Showing papers on "Band gap published in 1984"
TL;DR: In this paper, the Schottky barrier heights for metal-semiconductor interfaces with a variety of metals have been calculated, and they are in excellent agreement with experiment for interfaces with various metals.
Abstract: Simple physical considerations of local charge neutrality suggest that near a metal-semiconductor interface, the Fermi level in the semiconductor is pinned near an effective gap center, which is simply related to the bulk semiconductor band structure. In this way “canonical” Schottky barrier heights are calculated for several semiconductors. These are in excellent agreement with experiment for interfaces with a variety of metals.
1,121 citations
PARC1
TL;DR: In this paper, the authors compared the band gap between band-and cluster-theory predictions on a cleaved NiO single crystal and showed that a large Coulomb interaction alone does not prevent NiO from being a metal.
Abstract: Photoemission and bremsstrahlung-isochromat-spectroscopy data on a cleaved NiO single crystal are presented and compared to band- and cluster-theory predictions. In contrast to band-theory predictions the band gap is found to be large but not determined solely by the even larger $d\ensuremath{-}d$ Coulomb interactions so that NiO is not a Mott-Hubbard insulator in the simplest sense. A large $d\ensuremath{-}d$ interaction need not prevent NiS from being a metal.
703 citations
TL;DR: In this article, the development of bulk optical properties as a function of crystallite size for the inorganic direct gap semiconductor CdS was studied in situ at extreme dilution.
Abstract: This paper reports experimental studies of the development of bulk optical properties as a function of crystallite size for the inorganic direct gap semiconductor CdS. Small crystallites are synthesized via colloidal chemical techniques, and their optical properties are studied in situ at extreme dilution. The crystallites are characterized via high resolution transmission electron microscopy. Direct images show (111) lattice planes, and establish the crystallite structures as close to those of excised fragments of bulk CdS (zinc‐blende cubic). Large crystallites (> 100 A average diameter) show an optical absorption, in colloidal solution, close to that of bulk crystalline material. However, small crystallites of 30 A average diameter show a large blue shift (∼0.8 eV) in absorption edge (effective band gap), and an intensification of edge absorption relative to absorption at higher energy regions. These observations can be understood as quantum size effects resulting from confinement of an electron and hole in a small volume. 40 A average size crystallites show a smaller shift (∼0.25 eV), and corresponding changes in their fluorescence, and resonance Raman excitation, spectra.
636 citations
TL;DR: In this article, the optical properties of evaporated films of doped semiconducting In2O3 in the 2-6eV range were investigated, i.e., around the fundamental bandgap.
Abstract: In this paper we investigate the optical properties of evaporated films of doped semiconducting In2O3 in the 2-6-eV range, i.e., around the fundamental bandgap. The study serves two main purposes: to elucidate basic properties of a heavily n-doped semiconductor, and to improve our understanding of a technologically important material which is widely used when transmittance of visible or solar radiation needs to be combined with good electrical conduction or low thermal emittance.
552 citations
TL;DR: In this paper, the ferrimagnetic Fe 3 O 4 was calculated in the high temperature cubic phase by means of self-consistent APW method and it was shown that the itinerant electron model is more adequate than the localized electron model.
Abstract: Band structure of the ferrimagnetic Fe 3 O 4 was calculated in the high temperature cubic phase by means of self-consistent APW method. Though the obtained band structure corresponds closely with the ionic Neel model, it was shown that the itinerant electron model is more adequate than the localized electron model. The minority spin d e bands of B site iron have an electron Fermi surface at the \( \varGamma \) point and hole surfaces around the W point. Experimental data including photoelectron emission, optical reflectivity, neutron scattering and transport phenomena were discussed qualitatively in relation to the calculated band structure.
445 citations
TL;DR: In this paper, the occupied and empty electronic states of the insulator Ce${\mathrm{O}}_{2}$ have been studied by high-energy spectroscopies.
Abstract: The occupied and empty electronic states of the insulator Ce${\mathrm{O}}_{2}$ have been studied by high-energy spectroscopies. The outer-level spectra reveal empty localized $4{f}^{1}$ states within the band gap. The core-level spectra display different final-state populations of the $4f$ localized states which are well predicted by a many-body calculation taking into account the presence of $f$-symmetry admixture in the valence band. A mixed valence can be definitely excluded in Ce${\mathrm{O}}_{2}$.
419 citations
TL;DR: In this article, the authors developed a new theory to describe the characteristics of amorphous silicon based alloy field effect transistors and showed that the transition from below to above threshold operation occurs when the Fermi level in the accumulation region moves from the deep to tail localized states in the energy gap.
Abstract: In this paper we develop a new theory to describe the characteristics of amorphous silicon based alloy field‐effect transistors. We show that the transition from below to above threshold operation occurs when the Fermi level in the accumulation region moves from the deep to tail localized states in the energy gap. The current‐voltage and capacitance‐voltage characteristics are related to the basic material parameters such as the distribution of localized states in the energy gap, band mobility, device geometry, channel doping, and series resistances. Our analysis shows that an on current in excess of 2×10−7 A/μm gate width can be obtained with a 10‐μm gate length. We also demonstrate that even in the above threshold regime the field‐effect mobility is dependent on the gate voltage. Our theory can be used to optimize the design of amorphous silicon based alloy field‐effect transistors.
393 citations
TL;DR: Energy distribution of Pb centers (⋅Si≡Si3) and electronic traps (Dit) at the Si/SiO2 interface in metal-oxide-silicon (MOS) structures was examined by electric-field-controlled electron paramagnetic resonance (EPR) and capacitancevoltage (C‐V) analysis on the same samples.
Abstract: Energy distribution of Pb centers (⋅Si≡Si3) and electronic traps (Dit) at the Si/SiO2 interface in metal‐oxide‐silicon (MOS) structures was examined by electric‐field‐controlled electron paramagnetic resonance (EPR) and capacitance‐voltage (C‐V) analysis on the same samples Chips of (111)‐oriented silicon were dry‐oxidized for maximum Pb and trap density, and metallized with a large MOS capacitor for EPR and adjacent small dots for C‐V measurements Analysis of C‐V data shows two Dit peaks of amplitude 2×1013 eV−1 cm−2 at Ev+026 eV and Ev+084 eV The EPR spin density reflects addition or subtraction of an electron from the singly occupied paramagnetic state and shows transitions of amplitude 15×1013 eV−1 cm−2 at Ev+031 eV and Ev+080 eV This correlation of electrical and EPR responses and their identical chemical and physical behavior are strong evidence that ⋅Si≡Si3 is a major source of interface electronic traps in the 015–095 eV region of the Si band gap in unpassivated material
333 citations
Abstract: The photophysical and photochemical properties of the series of tris-chelate complexes Ru(bpy)/sub n/(bpyz)/sub 3-n//sup 2 +/, Ru(bpy)/sub n/(bpym)/sub 3-n//sup 2 +/, Ru(bpym)/sub n/(bpyz)/sub 3-n//sup 2 +/, and Ru(bpy)(bpym)(bpyz)/sup 2 +/ (n = 0, 1, 2, 3; bpy = 2,2'-bipyridine, bpyz = 2,2'-bipyrazine, bpym = 2,2'-bipyrimidine) are described. From the results of temperature-dependent lifetime (210-345 K) and room-temperature emission quantum yield measurements have been obtained: (1) k/sub r/ and k/sub nr/, the radiative and nonradiative decay rate constants for the emitting MLCT manifold and (2) kinetic parameters which suggest the intervention of additional excited states. The significant points of the study are the following: (1) trends in k/sub nr/ properties are understandable based on the energy gap law, (2) low-lying dd states strongly influence lifetimes and photochemical instabilities for the complexes Ru(bpyz)/sub 3//sup 2 +/, Ru(bpym)/sub 3//sup 2 +/, Ru(bpy)(bpyz)/sub 2//sup 2 +/, Ru(bpy)(bpym)/sub 2//sup 2 +/, Ru(bpym)(bpyz)/sub 2//sup 2 +/, Ru(bpym)/sub 2/(bpyz)/sup 2 +/, and Ru(bpy)(bpym)(bpyz)/sup 2 +/ at room temperature, and (3) for the complexes Ru(bpy)/sub 2/(bpyz)/sup 2 +/ and Ru (bpy)/sub 2/(bpym)/sup 2 +/ there is no evidence for low-lying dd states and these and/or related mixed-ligand complexes may provide a basis for a new series of photochemicallymore » stable Ru-polypyridyl chromophores.« less
232 citations
TL;DR: In this paper, the Gibbs free energy efficiency of hydrogen-evolving photoelectrochemical cells with semiconductor electrodes was shown to exceed the solar-to-fuel conversion efficiency of green plants.
Abstract: Sunlight is directly converted to chemical energy in hydrogen-evolving photoelectrochemical cells with semiconductor electrodes. Their Gibbs free energy efficiency of solar-to-hydrogen conversion, 13.3 percent, exceeds the solar-to-fuel conversion efficiency of green plants and approaches the solar-to-electrical conversion efficiency of the best p-n junction cells. In hydrogen-evolving photoelectrodes, electron-hole pairs photogenerated in the semiconductor are separated at electrical microcontacts between the semiconductor and group VIII metal catalyst islands. Conversion is efficient when the island diameters are small relative to the wave-lengths of sunlight exciting the semiconductor; when the island spacings are smaller than the diffusion length of electrons at the semiconductor surface; when the height of the potential energy barriers that separate the photogenerated electrons from holes at the semiconductor surface is raised by hydrogen alloying of the islands; when radiationless recombination of electron-hole pairs at the semiconductor-solution interface between the islands is suppressed by controlling the semiconductor surface chemistry; and when the semiconductor has an appropriate band gap (1.0 to 1.8 electron volts) for efficient solar conversion.
225 citations
TL;DR: In this article, the same impurity is compared in different crystals, referring them to the vacuum level through the use of the photothreshold reveals a remarkable material invariance of the levels in III-V and II-VI semiconductors.
Abstract: Whereas the conventional practice of referring binding energies of deep donors and acceptors to the band edges of the host semiconductor does not produce transparent chemical trends when the same impurity is compared in different crystals, referring them to the vacuum level through the use of the photothreshold reveals a remarkable material invariance of the levels in III-V and II-VI semiconductors. It is shown that this is a consequence of the antibonding nature of the deep gap level with respect to the impurity atom-host orbital combinations.
TL;DR: A detailed description of the methods available for a derivation of a band structure from angle resolved photoemission spectra is given using copper as an example in this article, where data from various sources are collected and reviewed critically in order to derive an experimental band structure for copper.
TL;DR: In this paper, the authors proposed InAsSb strained layer superlattices (SLSs) as novel III-V semiconductor materials with the potential for long wavelength intrinsic detector applications and showed that the wavelength response of various SLSs with x ≳ 0.73 can be extended to 12 μm at 77 K through the intentional use of layer strains.
Abstract: InAsSb strained‐layer superlattices (SLS’s) are proposed as novel III–V semiconductor materials with the potential for long wavelength intrinsic detector applications. Theoretical studies of the band gaps of various InAs0.4Sb0.6/InAs1−xSbx SLS’s with x > 0.6 have been carried out. The results indicate that the wavelength response of various SLS’s with x ≳ 0.73 can be extended to 12 μm at 77 K through the intentional use of layer strains. These new structures offer the metallurgical and processing advantages of III–V semiconductors for 12 μm detector applications. Further advantages include a weaker dependence of the SLS band gap on composition and reduced band‐to‐band tunneling in the SLS compared to bulk Hg0.8Cd0.2Te.
TL;DR: In this article, the luminescence properties of the bismuth compounds Bi2Ge3O9, Bi12MO20, Bi2Al4O9 and PbM2O4 (M = Al, Ga) are reported and discussed.
TL;DR: In this paper, it was shown that the equation ΔE = εT2/(T + β) is a second order approximation of the electron-phononon.
Abstract: It is shown that the equation ΔE = αT2/(T + β), which is commonly used to describe the temperature variation of energy gaps in semiconductors, is a second order approximation of the electron–phonon...
TL;DR: In this article, the authors measured the magnitude of conduction-band discontinuities at heterojunctions for several compositions of InGaAsP grown lattice matched on InP.
Abstract: We have measured the magnitude of the conduction‐band discontinuities at heterojunctions for several compositions of InGaAsP grown lattice matched on InP. We find that the conduction‐band discontinuity (ΔEc) is related to the difference in band gaps (ΔEg) between the InGaAsP and InP layers via ΔEc =0.39(ΔEg). Thus, 40% of the band‐gap difference lies in the conduction band of this material system. The measurements were made on a series of composition of InGaAsP spanning the alloy range from In0.53Ga0.47As (with energy gap Eg =0.75 eV) to InP (Eg =1.35 eV) using capacitance‐voltage techniques. Depletion deep into the semiconductor layers was facilitated by the formation of organic‐on‐inorganic semiconductor contact barriers on the InGaAsP surface.
TL;DR: In this paper, a p-type semiconductor with an average hole mobility of 1.1 × 10 −7 m 2 Vs was found to be indirect allowed at 1.65 eV; other interband transitions are at 2.3 and 3.5 eV.
TL;DR: In this paper, the molecular beam epitaxial growth of GaP on Si was investigated, with the aim of at least approaching device-quality interfaces, and a tentative energy band lineup was proposed, which was consistent with the electrical data.
Abstract: The molecular‐beam epitaxial growth of GaP on Si was investigated, with the aim of at least approaching device‐quality interfaces. Gallium‐primed growth on (211)‐oriented substrates yielded layers which were free of antiphase domains, and which were of much higher quality than growths on other orientations. A tentative energy‐band lineup is proposed, which is consistent with the electrical data. Heterojunction bipolar transistors were fabricated with emitter injection efficiencies up to 90%, in spite of indications that the epitaxial emitter layer was far less heavily doped than the base.
TL;DR: The influence of surface recombination on photocurrents at the illuminated semiconductor/electrolyte interface is considered in this paper, where the surface states are located at a discrete energy in the band gap and communicate preferentially with the semiconductor.
01 Feb 1984
TL;DR: In this article, the authors review and extend the theory of electron and hole motion and density in solids with position-dependent band structure, including materials with graded composition, like heterojunctions, with nonuniform temperature or strain, and devices with highly doped regions.
Abstract: This paper reviews and extends the theory of electron and hole motion and density in solids with position-dependent band structure. This includes materials with graded composition, like heterojunctions, with nonuniform temperature or strain, and devices with highly doped regions, like the emitter region of modern bipolar transistors and solar cells. Size effects, such as those in short-channel MOS transistors, are not considered. Changes in the energy band edges due to spatial variations in electron affinity and bandgap and changes in the density of states produce terms in the carrier- and current-density equations in addition to those found in the conventional Shockley model. This paper emphasizes the physical concepts underlying these modifications and provides a theoretical framework from which experimental results can be correctly interpreted. The new effects are derived and discussed. Areas which require further research are pointed out. The paper discusses the validity and meaning of a nonuniform band structure. The general energy-band diagram relating the electrostatic potential, the electron affinity, and the bandgap is given. Expressions for current density are derived from a solution of the Boltzmann equation. Expressions for nonequilibrium carrier densities are presented. The effective mass approximation and the rigid band model are discussed. The concepts of generalized drift and diffusion are established and alternative formulations are given. Various device applications including minority-carrier flow in quasi-neutral regions are also given.
TL;DR: In this paper, low-temperature photoluminescence and excitation spectroscopy measurements on heavily doped (up to 4mmode/times/else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) $n$- and $p$-type silicon are reported.
Abstract: Low-temperature photoluminescence and excitation spectroscopy measurements on heavily doped (up to 4\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) $n$- and $p$-type silicon are reported. From the luminescence spectra values for the optical and the reduced band gap are deduced and compared with theoretical calculations. The shrinkage of the reduced band gap follows an ${n}^{\frac{1}{3}}$ law for carrier concentrations $n$ above the critical Mott density. Both $n$- and $p$-type samples show an identical shift of the reduced gap, whereas the shift of the optical gap is different due to the different density-of-states masses for electrons and holes. From photoluminescence excitation spectra the position of the optical gap is determined independently. A good agreement of the data obtained by these selective absorption measurements with the results from conventional luminescence spectra is found.
TL;DR: In this paper, the first-order Raman scattering by TO and LO phonons has been measured in GaSb, InAs, and InSb under hydrostatic pressures up to their phase transitions.
Abstract: The first-order Raman scattering by TO and LO phonons has been measured in GaSb, InAs, and InSb under hydrostatic pressures up to their phase transitions. The Raman frequencies increase nearly linearly while the LO-TO splitting decreases with increasing pressure. The scattering intensities display strong enhancement as the ${E}_{1}$ band gaps approach the laser frequencies with increasing pressure. The measured volume dependence of the Raman frequencies and the transverse effective charges is interpreted by means of pseudopotential calculations. The resonance behavior is discussed in terms of resonant Raman scattering near the ${E}_{1}$ gaps.
TL;DR: In this article, the authors observed the characteristic behavior of a 2D electron plasma in optical emission and absorption across the energy gaps in modulation-doped GaAs-(AlGa)As quantum-well heterostructures.
TL;DR: In this article, the electronic structures of the two polymorphic forms of lead monoxide (PbO), red tetragonal..cap alpha, and yellow orthorhombic..beta, are investigated by using extended Hueckel tight-binding calculations.
Abstract: The electronic structures of the two polymorphic forms of lead monoxide (PbO), red tetragonal ..cap alpha..-PbO and yellow orthorhombic ..beta..-PbO, are investigated by using extended Hueckel tight-binding calculations. The band structures and bonding are analyzed within the layers and also for the complete three-dimensional solids. In red ..cap alpha..-PbO a local energy minimum is obtained when the layers are stacked together. For yellow ..beta..-PbO, the bonding is studied starting from PbO subunits and building successively chains, layers, and the three-dimensional solid. Bonding between chains occurs mainly through Pb-O but Pb-Pb bonding interactions are also significant. In both ..cap alpha.. and ..beta.. modifications weak interlayer Pb-Pb bonding is found which may not be the result of van der Waals attraction. Crystal orbital overlap populations provide a convenient view of the bonding in the two solids. Within the layers, these values correlate satisfactorily with the force constants calculated from experimental data. It is suggested that a more strongly bound material could be synthesized if either PbO structure should have electrons removed from it.
TL;DR: In this article, the authors compared the theoretical and experimental emission energy of a single quantum well with the theoretical curves generated from a finite potential square well model and found that the closest agreement between the experimental and theoretical curves occurs when the conduction band discontinuity is taken to be 70% of the band gap discontinuity or 0.52 eV.
Abstract: Photoluminescence studies at 4 K on Ga0.47In0.53As/ Al0.48In0.52As single quantum wells exhibit emission ranging from 1.318 eV for a 15‐A well to 0.82 eV for thick wells. The emission energy of each single quantum well is compared to theoretical curves which are generated from a finite potential square well model. The closest agreement between the experimental curves and the theoretical curves occurs when the conduction band discontinuity is taken to be 70% of the band‐gap discontinuity or 0.52 eV.
Patent•
12 Apr 1984TL;DR: In this article, the open circuit voltage and efficiency of photovoltaic devices formed from multiple regions of semiconductor alloys including at least one narrow band gap semiconductor alloy are enhanced.
Abstract: The open circuit voltage and efficiency of photovoltaic devices formed from multiple regions of semiconductor alloys including at least one narrow band gap semiconductor alloy are enhanced. The device includes a pair of doped regions and an intrinsic body between the doped regions. The intrinsic body includes a first intrinsic region and an open circuit voltage enhancement means including a second intrinsic region. The second intrinsic region has a wider band gap than the band gap of the first intrinsic region and is disposed between the first intrinsic region and one of the doped regions. The open circuit enhancement means can also include a third intrinsic region also having a wider band gap than the first intrinsic region and disposed on the side of the first intrinsic region opposite the second intrinsic region.
TL;DR: In this paper, the annealing kinetics of the two levels are studied and it is found that EL6 vanishes by a pair-defect (short-range) type recombination while the U band anneals by a long range migration process.
Abstract: Fast neutron irradiation of n‐GaAs mainly induces two deep electron traps in the band gap. The first of these is referred to as EL6 and has an energy level at Ec −0.35 eV, where Ec is the conduction band minimum; the second one has a wide energy distribution around Ec −0.5 V and is referred to as the U band. The annealing kinetics of these two levels is studied, and it is found that EL6 vanishes by a pair‐defect (short‐range) type recombination while the U band anneals by a long range migration process. Both annealing processes can be observed between 400 and 500 °C. In this annealing temperature range, the concentration of deep donor level EL2 (Ec −0.75 eV) increases with temperature. It is suggested that the defect giving rise to the EL2 level is created during irradiation but that medium range (tens to hundreds of A) interactions with other neighboring defects strongly influence the electric properties of the overall defect, which is then detected as the U band. Due to long range migration, annealing r...
TL;DR: In this article, the authors used augmented plane wave (APW) calculations for CsI to generate the band structure, the static lattice equation of state (EOS), and the volume dependence of the electronic energy-band gap.
Abstract: Self-consistent, nonrelativistic augmented-plane-wave (APW) calculations for CsI were carried out to generate the band structure, the static-lattice equation of state (EOS), and the volume dependence of the electronic energy-band gap. The theoretical room-temperature isothermal compression curve agrees well with static and ultrasonic measurements at low pressure. Our calculations do not agree with two recent sets of diamond-anvil-cell measurements above 10 GPa. The calculated band gaps are too small at low pressure, but, at high pressure, are consistent with both the experimental results and the Herzfeld-model prediction. These results suggest that the insulator-to-metal transition occurs in the range 100 +- 10 GPa. A calculation of the shock compression curve of CsI shows that the thermally excited electrons cause a significant softening of the Hugoniot curve. The experimental zero-pressure band gaps of the isoelectronic compounds Xe, CsI, and BaTe are linearly correlated with ln(v/v/sub H/), where v/sub H/ is the specific volume of metallization predicted by the Herzfeld model. Based on this correlation, and on the similarity of the APW calculated EOS's of Xe and CsI, which agree closely with experimental compression measurements, we predict that BaTe will become metallic at approximately 30 GPa.
IBM1
TL;DR: In this paper, the authors employed the techniques of photoelectron spectroscopy (with tunable synchrotron radiation $30.6$ eV) and inverse photoemission spectroscopic at $h\ensuremath{
u}=9.7$ ev to study respectively the occupied and unoccupied electronic states of $n$-type (SrTiO))-type.
Abstract: We have employed the techniques of photoelectron spectroscopy (with tunable synchrotron radiation $30\ensuremath{\le}h\ensuremath{
u}\ensuremath{\le}100$ eV) and inverse photoemission spectroscopy at $h\ensuremath{
u}=9.7$ eV to study respectively the occupied and unoccupied electronic states of $n$-type ${\mathrm{SrTiO}}_{3}$ doped with 1 at.% Nb. Doped samples have the advantage that charging effects are avoided and hence a rather accurate determination of peak positions is possible. The total (occupied and empty) experimental density of states agrees with the calculated density of states of Pertosa and Michel-Calendini when their band-gap energy is readjusted. We have no evidence for intrinsic surface states either in the band gap or in the conduction band, as was calculated by Wolfram et al. The admixture of Ti $3d$ states in the O $2p$ valence states is small, as can be concluded from the Ti $3p\ensuremath{\rightarrow}3d$ resonance behavior.