Showing papers on "Band gap published in 1979"
533 citations
TL;DR: In this article, a theory was presented which quantitatively accounts for the important features of conduction in ZnO-based metaloxide varistors, which predicts a varistor breakdown voltage of 3.2 V/grain boundary for n0=1017 carriers' cm−3 and T=300 K.
Abstract: A theory is presented which quantitatively accounts for the important features of conduction in ZnO‐based metal‐oxide varistors. This theory has no adjustable parameters. Using the known values of the ZnO band gap, donor concentration n0, and low‐voltage varistor leakage‐current activation energy, we predict a varistor breakdown voltage of ?3.2 V/grain boundary for n0=1017 carriers cm−3 and T=300 °K. This compares well with measurements on a single grain‐grain junction. The highly nonlinear varistor conduction derives from electron tunneling ’’triggered’’ by hole creation in the ZnO when the conduction band in the grain interior drops below the top of the valence band at the grain interface. The theory predicts coefficients of nonlinearity α=d (lnI)/d (lnV) as high as 50, or even 100.
427 citations
TL;DR: In this article, the quantum efficiency of photoelectrolysis of water, using semiconducting oxide anodes of high conductivity (≈ 1 Ωcm), is used to determine the energies of the interband transitions of the oxides.
266 citations
TL;DR: The spectral dependence of the absorption coefficient of silicon for photon energies up to 2.7 eV was determined for several temperatures in the range 298-473 K as discussed by the authors, where the effect of a temperature increase appears as a red shift of the spectrum.
Abstract: The spectral dependence of the absorption coefficient of silicon for photon energies up to 2.7 eV was determined for several temperatures in the range 298–473 K. The effect of a temperature increase appears as a red shift of the absorption spectrum. The magnitude of the shift is larger than that of the fundamental energy gap, increases with increasing photon energy in the range 1.1–1.7 eV, and is constant for energies greater than 1.7 eV. A phenomenological expression deduced by analysis of the data may be used to calculate α (E) at elevated temperature, given α (E) at room temperature. The reflectance was also measured at 299, 413, and 516 K in the photon energy range 2.5–3.8 eV.
258 citations
TL;DR: In this paper, the authors proposed a superlattice which consists of alternating (100) layers of CdTe and HgTe and the band gap can be adjustable from 0 to 1.6 eV depending on the thicknesses of the layers.
Abstract: We propose a new material which could be useful in a number of infrared optoelectronic devices. The material consists of alternating (100) layers of CdTe and HgTe. The band gap of this superlattice is adjustable from 0 to 1.6 eV depending on the thicknesses of the CdTe and HgTe layers. Details of the band‐gap variation and the character of the band‐edge states are presented.
218 citations
TL;DR: In this article, a tight-binding method with scaled two-centre interactions was used to calculate the energy and nature of the upper valence bands of SnO2 and the calculated joint density of states for the experimentally observed optical dispersion.
Abstract: The band structures and densities of states for a number of non-transition-metal compounds with the rutile structure are calculated using a tight-binding method with scaled two-centre interactions. For SnO2, the valence band maximum state is calculated to have Gamma 3+ symmetry in agreement with experimental results, and the calculated valence-band density of states is in fair agreement with photoemission. The simplicity of the LCAO approach is utilised to give algebraic expressions for the energy and nature of each band and used to discuss bonding and ionicity. The importance of the long-pair oxygen orbitals in forming the upper valence bands of SnO2 is stressed. TeO2 is discussed as an example of a class of compounds in which the two cation s electrons remain bound, giving rise to a cationic gap. The calculated joint density of states can be used to account for the experimentally observed optical dispersion.
200 citations
TL;DR: In this paper, the secondary-electron spectra were excited by Al-$K\ensuremath{\alpha}$ (1487 eV) photons and were measured from evaporated dielectric films with an electrostatic hemispherical analyzer of about 0.03-eV resolution.
Abstract: Secondary-electron energy distribution curves (EDC's) and the total secondary-electron yields relative to such for gold have been measured for seven semiconductors for which electron-electron scattering losses within the emitter were considered dominant and for nine insulators (alkali halides) for which electron-phonon scattering losses were expected to be dominant in the transport process. The secondary-electron spectra were excited by Al-$K\ensuremath{\alpha}$ (1487 eV) photons and were measured from evaporated dielectric films (of about 0.3 \ensuremath{\mu} thickness) on conducting substrates with an electrostatic hemispherical analyzer of about 0.03-eV resolution. Some of the dielectric photoemitters have appreciably narrower energy distributions and higher yields than has gold; CuI and CsI have EDC widths at half-maximum of about one-third of that for gold, and yield values of 11 and 30 times greater. The FWHM and secondary-electron yield for gold were measured to be about 4 eV and 0.50 electrons per normally incident photon, respectively. The shapes of the EDC's were found to be essentially unchanged for photon excitation in the 0.1-10-keV region. Strong structural features appear only in the alkali halide EDC's, and it is proposed that these are mainly the result of single-electron promotion of secondaries from the valence band by plasmon deexcitation. A relatively simple model for x-ray photoemission has been developed which assumes that direct excitation of secondaries by photoelectron and Auger-electron "primaries" is the dominant excitation mechanism, and accounts for both electron-electron and electron-phonon scattering in the transport process. Free-electron conduction-band descriptions are assumed. The theoretical and experimental curves are in satisfactory agreement.
199 citations
TL;DR: In this paper, the authors interpreted the absorption of AlN thin films as excitonic absorptions due to transitions across the direct energy gap of about 6.2 eV and 7.8 eV.
Abstract: Optical absorption of AlN thin films shows a ’’knee’’ structure at 6.2 eV and an intense band at 7.8 eV. The structure at 6.2 eV is interpreted as excitonic absorptions due to transitions across the direct energy gap of about 6.2 eV. Dichroism observed at the absorption edge indicates that the transition Γ1v–Γ1c (E∥c) is of lower energy than the transition Γ6v–Γ1c (E⊥c). Strong dichroism in the 7–8‐eV region is thought to cause the birefringence of AlN.
190 citations
TL;DR: In this paper, the ESR spectrum consists of two structures: a relatively broad line A with g-value and linewidth depending considerably on composition, particularly after irradiation with He+-ions of 250 keV energy, and a narrow line B with g ≈ 2.5.
Abstract: Amorphous SiOx-layers with O < x < 2 have been prepared by evaporation of Si at oxygen pressures of 10−6 … 10−3 mbar. The composition of the samples was determined by proton backscattering. The band gap, derived from optical measurements, increases with rising oxygen content relatively little at first and the main enhancement occurs above x = 1.5. The ESR spectrum consists of two structures: (1) a relatively broad line A with g-value and linewidth depending considerably on composition, particularly after irradiation with He+-ions of 250 keV energy, and (2) a narrow line B with g ≈ 2.0001 which corresponds to the E′-center in SiO2 and increases in intensity with rising oxygen content. The properties of the broad line A can be described by a superposition of 3 lines with different g-values and linewidths. The hopping conductivity after He+-irradiation decreases strongly with increasing oxygen content indicating that the E′-center does not contribute to the hopping transport.
148 citations
TL;DR: In this paper, the electrical resistivity and Hall effect of p-and n-type CuInSe2 single crystals are measured in the temperature range from 80 K to 500 K.
Abstract: The electrical resistivity and Hall effect of p- and n-type CuInSe2 single crystals are measured in the temperature range from 80 K to 500 K p- and n-type samples are prepared by doping with excess Se and excess In, respectively The acceptor levels at 0020 eV and 0028 eV above the valence band and the donor levels at 0012 eV and 018 eV below the conduction band are identified The mobility data are analysed assuming scattering by acoustic, polar optical, and nonpolar optical phonons and by ionized impurities For some of the n-type samples, the measurements are extended to liquid helium temperature and the result is analysed by the existing theories of impurity band conduction
146 citations
TL;DR: The optical constants of amorphous thin films of Sb2S3 prepared by vacuum evaporation were determined by means of transmission electron microscopy as discussed by the authors, and the optical constants in the amorphized films are rather structureless but on crystallization several structures are observed in e2 at energies of 1.88, 2.48, 3.86 and 5.25 eV.
TL;DR: In this paper, an effective Hamiltonian, acting in the eightfold space of the valence band and the lowest conduction band of a zinc-blende-type material, is constructed by invariant expansion.
Abstract: Quantum resonances in the valence bands of semiconductors under uniaxial stress provide very detailed information on the band parameters if the experimental data can be analyzed on the basis of an adequate theoretical model. Such a model has been developed for and applied to Ge by Hensel and Suzuki and yielded high-precision band parameters for this material. The theory which is based on the invariant expansion of the valence-band Hamiltonian and makes use of the symmetry of the diamond lattice fails, however, to explain similar experiments for InSb. The reason for this failure is twofold: The reduced symmetry of the zinc-blende lattice makes it necessary to consider inversion-asymmetry-induced contributions to the effective Hamiltonian; the small gap of InSb requires an exact treatment of the couplings between valence band and lowest conduction band. Here we present a theory to overcome these difficulties. An effective Hamiltonian, acting in the eightfold space of the valence band and the lowest conduction band of a zinc-blende-type material, is constructed by invariant expansion. For this purpose the method of invariants is extended to the cross space between valence band and conduction band on the basis of the angular momentum calculus. The Hamiltonian describes the Landau levels of valence and conduction bands under uniaxial stress for magnetic fields (parallel to the stress) along the high-symmetry [001], [111], and [110] directions. Since the Hamiltonian is constructed on group-theoretical grounds, the eigenstates can be classified according to their transformation properties, and selection rules are given for both inter- and intraband transitions.
TL;DR: In this article, the use of semiconductors as photoelectrodes in electrolytic cells for the electrolysis of water is described and the results reported in the literature for various semiconductor properties are reviewed.
Abstract: The use of semiconductors, as photoelectrodes in electrolytic cells for the electrolysis of water, is described and the results reported in the literature for various semiconductors are reviewed. The most important properties of the semiconductor are shown to be the band-gap energyE g , and the flat-band potentialU fb . The semiconductor absorbs photons that are more energetic than the band-gap energy and creates electronhole pairs. These charge carriers can be separated before recombination by the electric field at the semiconductor-electrolyte interface. For electrolysis to proceed, the potential corresponding to the band gap must appreciably exceed the standard potential for the electrolysis of water, 1.23 volts. In addition, the flat-band potential must be more negative than the hydrogen potential or an external bias voltage is required. The semiconductor must not corrode under the operating conditions and must permit transfer of the minority carrier to the electrolyte. The current theories of charge transfer and reaction mechanism are discussed.
Patent•
31 Dec 1979TL;DR: In this article, a multijunction photovoltaic solar cell for use with a concentration lens was proposed, which consists of an elemental single crystal substrate without an internal light sensitive junction, upon which are two or more successive homogenous layers of semiconductor materials.
Abstract: A new high efficiency, multijunction photovoltaic solar cell for use with a concentration lens. This cell comprises an elemental single crystal substrate without an internal light sensitive junction, upon which are two or more successive homogenous layers of semiconductor materials, each layer containing within it a light sensitive p/n junction of a similar polarity, each layer having essentially the same lattice constant as the single crystal substrate, each layer having a shorting junction contact with the layer immediately above and below it, each successive layer adsorbing light energy at a shorter wavelength, and each layer being of sufficient thickness and appropriate composition to develop essentially the same current as the other layers. At the junction, between the successive layers of the multilayer cell, a thin pseudo transparent low bandgap semiconductor layer is provided at the shorting junction interface. The outer surfaces of the top layer and the substrate are provided with electrical contacts for distribution of the electric current. The top contact comprises a layer of a transparent conductive material with electrical connections and the whole structure is completed with an antireflection coating over the top.
15 Nov 1979
TL;DR: In this paper, the photoionization threshold of tryptophan was extended to indole as a solute, both in tetramethylsilane (TMSi) and H 2 O solvents.
Abstract: Previous work on the determination of the photoionization threshold ( I sol ) of tryptophan has now been extended to indole as a solute, both in tetramethylsilane (TMSi) and H 2 O solvents. In TMSi, electron scavenging by N 2 O or photoconductivity measurements lead to the same I sol value: 4.95 ± 0.1 eV. In water, I sol is found equal to 4.35 ± 0.1 eV. From these experiments, information on the ionization mechanism, on the oxidized solute and on the solvent can be gained: (i) the scavenger electron affinity does not intervene in the energy balance providing I sol ; (ii) an “effective” ionic radius of indole (1.40 A) is estimated which suggests that the positive charge remains highly localized on the N-atom of the indole ring; (iii) a value of −1.2 ± 0.1 eV can be deduced for V o , the conduction band edge of water; (iiii) from the above findings, the energy gap E G of pure water, considered as a semi-conductor, would be close to 7 eV. Such a result is discussed in terms of literature data pertaining to electron ejection in pure liquid water and X-ray photoelectron spectroscopy of amorphous ice.
TL;DR: In this article, the band structures of the layer compounds SnS2, SnSe2, CdI2 and PbI2 are calculated by the tight-binding method, and a universal band structure for the family is found by use of approximate algebraic band energies.
Abstract: The band structures of the layer compounds SnS2, SnSe2, CdI2 and PbI2 are calculated by the tight-binding method. They are in closer agreement with experimental results and previous pseudopotential calculations than previous tight-binding results have been. A universal band structure for the family is found by use of approximate algebraic band energies. For the 16-electron crystals a Gamma 2- to L1+ indirect gap and a main optical transition due to anion p-cation p orbitals is found, whilst for PbI2 the gap is direct at A.
TL;DR: In this article, six-cycle-Hz films have been prepared at 200°C by reactive plasma deposition from SiH4 and CH4 diluted in helium in a tubular reactor.
TL;DR: In this article, a study of the electrical, optical and photoconducting properties of pure and reduced single crystals of composition Fe 2− x Cr x O 3 where 0 ⩽ x⩽ 0.47 is the optical band gap.
TL;DR: In this article, a simple physical model is proposed to estimate the amount of charge transfer, which has been a matter of controversy in graphite intercalation compounds, and the band structure of C 8 K is calculated self-consistently by the present method.
Abstract: The method of the band structure calculation for layer-type materials is presented with use of atomic pseudopotentials and the Madelung-type potential due to the charge transfer. A simple physical model is proposed in order to estimate the amount of charge transfer, which has been a matter of controversy in graphite intercalation compounds. The band structure of C 8 K is calculated self-consistently by the present method and the amount of the charge transfer is determined non-empirically to be 0.6. The obtained band structure is almost the same as that calculated by the tight binding method.
TL;DR: In this article, a theoretical calculation and experimental data on the effective third-order susceptibilities χ(3) for degenerate four-wave mixing near the band gap of semiconductors are presented.
Abstract: We present a theoretical calculation and experimental data on the effective third‐order susceptibilities χ(3) for degenerate four‐wave mixing near the band gap of semiconductors. The closeness of the calculated and experimental values for the effective χ(3) in silicon at 1.06 μm indicates the utility of our simple calculation. The large values of χ(3) indicate the possibility of high‐efficiency degenerate four‐wave mixing in semiconductors, especially at longer wavelengths.
TL;DR: The optical transmittance of thin PdO films has been measured in the range 0.5-5.4 eV by Kramers-Kronig analysis as mentioned in this paper.
Abstract: The optical transmittance of thin PdO films has been measured in the range 0.5-5.4 eV. From these data the optical constants have been determined by Kramers-Kronig analysis. A small band gap (0.8 eV) and a high dielectric constant (8.0) have been found.
TL;DR: In this paper, the effect of the lighting configuration on spectral PV plots is discussed, and the origin of two peaks of PV responses is interpreted as being in accordance with optical data.
Patent•
13 Apr 1979TL;DR: In this paper, a multilayered GaAs structure is proposed to enhance the mobility of GaAs using molecular beam epitaxy (MBE) to enhance GaAs mobility.
Abstract: The mobility of a relatively narrow bandgap semiconductor material can be significantly enhanced by incorporating it into a multilayered structure (10) comprising a first plurality of layers (12) of a relatively narrow bandgap form of the material and a second plurality of wider bandgap semiconductor layers (14) interleaved with and contiguous with the first plurality. The wide bandgap and narrow bandgap layers are substantially lattice-matched to one another, and the wide bandgap layers are doped such that its product of impurity concentration and thickness is greater than the same product in the narrow bandgap layers. The fabrication of the structure by molecular beam epitaxy (MBE) to enhance the mobility of GaAs is specifically described. In this case, the narrow bandgap layers (12) comprise GaAs and are unintentionally doped to about 1014/cm3, whereas the wide bandgap layers (14) comprise AlGaAs doped n-type to about 1016 to 1018/cm3. The incorporation of this structure in an FET is also described.
TL;DR: In this article, self-consistent APW calculations of the electronic energy bandstructure of the calcium hexaboride, CaB6, are reported, in the muffin-tin approximation and in the warped muffintin approximation.
Abstract: The calcium hexaboride, CaB6, is a typical semiconducting metal hexaboride. Here two self-consistent APW calculations of its electronic energy bandstructure are reported, in the muffin-tin approximation and in the warped muffin-tin approximation. In both calculations, the local-spin-density approximation is used and the relativistic effects are taken into account. The bandstructure of the muffin-tin approximation is semimetallic. The non-muffin-tin corrections in the warped muffin-tin approximation tends to cause a small, direct energy gap between the valence and conduction bands at the X points in the simple cubic Brillouin zone. The magnitude of the energy gap to 0.3 eV, in reasonable agreement with the experimental value, 0.4 eV, suggested by the temperature dependence of the electrical resistivity. The calculated result for the density of states agrees reasonably well with an experimental result for the XPS spectrum.
TL;DR: In this paper, the basic interface properties of GaAs metal-oxide-semiconductor (MOS) structures formed using an anodic oxidation process in a mixed solution of glycol and water (the AGW process) were investigated.
TL;DR: In this paper, a new model of electronic density of states distribution including the influence of the grain boundary has been constructed for the consistent interpretation of the observed characteristics, and a substantial difference between the present model and a Schottky barrier model is also discussed.
Abstract: For the systematic understanding of polycrystalline silicon, the conduction mechanisms, optical absorption processes, and recombination kinetics have been investigated. Tailing states as well as deep levels in the energy gap are found in activation energies of photoconductivity, high densities of ESR centers, and optical absorption tails at photon energies below the energy gap. A new model of electronic density‐of‐states distribution including the influence of the grain boundary has been constructed for the consistent interpretation of the observed characteristics. A substantial difference between the present model and a Schottky barrier model is also discussed.
01 Jul 1979
TL;DR: In this paper, a comparative study of molybdenum and tungsten-dichalcogenides in contact with various redox electrolytes revealed that in absolute values as well as in relation to the energy gap, n-type WSe2 is producing the largest photopotential output.
Abstract: A comparative study of molybdenum- and tungsten-dichalcogenides in contact with various redox electrolytes revealed that in absolute values as well as in relation to the energy gap, n-type WSe2 is producing the largest photopotential output. It exceeds 0.55 Volt in presence of several redox couples (Fe2+/3+, H2Q/Q pH = 10, Fe(CN)3-/4-, 6, Ru3-/4+, Br−/Br2, Ce3+/4+) and amounts to more than 0.7 Volt in presence of I−/I2. Addition of small quantities of iodide can increase the photopotential output in presence of redox systems with lower redox potential by up to 0.1 Volt. This gives further evidence for the specific photochemical surface activity of iodide on layer-type electrodes and is an example for the influence of surface states on the efficiency of energy conversion. - The higher photopotential output of WSe2 as compared to that of MoSe2 (maximum value I−/I2:0.56 Volt) is explained in terms of a negative shift of the conduction band edge. With respect to the efficiency of electrochemical solar energy conversion WSe2 is considered to be the most promising compound among layer-type d-band semiconductors.
Eine vergleichende Studie von Molybdan- und Wolframdichalkogeniden in Kontakt mit verschiedenen Redox-Elektrolyten ergab. das, in absoluten Werten wie auch im Verhaltnis zur Energie-Lucke, n-leitendes WSe2 das hochste Photopotential liefert. Es ubertrifft 0,55 Volt in Gegenwart von mehreren Redox-Paaren (Fe2+/3+, Hydrochinon/Chinon (pH = 10), Fe(CN)3-/4-, 6, Ru3-/4+, Br−/Br2, Ce3+/4+) und betragt mehr als 0,7 Volt in Gegenwart von I−/I2. Zugaben von kleinen Mengen von Jodid konnen in Gegenwart von Redox-Systemen mit niedrigerem Redox-Potential das Photopotential um bis zu 0,1 Volt erhohen. Das ist ein weiterer Hinweis auf die spezifische photochemische Oberflachenaktivitat von Jodid an Schichtgitter-Elektroden und ein Beispiel fur den Einflus von Oberflachenzustanden auf die Wirksamkeit der Energieumwandlung Das im Vergleich zum MoSe2 (Maximalwert: I−/I2: 0,56 Volt) hohere Photopotential von WSe2 wird durch eine negative Verschiebung des Leitungsbandes erklart. Im Hinblick auf die Wirksamkeit der elektrochemischen Sonnenenergieumwandlung wird WSe2 als die vielversprechendste Verbindung unter den schichtartigen d-Band-Halbleitern angesehen.
TL;DR: In this paper, a defect mechanism responsible for pinning states within the band gap on the (110) surfaces of the III-V compounds is presented. But the defect mechanism is not considered in this paper.
Abstract: New evidence for a defect mechanism which is responsible for pinning states within the band gap on the (110) surfaces of the III–V compounds is presented. Investigations of column III metals on both n‐ and p‐type GaAs revealed a systematic difference in surface Fermi energy stabilization in the gap with p‐type samples pinning 0.25 eV below n‐type samples. Several current models and theories of Schottky barriers are discussed in terms of both the results given in this paper and previously reported data.
TL;DR: In this article, a simple method based on the linear relationship between experimental metal work functions and Pauling electronegativities has been used to obtain effective solid state Fermi energies for atoms, both metallic and nonmetallic.
Abstract: A simple method based on the linear relationship between experimental metal work functions and Pauling electronegativities has been used to obtain effective solid state Fermi energies for atoms, both metallic and nonmetallic. A simple arithmetic mean combination rule was used to give the intrinsic Fermi level of a solid, and this level was then combined with band gap data to give electron affinities. The method was applied to materials covering a wide range of band gaps and ionicity. The results were in good agreement with literature values of electron affinities.