Showing papers on "Band gap published in 1974"
TL;DR: In this article, the band gap energy of silicon has been evaluated with high precision between 2 and 300 K by the following method: the derivative of the absorption coefficient, resulting from free exciton absorption, has a well-defined singularity, which can be detected unambiguously by wavelength-modulation spectroscopy.
Abstract: The band‐gap energy Eg of silicon has been reevaluated with high precision between 2 and 300 K by the following method: the derivative of the absorption coefficient, resulting from free‐exciton absorption, has a well‐defined singularity, which can be detected unambiguously by wavelength‐modulation spectroscopy. The energy of this singularity yields the band gap. Our data deviated by more than 5 meV from the earlier results of MacFarlane et al. and Haynes et al. and fell between their Eg(T) curves. The approximation of Eg(T) = A + BT + CT2 gives A = 1.170 eV, B = 1.059×10−5 eV/K, and C = −6.05×10−7 eV/K2, for 0
466 citations
TL;DR: In this article, the electron states of an indirect optical semiconductor with two bands were calculated in the presence of an additional periodic one-dimensional potential (superlattice) in the semiconductor material.
Abstract: Starting from a model of an indirect optical semiconductor with two bands, the electron states are calculated in the presence of an additional periodic one-dimensional potential (superlattice) in the semiconductor material. These states are used to determine the transition probability connected with the absorption of a photon. This transition corresponds to an optical direct transition — no phonon takes part in this process. The optical direct and optical indirect transitions are compared. For optical frequencies near the band gap one expects only direct transitions, whereby the optical indirect transitions may be neglected.
207 citations
TL;DR: In this article, Fowler-Nordheim tunneling was shown to be consistent with elastic tunneling into the silicon direct conduction band and, at still lower fields, inelastic tunnelling into the indirect conduction bands.
Abstract: Recent results on tunneling in thin MOS structures are described. Thermally grown SiO2 films in the thickness range of 22-40 A have been shown to be effectively uniform on an atomic scale and exhibit an extremely abrupt oxide-silicon interface. Resonant reflections are observed at this interface for Fowler-Nordheim tunneling and are shown to agree with the exact theory for a trapezoidal barrier. Tunneling at lower fields is consistent with elastic tunneling into the silicon direct conduction band and, at still lower fields, inelastic tunneling into the indirect conduction band. Approximate dispersion relations are obtained over portions of the silicon-dioxide energy gap and conduction band.
198 citations
TL;DR: The physical origin of the bowing of energy gaps in semiconductor alloys is considered in this paper, where it is shown that disorder plays no significant part in energy gap bowing.
Abstract: The physical origin of the bowing of energy gaps in semiconductor alloys is considered. It is shown that disorder plays no significant part in energy-gap bowing, and that the virtual crystal approximation is valid. An expression is derived for the bowing resulting from the nonlinear dependence of the crystal potential on the properties of the component ions, and very good agreement is found with experimental data for sixteen alloys at the Gamma point ad eight alloys at the L point.
191 citations
TL;DR: Theoretical and experimental results for the band structure of polyethylene are presented in this paper, where an energy gap of 7.5 ± 0.5 eV and a C1s line at 284.6 eV are deduced.
Abstract: Theoretical and experimental results for the band structure of polyethylene are presented. Theoretical results are obtained from both semiempirical (CNDO/2 and extended Huckel) and nonempirical methods. The density of states is measured by the ESCA method. An energy gap of 7.5 ± 0.5 eV and a C1s line at 284.6 eV are deduced. Although CNDO/2 results appear to be unreliable, the correlation between theory and observed density of states is found to be very good for extended Huckel and ab initio results.
180 citations
TL;DR: In this paper, molecular orbitals for the highest occupied states of TTF + and TCNQ −, calculated by the Extended Huckel Method of Hoffman, are used to compute band parameters within the tight-binding approximation for the conduction band of solid TTFTCNQ.
159 citations
TL;DR: In this article, a minimum value for the band gap of 6.4 ± 0.5 eV was obtained from soft X-ray spectra of cubic boron nitride crystals.
156 citations
TL;DR: In this article, the energy band structure of stannic oxide has been calculated by a self-consistent augmented plane wave (APW) method, which predicts SnO 2 to be a semiconductor with an allowed direct band gap of 3·68 eV for light polarized perpendicular to the tetragonal axis.
146 citations
TL;DR: In this paper, the inversion asymmetry splitting of the spin degeneracy is investigated for a narrow-gap semiconductor with the zinc-blend structure. But the analysis of the Schubnikov-de Haas measurements of Hg 0.79 Cd 0.21 (e G =68 meV, m 0 * = 0.006 m).
Abstract: Quantized surface states in an inversion later of narrow-gap semiconductor with the zinc-blend structure are investigated theoretically by the effective mass approximation for nearly degenerate bands. When the band gap is small, and the spin-orbit interaction is large, the inversion asymmetry of surface potentioal causes large k -linear term in the two dimensional dispersion relation, which removes the spin degeneracy. Also, the g -factor becomes so large that the reversal of the ordering of the Landau levels is expected. The theory is applied to the analysis of the Schubnikov-de Haas measurements of Hg 0.79 Cd 0.21 ( e G =68 meV, m 0 * =0.006 m). The inversion asymmetry splitting of the spin degeneracy is as large as several meV, and the inversion in the order of Landau levels is expected to be observed. The surface potentioal of the sample is expressed in the parametrized form, and values of the parameters are estimated by using the experimental data.
139 citations
118 citations
TL;DR: In this paper, a three-layered AlxGa1−xAs-GaAs-Alx GaAs structure has been used to measure the optical absorption and photoluminescence in thin GaAs layers prepared by liquid phase epitaxy.
Abstract: A three‐layered AlxGa1−xAs–GaAs–Alx Ga1−xAs structure has been used to measure the optical absorption and photoluminescence in thin GaAs layers prepared by liquid‐phase epitaxy. The results presented here are for lightly doped n‐type GaAs with free‐carrier concentrations near 1016 cm−3; however, the technique can be used for arbitrarily doped material. The absorption coefficient α was measured between 1.4 and 2.2 eV at 2 and 298 K. The absorption strength at the band gap was found to be (1.15×104)±1000 cm−1 at 2 K and (0.99×104)±1000 cm−1 at 298 K. At 1.96 eV, the energy of the He–Ne laser commonly used for photoexcitation of GaAs, α at 298 K was measured to be 4.4×104 cm−1. A value of 3.8 meV for the room‐temperature exciton binding energy was inferred from the temperature dependence of the interband absorption strength. This value together with previous reflectivity data for high‐purity GaAs gives the energy gap of pure unstrained GaAs at 298 K as 1.424±0.001 eV. The effects of strain due to lattice mis...
TL;DR: In this article, the pressure dependence of energy gaps for a number of elemental and compound semiconductors is investigated employing the empirical pseudopotential method, and the results are good for elemental semiconductor and reasonable for III-V compounds.
Abstract: The pressure dependence of energy gaps for a number of elemental and compound semiconductors is investigated employing the empirical pseudopotential method. The compressibility and the empirical pseudopotential form factors appropriate for describing the band structure at normal pressure are the only required input parameters in this calculation. The calculated pressure coefficients of several critical-point band gaps for group IV and III-V compounds are generally in good agreement with experimental data. The results are then utilized, along with a Penn type of single-oscillator model for the dielectric constant, to calculate the pressure coefficient of the refractive index. The results are good for elemental semiconductors and reasonable for III-V compounds. Similar calculations of pressure coefficients of both the energy gaps and the refractive index for several II-VI compounds yield results which are less satisfactory. Possible reasons for this discrepancy are discussed.
TL;DR: In this article, the magneto-stark effect and electronic transport properties on GaSe have been studied and it has been shown that GaSe has nearly isotropic electronic states at the forbidden gap and the valence band anisotropy is anomalous.
TL;DR: In this article, the surface states on the cleavage GaAs (110) were analyzed using the bond orbital model and the empty and filled bands were associated with Ga and As, respectively.
Abstract: Careful photoemission studies of surface states on the cleavage GaAs (110) detect no filled states in the band gap. However, empty states pin the surface Fermi level on n ‐type GaAs at midband gap. Filled states are placed below the valence‐band maximum and empty surface states in the upper half of the band gap. Calculations, using the bond orbital model, agree with these results and associate the empty and filled bands with Ga and As, respectively.
TL;DR: In this article, the physics of the emission of electrons from interface states in metal-insulator-semiconductor (MIS) systems, under isothermal, non-steady-state conditions, are discussed.
Abstract: The physics is discussed of the emission of electrons from interface states in metal-insulator-semiconductor (MIS) systems, under isothermal, non-steady-state conditions. Generalized equations are then derived which permit the determination of the non-steady-state, emission current vs time characteristics for MOS systems containing an arbitrary distribution of surface states; the special case of a discrete surface state is also studied. More important, however, by appropriate plotting of the data, it is shown how to directly extract from the experimental data the energy distribution and the capture cross section of the interface traps in the upper-half of the band gap in the case of n-type semiconductors, and in the lower-half of the band gap in the case of p-type semiconductors.
TL;DR: In this article, a two-valence band model was proposed for lead-salt ionic semiconductors, based on the properties of PbS, PbSe, and PbTe.
Abstract: Publisher Summary Lead salts are ionic semiconductors with many properties in common. Their IV-VI electron configuration is relatively unusual, and appears to be reflected in the interesting phonon and dielectric properties they share. Among these are low values of the TO phonon frequency at Γ and high static dielectric constants. It is clear that the electronic structures of PbS, PbSe, and PbTe are much the same, with all three lead salts exhibiting a direct minimum energy gap E 0 at the L point. The surfaces of constant energy for both electrons and holes are ellipsoidal near the band edges, but approach a cylinder-like shape farther from the L point. The conduction and valence bands in all the lead salts are definitely nonparabolic, displaying a concomitant dependence of the effective mass on carrier concentration. Based primarily on studies of PbTe, a two-valence band model is well supported by experiment. The order of higher energy bands appears quite well established, and reliable values of the energies of several interband transitions have been obtained.
TL;DR: In this paper, the absolute values of all four photoionization cross sections for electron and hole emission from the gold acceptor and donor levels in silicon have been evaluated by measuring junction photocurrents.
Abstract: The absolute values of all four photoionization cross sections for electron and hole emission from the gold acceptor and donor levels in silicon have been evaluated by measuring junction photocurrents. By using two light sources it has been shown that steady‐state photocurrents provide a unique determination of threshold energies for transitions between the energy bands and the impurity levels, independent of the type of junction. Not too far away from the threshold energies, the experimental results are in good agreement with the δ‐function impurity potential model of Lucovsky. Threshold energies of 0.555 and 0.61 eV are obtained for the electron and hole emission from the acceptor levels, respectively, and 0.75–0.83 and 0.345 eV for the corresponding emissions from the donor levels. For the acceptor levels, the sum of the threshold energies (1.165 eV) is very close to the band gap (1.166 eV), which indicates that relaxation effects are small. In addition, the influence of the valence‐band structure on the energy dependence of the photoionization cross section for the hole emission has been investigated.
TL;DR: In this article, the tunneling characteristics of Cr/SiO2/Si structures in the thickness range 23-34 A were reported and the E −κ dependence in the energy range extending 3.5 eV below the oxide conduction band was determined by the thickness dependence to be approximately of the Franz form with an effective mass ratio of 0.42.
Abstract: The tunneling characteristics of Cr/SiO2/Si structures in the thickness range 23–34 A are reported. The E‐κ dependence in the energy range extending 3.5 eV below the oxide conduction band is determined by the thickness dependence to be approximately of the Franz form with an effective mass ratio of 0.42. Tunneling into the indirect conduction band of silicon is reduced by a thickness‐independent factor which decreases approximately exponentially with the energy below the direct band edge.
TL;DR: In this paper, the relationship between the magnitude of the charge transferred and the work function difference is shown to be linear, while in the latter case it ranges from an exponential to a quadratic depending on the band bending and the energetic position of the traps.
Abstract: Metal-insulator contact charging models are presented for insulators having (a) traps uniformly distributed in the energy gap and (b) discrete traps in the energy gap. It is shown that in the former case the relationship between the magnitude of the charge transferred and the workfunction difference is linear, while in the latter case it ranges from an exponential to a quadratic depending on the band bending and the energetic position of the traps. Screening lengths are calculated for the two cases, and it is shown that the thickness of the insulator is usually not the limiting factor in contact charging, even for thin-film insulators. Finally, it is shown that the times required for the charge transfer can be short.
TL;DR: In this article, the absorption coefficient, reflection coefficient and index of refraction as a function of wavelength were determined for two light polarizations (e ∥ a and e ∥ b ).
TL;DR: In this paper, the lifetime and quantum yield of Dy3+ have been measured in perprotonated and perdeuterated dimethylsulfoxide and methylcyanide under various excitation conditions.
Abstract: The lifetime and quantum yield of fluorescence from the 4F9/2 level of Dy3+ have been measured in perprotonated and perdeuterated dimethylsulfoxide and methylcyanide under various excitation conditions. The results are compared to those obtained in light and heavy water and with other rare earth ions and discussed with reference to the modified energy gap law in the theory of radiationless transitions. The specific energy gap in Dy3+ is such that efficiency of quenching depends on matching the electronic energy gap of the ion by a single vibration of C–H, C–D, or C–N and on the distance of the bond from the ion.
TL;DR: In this article, the Boltzmann law was used to analyze the spectral changes of the charge transfer photoluminescence of the title compound between 2 and 10°K.
TL;DR: In this paper, the effect of an incremental electric field in the bulk semiconductor is deduced from a simple analytical treatment, and some qualitative features are shown for an electrostatically selfconsistent solution, initially without correlation and exchange forces, for the effect that electrons which tunnel from the metal of a Schottky barrier into the energy band gap of the semiconductor.
Abstract: Some qualitative features are shown for an electrostatically self-consistent solution, initially without correlation and exchange forces, for the effect of electrons which tunnel from the metal of a Schottky barrier into the energy band gap of the semiconductor. The effect of an incremental electric field in the bulk semiconductor is deduced from a simple analytical treatment. In covalent semiconductors most of the incremental electric field terminates in the semiconductor in a manner almost independent of the nature of the metal, i.e., the effective “metal” electrode exists inside the bulk semiconductor. This is not true for ionic semiconductors. When the “metal” electrode location is used as the origin for the image force, a normal square root of the field dependence of the Schottky image force lowering is predicted at low electric fields and a linear dependence is predicted at high electric fields, both as reported recently by Andrews. The model also predicts the order of magnitude of the very small ba...
TL;DR: In this paper, a study of the optical absorption spectrum of GaSe at the energy gap shows that the strength of the exciton line decreases as hydrostatic pressure is increased, and it is proposed that this effect comes from increasing interference of the discrete exciton lines with a continuum of structure due to indirect interband electronic transitions.
Abstract: A study of the optical absorption spectrum of GaSe at the energy gap shows that the strength of the exciton line decreases as hydrostatic pressure is increased. It is proposed that this effect comes from increasing interference of the discrete exciton line with a continuum of structure due to indirect interband electronic transitions. The sign and magnitude of the pressure coefficients of the gaps in gallium chalcogenides are found to be consistent with recent band-structure studies.
TL;DR: In this paper, Gax, In1−x Sb alloys were used for piezoreflective experiments between 77 and 300°K and Eo and Δo splitting was observed to be linear with composition.
TL;DR: In this paper, a configurational coordinate model was proposed to explain the behavior of red luminescence in CdS in terms of a configural coordinate model, and a vibrational energy of about 70% of the LO phonon energy was calculated for the excited state of the center.
Abstract: Red luminescence in CdS has been studied in as‐grown and ion‐implanted crystals An IR band consisting of two emission bands, IR1 and IR2, is produced by ion implantation The higher‐energy band, IR1, has the same origin as the R band observed in some as‐grown crystals A comparison of the R and IR1 bands in CdS with self‐activated (SA) luminescence in ZnS and GaAs shows that they are SA luminescence at 17 eV at low temperatures in CdS The temperature variations in peak energy, half‐width, and intensity of luminescence are discussed, and the behavior is explained in terms of a configurational coordinate model A vibrational energy of 0025 eV, which is about 70% of the LO phonon energy in CdS, is calculated for the excited state of the center The study of the excitation dependence of the center shows that the luminescence is due to an electronic transition within a localized center and not due to a donor‐acceptor pair recombination The center has an excitation band about 022 eV below the band gap Th