors until well above room temperature. The impurity activation energy and its pressure dependence are given, together with estimates of the intrinsic indirect bandgap obtained from high temperature conductivity measurements, photoemission studies and band structure calculations.
83 citations
TL;DR: In this paper, the optical constants n and k have been determined over the wavelength range from 2000-250 nm by measurements of reflectance and transmittance at normal incidence and treating these data by the method of Denton et al. (1972).
Abstract: The optical constants n and k have been determined over the wavelength range from 2000-250 nm by measurements of reflectance and transmittance at normal incidence and treating these data by the method of Denton et al. (1972). The effects of surface roughness have been taken into account. Analysis of the dependence of absorption on photon energy have shown that the experimental results may be explained by the occurrence of direct transitions from 2.42 eV to 2.82 eV, in the case of CdS, followed by combined direct and indirect transitions beyond 2.82 eV assuming the energy band to be parabolic, or equally well by assuming only direct transitions between nonparabolic bands. The results for ZnS films are similar and may be treated in the same way. It is concluded that these materials both show absorption by direct transitions just beyond the absorption edge, and that at higher energies the form of the absorption curve is probably due to the combined effects of indirect transitions together with direct transitions between nonparabolic bands.
TL;DR: In this article, the semiconductor-metal transition in VO2 has been investigated by means of XPS measurements, and the band gap in the semiconducting region is found to be temperature-dependent with a room temperature value of Eg=0.3 eV, in agreement with resistivity measurements.
Abstract: The semiconductor-metal transition in VO2 has been investigated by means of XPS measurements. The band gap in the semiconducting region is found to be temperature-dependent with a room temperature value of Eg=0.3 eV, in agreement with resistivity measurements. The core lines, which are asymmetric below Tnu broaden and become symmetric above Tt. A model is discussed to explain the broadening in the metallic region, which requires that the core hole-valence electron interaction is comparable to the bandwidth. The relative shift of the O 1s and V 2p peak positions below and above Tt indicates that the charges on the ions are highest in the metallic phase, suggesting a more ionic bond in this region.
TL;DR: In this paper, a small periodic cluster approach was used to solve the electronic eigenvalue problem of hexagonal boron nitride and showed that the defect level 1.1-1.4 eV is characterized by a three-boron character.
Abstract: Substitutional and displaced carbon impurities and an isolated nitrogen vacancy in hexagonal boron nitride are theoretically investigated by the "small periodic cluster" approach. The perfect-solid band structure is calculated from the solution of the eigenvalues of a finite and periodic cluster of atoms arranged according to the known crystal structure. The linear combination of atomic orbitals representation of the crystal orbitals is adopted and semiempirical MO (molecular orbital) methods (extended Huckel, iterative extended Huckel) are used for the solution of the electronic eigenvalue problem. Point-defect problems are then treated by introducing the impurity atom or the vacant site into the otherwise perfect periodic cluster, and repeating the solution. Lattice relaxations are introduced around the defect site and charge redistribution among the cluster atoms is allowed for via self-consistent MO treatment. For a substitutional carbon impurity defect, it is observed that two deep defect levels, mainly localized on the carbon atom, appear (3.2-4.9 eV below the conduction band). Another level splits from the conduction band as the carbon atom is raised from the layer plane in a perpendicular direction. This level, 1.0-1.3 eV below the conduction band, has a symmetrical charge distribution on the three boron atoms surrounding the impurity site. As the distance of the carbon atom from the layer plane is increased to infinity, a nitrogen vacancy is formed. It is characterized by a defect level 1.1-1.4 eV apart from the conduction-band edge which also possesses a three-boron character. Lattice relaxations were shown to stabilize these defects. The findings agree semiquantitatively with the experimental results on these defects.
TL;DR: In this paper, an experimental study of the photoelectric yield of doped solid rare gases in the extreme ultraviolet (h/ω = 8−30 eV) spanning the range of impurity excitations, exciton states, and interband transitions was performed.
Abstract: In this paper we report the results of an experimental study of the photoelectric yield of doped solid rare gases in the extreme ultraviolet (h/ω = 8−30 eV) spanning the range of impurity excitations, exciton states, and interband transitions. Results were obtained for Xe in Kr, Xe in Ar, Kr in Ar, and benzene in Ar, Kr, and Xe. For dilute atomic and molecular impurities in solid rare gases three intrinsic photoemission mechanisms are exhibited: (a) direct excitation from the impurity state above the impurity threshold, (b) electronic energy transfer from the host exciton states to the impurity states resulting in exciton induced impurity photoemission, and (c) direct photoemission from the host matrix at energies above the matrix threshold. The photoemission thresholds from impurity states via processes (a) or (b) result in detailed information regarding electron affinities of solid rare gases which are in good agreement with recent data for the pure solids. A detailed study of exciton induced photoemiss...
TL;DR: In this article, a theory of the band structure of semiconductor superlattices has been developed for both the direct-bandgap and indirect-band-gap barrier layers taking into account the multivalley and nonparabolic band structure.
Abstract: A theory of the band structure of semiconductor superlattices has been developed for both the direct-band-gap and indirect-band-gap barrier layers taking into account the multivalley and nonparabolic band structure of the materials forming the superlattice. For direct-band-gap barrier layers the nonparabolicity in the band structure may alter the electronic energy levels measured from the bottom of the potential wells by as much as 26%. On the other hand for indirect-band-gap barrier layers the alteration due to the nonparabolicity is about 14%. It is also found that even for indirect-band-gap barrier layers the band structure is mainly determined by the states corresponding to the direct-gap minimum. Energy levels calculated on the basis of the theory presented are also found to agree with those obtained in recent experiments with double-barrier heterostructures.
TL;DR: In this paper, the authors reported two sets of differential reflectivity measurements (electroreflectivity and piezoreflectivity) performed on GaAs under high-resolution conditions.
Abstract: Recent measurements of the lasing energy as a function of temperature in high‐purity GaAs lasers have attempted to investigate the relation between this energy and the one‐electron band gap. Because of a lack of precision in the position of the band gap at high temperature, these measurements show strongly conflicting results. In this work, we report two sets of differential reflectivity measurements (electroreflectivity and piezoreflectivity) performed on GaAs under high‐resolution conditions. Both series of results give for the excitonic absorption edge at room temperature a value E0=1.424±0.002 eV which is about 20 meV higher than the lasing energy reported for the highest‐purity GaAs samples. This result confirms that the lasing energy in GaAs is well below the one electron band gap. In addition, we show that this energy separation is an increasing function of temperature. Finally we discuss a simple model of band‐to‐band recombination including electron‐electron interaction effects and we show that i...
TL;DR: In this paper, the transport properties of electrons in energy band tails of disordered semiconductors are studied experimentally using a material system in which the width and shape of the band-tail are approximately known and the Fermi energy is controllable.
Abstract: Transport properties of electrons in energy band tails of disordered semiconductors are studied experimentally using a material system in which (i) the width and shape of the band-tail are approximately known and (ii) the Fermi energy is controllable. The material is heavily-doped, closely-compensated, crystalline n-GaAs whose compensation ratio can be made arbitrarily close to unity by the use of two techniques that are described in detail. This control of the Fermi level through compensation permits the measurement of the transport properties of electrons at various energies in the band-tail. Using band tails having a width of ∼50 meV, measurements have been made of the temperature dependence of the d.c. conductivity and Hall coefficient, the frequency dependence of the a.c. conductivity and the electric field dependence of the d.c. conductivity (the last two at low temperatures). The evidence demonstrates the progressively greater localization of states deeper in the tails. No sign is found of...
TL;DR: In this article, a highly crystalline polymer is described in which all the polymer chains are parallel and the backbone of the chains is conjugated, and it is postulated that the low-lying (<5 eV) electronic excitations are electrons and holes in one-dimensional bands confined to individual chains.
Abstract: A highly crystalline polymer is described in which all the polymer chains are parallel and the backbone of the chains is conjugated. It is postulated that the low-lying (<5 eV) electronic excitations are electrons and holes in one-dimensional bands confined to individual chains. The band structure is deduced. The crystal is a semiconductor, EG approximately=2 eV, for charge transfer along the chain direction and an insulator in perpendicular directions. Singular Van Hove optical transitions characteristic of one dimension are discussed and shown to lead to peaks in the reflectivity. The optical and Raman properties of the model are compared with experimental results.
TL;DR: A first-principles computation of the band structure of ferromagnetic hcp cobalt is reported in this paper, where a muffin-tin potential and a Kohn-Sham exhange-correlation potential were used in conjunction with a rigid exchange splitting.
Abstract: A Korringa-Kohn-Rostoker first-principles computation of the band structure of ferromagnetic hcp cobalt is reported A muffin-tin potential and a Kohn-Sham exhange-correlation potential were used in conjunction with a rigid exchange splitting Twelve energy bands in $\frac{1}{24\mathrm{th}}$ of the hcp Brillouin zone were calculated as well as the density of states and the Fermi surface The exchange splitting was found to be 139 eV and a total density of states at the Fermi level of 1561 electrons/(atom Ry) The spin-orbit coupling constant ${\ensuremath{\xi}}_{3d}$ has been computed and is equal to 6 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ Ry The essential features of the band structure agreed with the requirements of the itinerant-electron model of ferromagnetism of the Stoner-Wohlfarth theory Our resulting density of states was able to explain the available photoemission data The calculated Fermi surface is in good agreement with the de Haas-van Alphen experiments, particularly for the neck of the point $\ensuremath{\Gamma}$ in the spin-up Fermi surface The spin-orbit interaction has been taken into account in a qualitative way in order to explain the orbits around $L$ in the spin-down Fermi surface A comparison with the existing experimental data has permitted us to estimate the mass enhancement due to many-body effects at the $\ensuremath{\Gamma}$ neck as 104, resulting in a value of 081 for the electron-magnon contribution
TL;DR: In this article, the conductivity of (SN)/sub x/ does not undergo a Peirels Frohlich transition, but increases with decreasing temperature, and alternative hypotheses to account for this anomaly are described, and calculations of the orthogonalized plane wave band structure, and one-electron state densities carried out in order to test these hypotheses.
Abstract: The conductivity of (SN)/sub x/ does not undergo a Peirels Frohlich transition, but increases with decreasing temperature. Alternative hypotheses to account for this anomaly are described, and calculations of the orthogonalized plane wave band structure, and one-electron state densities carried out in order to test these hypotheses. The low temperature conductivity is believed to be due to closed Fermi surfaces produced by electronic coupling between chains. The orthogonalized plane wave structure is compared with the Lyon and Penn crystal structures, but no definite conclusion reached. 24 references.
IBM1
TL;DR: In this paper, the position of energy bands at symmetry points for both filled and empty bands within 1 Ry of the gap was determined using anisotropic direct transition model of photoemission applicable to cleaved singlecrystal semiconductors.
Abstract: We analyze photoemission spectra for Ge obtained for photon energies $6.5\ensuremath{\le}h\ensuremath{
u}\ensuremath{\le}25$ eV and determine the position of energy bands at symmetry points for both filled and empty bands within 1 Ry of the gap. This experimental band structure is obtained using a recently developed anisotropic direct-transition model of photoemission applicable to cleaved single-crystal semiconductors. For the band-structure determination we also employ a direct transition analysis of optical spectra obtained by others. We fit nonlocal-pseudopotential calculations to the experimentally-determined band positions, and thereby determine the importance of both energy and $l=2$, angular momentum nonlocality in the pseudopotential. Our results for the position of highlying conduction-band states suggest 0 to + 10% self-energy (exchange-correlation) corrections to the energy of electrons excited into the conduction bands. Energy bands which provide a good fit to the experimental band positions are used, along with pseudo-wave-function matrix elements, to calculate various physical properties (photoemission spectra, optical-response functions, and one-electron state densities), and the results of these calculations are compared with experiment. The quality of the fits obtained indicates that the electronic excited-state (and ground-state) properties of Ge for excitations far from the gap are described well by a one-electron model.
TL;DR: In this paper, the existence of field-induced gaps is predicted and applications to model systems such as the Kronig-Penney model are presented, showing that the effect is large and should be readily observable with currently available laser sources.
Abstract: The nonlinear interaction of laser radiation with crystalline solids results in a modified band structure which is a natural extension of the usual Bloch picture. A theoretical discussion is presented in which the existence of field-induced gaps is predicted. Applications to model systems such as the Kronig-Penney model are presented. Examination of realistic systems such as the narrow band gap semiconductors suggest that the effect is large and should be readily observable with currently available laser sources.
TL;DR: In this article, a simple k · p theory based on Si and the ionic X gap is applied to the conduction band of GaP and it is found that recent evidence may indicate a location of the absolute minima away from the zone boundary.
TL;DR: In this article, energy band structure calculations are carried out on three tetragonal dioxides belonging to the IV group (SnO2, GeO2 and β-PbO2) with the help of the KKR method, and the results obtained are compared with many experimental results in order to try to make a synthesis of the optical properties of these compounds and to relate them to theoretical results.
TL;DR: In this article, an analysis of low-energy-electron-diffraction intensity profiles from the clean (111) face of platinum was carried out, based on a $T$-matrix multiple-scattering theory with corrections for lattice vibrations.
Abstract: An analysis of low-energy-electron-diffraction intensity profiles from the clean (111) face of platinum is carried out. Calculated intensities are compared with experimental results for specular and nonspecular beams at several angles of incidence for electron energies \ensuremath{\le}100 eV. The calculations are based on a $T$-matrix multiple-scattering theory with corrections for lattice vibrations. The scattering from a single atomic site is modeled with a conventional band-structure potential parametrized by six partial-wave phase shifts. The constant inner potential ${V}_{0}$ determined from addition of the Fermi energy and a measured value of the work function is found to predict the peak positions accurately. The calculations adequately describe the shapes and relative intensities of primary and secondary features in the experimental intensity profiles. Analysis of the data indicates that the spacing of the topmost atomic layer is the same as the bulk value to within 5% (or approximately 0.1 \AA{}).
TL;DR: In this article, a general method to study the band structure of compositionally disordered semiconductors is proposed, where the effects of chemical disorder are added to the virtual-crystal band structure using the pseudopotential method and second order perturbation theory.
TL;DR: In this article, the electronic structure of excitonic molecule is discussed by taking into account the detailed band structure of CuCl, CuBr, CdS, cdSe and ZnO.
Abstract: The electronic structure of excitonic molecule is discussed by taking into account the detailed band structure of CuCl, CuBr, CdS, CdSe and ZnO. Especially the excitonic molecule in CuBr is interesting due to the less simple valence band. The fine structure of the excitonic molecule is clarified under the effective electron-hole exchange effect and the interband hole-hole scattering beyond the effective mass approximation.