Showing papers on "Band gap published in 1973"
TL;DR: In this paper, the optical absorption spectra of amorphous and crystalline thin Wo3 films have been measured in the temperature range 110° to 500°K and the temperature coefficient of the band edges was found to be − 5.0 × 10−4 eV/°K.
Abstract: Thin films of Wo3 deposited on quartz substrates at room temperature have been shown to be amorphous in structure. The optical absorption spectra of the amorphous and crystalline films have been measured in the temperature range 110° to 500°K. The fundamental absorption edge of an amorphous film occurs at 3800 A which on crystallization moves to 4500 A. On the high-energy side of the absorption edge several absorption peaks are resolvable in both types of film. The frequency dependence of the absorption coefficient below 104 cm−1 is described by an expression of the form K (v, T) = K 0 exp[− (β/kT) (E 0 − hv)] and above 104 cm−1 it follows a square law dependency. The temperature coefficient of the band edges was found to be − 5.0 × 10−4 eV/°K and the estimated band gaps at 0°K were found to be 3.65 and 3.27 eV for the amorphous and crystalline films, respectively. The electrical conductivity of a thin film has been measured in the temperature range 298–573°K and the activation energy was found t...
933 citations
TL;DR: In this paper, the energy band gaps for elemental and binary compound semiconductors and insulators were tabulated for 723 references and the determinations believed to be the most reliable were indicated.
Abstract: Energy band gaps are tabulated for elemental and binary compound semiconductors and insulators reported in 723 references. The method of measurement, transition, type of sample, and other pertinent information are included for each entry. The determinations believed to be the most reliable are indicated.
592 citations
TL;DR: In this article, singlecrystal layers of AlN have been grown on sapphire substrates between 1000 and 1100 °C by vapor phase reaction of aluminum chlorides with ammonia, and the purity, color, crystallinity, growth morphology, and electrical resistivity of the epitaxial layers have been investigated.
Abstract: Single‐crystal layers of AlN have been grown on sapphire substrates between 1000 and 1100 °C by vapor‐phase reaction of aluminum chlorides with ammonia. The purity, color, crystallinity, growth morphology, and electrical resistivity of the epitaxial layers have been investigated. Infrared specular reflection measurements showed the presence of an appreciable strain at the AlN‐sapphire epitaxy interface. Optical absorption data strongly suggest the AlN is a direct band‐gap material with a value of about 6.2 eV at room temperature.
525 citations
TL;DR: In this article, it was shown that reduced critical fields, entropies, and specific heats of superconductors, regardless of coupling strength, can be fitted essentially within experimental errors by curves appropriate to a system of independent fermion quasiparticles.
Abstract: We show that reduced critical fields, entropies, and specific heats of superconductors, regardless of “coupling-strength,” can be fitted essentially within experimental errors by curves appropriate to a system of independent fermion quasiparticles. The analysis proceeds from the formula for the entropy of a system of independent fermionsS=−k
B
Σ [f lnf+(1−f) ln (1−f)], where we take the quasiparticle spectrum to be the same as in the BCS (weak-coupling) theoryE
2
=(e
2
+Δ2). The temperature dependence of the energy gap is also taken to be the same as in the BCS theory, the only adjustable parameter being the gap ratio Δ(0)/k
B
T
c
. The necessary values of this ratio are found to be in reasonable agreement with the experimental values deduced from electron tunneling and infrared absorption. Some speculations are offered for the paradoxical success of this simple model, based on analogies with the effects of strong coupling in the normal state.
324 citations
TL;DR: In this paper, the ground-state energies of electron-hole metals were calculated using Hubbard's approximate treatment of the electron gas for the following cases: (a) germanium, (b) GHE with a large (111) strain, (c) silicon, and (d) GaAs.
Abstract: In this paper the energetics of the formation of electron-hole metallic liquids in semiconductors is examined. The ground-state energies of electron-hole metals are calculated using Hubbard's approximate treatment of the electron gas for the following cases: (a) germanium, (b) germanium with a large (111) strain, (c) silicon, and (d) GaAs. The simple case of a single isotropic maximum for the valence band and a single minimum for the conduction band is also treated. It is shown that for both Si and Ge, the binding energy of the metallic state relative to free excitons is 5.7 and 1.7 meV, respectively. These values and the values of the equilibrium density are in good agreement with experiment. In the isotropic model the metallic state is not bound while for GaAs and strained Ge the metallic-state energy per electron is essentially equal to that for a gas of free excitons. The low-density limit of the isotropic band model is examined and the ground state for this system is predicted to be a dilute gas of molecules. It is argued that the forces between molecules are repulsive and will cause this state to break up at relatively low densities. If the density is increased, the system will undergo a first-order transition to the metallic state. The relevance of these calculations to the metal-insulator transition problem is discussed. It is pointed out that the fact that anisotropic and many-valleyed bands favor the metallic state means that the metal-insulator transition must ultimately be first order.
298 citations
TL;DR: In this article, the general transport equations in a heavy doped semiconductor are given, taking the position-dependent band structure into account, and an intrinsic concentration depending on the doping levels is introduced.
Abstract: The general transport equations in a heavy doped semiconductor are given, taking the position-dependent band structure into account. An intrinsic concentration depending on the doping levels is introduced. This quantity allows us to use the classical equations in a slightly modified form, if Maxwell-Boltzmann statistics can be applied for one or both kinds of the carrier. The total density of states in a heavy doped semiconductor is assumed to be the envelope of the density of states of the conduction (valence) band and impurity band. The effect of the skewness of the impurity band is included. The Fermi level and the effective intrinsic carrier concentration are calculated for this total density of states function. Experimental evidence for the calculated values is given.
263 citations
176 citations
TL;DR: In this article, the authors investigated the mechanism of laser-induced reversible refractive index damage in LiNbO3 and LiTaO3 with a view to elucidating the mechanism.
Abstract: The properties of Fe2+, Fe3+, and other 3dn ionic impurities in the LiNbO3 structure are investigated with a view to elucidating the mechanism of laser‐induced reversible refractive index damage. Polarized optical absorption spectra of Fe2+ in LiNbO3 and LiTaO3 are reported and interpreted. The 2.66 eV band responsible for laser damage in Fe‐doped LiNbO3 is identified as Fe2+ → Nb5+ intervalence transfer. The Fe d e level lies in the 3.7 eV band gap at about 0.6 eV below the conduction band, and the activation energy for thermal Fe2+ → Nb5+ electron transfer is estimated to be about 0.9 eV, in reasonable agreement with the value of 1.3 ± 0.2 eV observed for thermal bleaching of Fe2+ centers in x‐irradiated LiNbO3. Particular advantages of intervalence transfer as a mechanism for initiating optical index damage are noted. The observed electric field gradients in pure LiNbO3 and LiTaO3 are related to the B20 ligand‐field parameter of a 3dn (n ≠ 5) impurity ion. Comparison with experimental estimates of B20 ...
163 citations
TL;DR: In this article, the authors derived selection rules for the direct optical valence-to-conduction band transitions in GaSe near the fundamental gap using pseudopotential band calculations.
Abstract: Absorption, and reflexion spectra of GaSe near the fundamental gap are interpreted in terms of pseudopotential band calculations. Selection rules for the direct optical valence-to-conduction band transitions are derived. Valence band mixing induced by spin-orbit coupling is invoked to explain the low observed probability for transitions in light polarized perpendicular to the crystal c-axis. The spectra of the excitons associated with the direct gap are discussed in the ellipsoidal effectivemass approximation. Corrective terms are added to account for the observed exchange splitting of the exciton ground state. Field-free spectra as well as spectra modified by the presence of magnetic fields parallel and perpendicular to c are considered. The magneto-Stark effect which gives rise to a mixing of the 2s and2py states and thus renders the2py state visible affords determination of the anisotropy parameter. The value of this parameter as well as those of the components parallel and perpendicular to c of the reduced effective masses show that the electronic states in GaSe are nearly isotropic. This is in good agreement with the results of the pseudopotential band calculations which clearly demonstrate the three-dimensional character of valence and conduction bands.
145 citations
TL;DR: In this article, the authors developed a theory for thermally stimulated currents (TSC) that flow in optically or electrically excited insulators and semiconductors in which the field is sufficiently high and the active region in which free carriers are generated is sufficiently thin (e.g., reverse-biased junctions, thin films, etc.) so that recombination rate of the free carriers is negligible.
Abstract: The theory is developed for thermally stimulated currents (TSC) that flow in optically or electrically excited insulators and semiconductors in which the field is sufficiently high and the (active) region in which the free carriers are generated is sufficiently thin (e.g., reverse-biased junctions, thin films, etc.) so that recombination rate of the free carriers is negligible. Closed-form solutions are obtained for the TSC characteristics for semiconductors and insulators containing arbitrary trap distributions. Using various ad hoc trapping distributions, it is shown that the approximate high-field TSC characteristics correlate extremely well with the exact characteristics that were computed numerically. More important, however, it is shown that the shape of the observed TSC characteristic is a direct reflection of the sum of the trap distribution in the upper half and the lower half of the band gap. The technique is potentially a powerful means of characterizing trap distributions in defect semiconductors and insulators, in that it permits the direct determination of the trap distribution without requiring an a priori knowledge of the trap parameters and without the need for laborious analyses.
137 citations
TL;DR: In this paper, the authors used photoluminescence excitation spectra to derive accurate values for the lowest indirect and direct excitonic band gaps of the "exotic" compounds AlAs and AlP.
Abstract: The measurement of photoluminescence excitation spectra is shown to be a powerful method to obtain information on the lower fundamental energy gaps in materials where suitable samples for transmission measurements cannot readily be prepared. In this work this method is used to derive accurate values for the lowest indirect and direct excitonic band gaps of the "exotic" compounds AlAs and AlP. The indirect ${\ensuremath{\Gamma}}_{15v}\ensuremath{-}{X}_{1c}$ excitonic edge was found as 2.229 \ifmmode\pm\else\textpm\fi{} 0.001 eV at 4 K, 2.223 \ifmmode\pm\else\textpm\fi{} 0.001 eV at 77 K and 2.153 \ifmmode\pm\else\textpm\fi{} 0.002 eV at 300 K. The $X$-point phonon energies observed for AlAs are ${E}_{\mathrm{LO}(X)}$, 50.0 \ifmmode\pm\else\textpm\fi{} 1.0 meV; ${E}_{\mathrm{TO}(X)}$, 41.5 \ifmmode\pm\else\textpm\fi{} 1.0 meV; ${E}_{\mathrm{LA}(X)}$, 27.5 \ifmmode\pm\else\textpm\fi{} 1.5 meV; and ${E}_{\mathrm{TA}(X)}$, 13.5 \ifmmode\pm\else\textpm\fi{} 1.0 meV, giving an $X$-point deviation from the Brout sum rule ${\ensuremath{\Delta}}_{K}(X)=0.09$ for AlAs. The lowest direct ${\ensuremath{\Gamma}}_{15c}\ensuremath{-}{\ensuremath{\Gamma}}_{1c}$ excitonic edge in AlAs was found to vary from 3.13 \ifmmode\pm\else\textpm\fi{} 0.01 eV at 4 K to 3.03 \ifmmode\pm\else\textpm\fi{} 0.01 eV at 300 K. For AlP, the corresponding values found experimentally for excitonic band gaps are 2.505 \ifmmode\pm\else\textpm\fi{} 0.01 eV at 4 K for the indirect ${\ensuremath{\Gamma}}_{15v}\ensuremath{-}{X}_{1c}$ transition and 3.63 \ifmmode\pm\else\textpm\fi{} 0.02 eV at 4 K for the lowest direct gap (probably ${\ensuremath{\Gamma}}_{15v}\ensuremath{-}{\ensuremath{\Gamma}}_{1c}$).
TL;DR: In this paper, the intrinsic electron-hole band gap was used to explain photoemission and photoconduction of polyethylene in the photon energy range 7
Abstract: Intrinsic photoemission and photoconduction of polyethylene in the photon energy range 7
TL;DR: In this paper, measurements of the differential capacitance of evaporated gold Schottky barriers on laboratory-grown, boron-doped semiconducting diamonds have been obtained for the first time as functions of reverse-bias voltage, frequency, and temperature.
Abstract: Measurements of the differential capacitance of evaporated gold Schottky barriers on laboratory-grown, boron-doped semiconducting diamonds have been obtained for the first time as functions of reverse-bias voltage, frequency, and temperature The data are analyzed on the basis of a model which includes the effects of long time constants for hole capture from the deep (boron) level, as well as previously unobserved effects due to the series resistance of the bulk The barrier height at 300°K is found to be 1·73 ± 1·10 eV , in good agreement with the ‘one-third band gap’ value of Mead and Spitzer Excellent correlation is found between optical transmission measurements and the C-V analysis for the uncompensated boron concentration, indicating that all of the optically observable dopant is electrically active By fitting the model with two adjustable parameters at room temperature, good agreement is obtained between measured and calculated capacitance over two and a half decades as a function of temperature The analysis indicates that the activation energy of the acceptor level is 0·26–0·37 eV for the samples studied, while the associated capture cross-sections are 0·9–2·0 × 10 −17 cm 2
TL;DR: In this paper, the density of states, including critical point assignments and band structures, were computed using the empirical pseudopotential method for Si, Ge, GaAs, InSb, GaP, ZnSe, and CdTe.
Abstract: Density-of-states calculations are presented based on band structures computed using the empirical pseudopotential method. Data from recent measurements of x-ray photoemission spectra and ultraviolet photoemission spectra are used to obtain the theoretical parameters. It was necessary to include a nonlocal pseudopotential to obtain consistency with experiment. Results for the density of states, including critical-point assignments and band structures, are given for Si, Ge, GaAs, InSb, GaP, ZnSe, and CdTe.
TL;DR: In this article, the valence band structure of representative MX2 layer structure compounds has been obtained by X-ray photoemission with monochromatized radiation, and the results were compared with u.v. and He II photo-emission and with recent band structure calculations.
TL;DR: In this paper, a galvanic cell is used to detect the electrochemical potential of Ag +, since the interdiffusion of Cu + into AgI is nearly forbidden except near Cu 2 Se.
Abstract: The phase diagram is studied by X-ray and thermal analyses. The high temperature phase (α) is the solid solution of b.c.c. or f.c.c. in which Ag + , Cu + and electron are mobile. The galvanic cell Ag|AgI|specimen|Pt is available to controle the excess or deficit Ag density and to detect the electrochemical potential of Ag + , since the interdiffusion of Cu + into AgI is nearly forbidden except near Cu 2 Se. With the help of the cell and utilizing the weight-difference between Ag and Cu, the polarization and the interdiffusion are measured and interpreted with the diffusion theory. The electronic and ionic conductivities are measured with varying temperature and x . Further the various properties of α(Ag, Cu) 2 Se such as the conductivity, Hall coefficient, thermoelectric power, thermal conductivity etc. are measured and compared with the theory, indicating that the energy gap decreases with increasing x .
TL;DR: In this paper, the effect of disorder-induced valence-conduction band mixing on the conduction-band effective mass in small-band-gap III-V alloys has been analyzed.
Abstract: The conduction-band effective mass in small-band-gap III-V alloys has been observed to be heavier than would be expected from a standard $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}$ calculation in the virtual-crystal approximation. Here we analyze the effect of disorder-induced valence-conduction band mixing on this effective mass. It is found that with a consistent set of assumptions for interband and intraband mixing, one can account for the variation of the band gap, the spin-orbit splitting, and the conduction-band mass in these alloys.
TL;DR: In this article, a metal is placed upon the surface of a semiconductor and the resulting changes in the electron interaction near the interface produce changes in exchange and correlation potential, and the most important aspect is that the potential changes differ with the state considered.
Abstract: For pt. I see abstr. A75119 of 1972. When a metal is placed upon the surface of a semiconductor the resulting changes in the electron interaction near the interface produce changes in the exchange and correlation potential. The most important aspect is that the potential changes differ with the state considered. In particular the reaction of the valence and conduction bands are very different causing changes in the band gap in the surface region. The image potential has opposite signs in the valence and conduction band corresponding to the semiclassical electron and hole picture; this is shown to be due to the screened exchange difference between the two bands. The screened exchange difference between the two bands is calculated numerically up to the surface for the two limiting cases of a covalent and ionic semiconductor. Finally the difference in behaviour of these two types is briefly discussed in the light of the results on Schottky barriers.
TL;DR: In this paper, the results of the energy band structure calculations of A2B4C25 compounds are reviewed, and the differences in the energy spectra passing from A3B5 semiconductors to their closest ternary analogs are described.
TL;DR: In this paper, a review of the analysis of the energy band structure of I-III-VI 2 semiconductors is presented, where the presence of noble metal d levels in the valence band has been confirmed directly by the observation of electroreflectance structure due to transitions from the d levels themselves to the lowest conduction band minimum.
TL;DR: In this paper, the authors measured emission spectra, excitation spectra and intensity dependence of the luminescence, decay of the luminance, and temperature dependence of ZnO emission at 1·70 eV.
TL;DR: In this paper, the optical energy gap and the lattice parameters of ZnSxTe1-x have been measured, and the energy gap bowing is compared with previous theoretical estimates.
Abstract: Thin films of ZnSxTe1-x have been grown in the composition range 0
TL;DR: In this article, the ionization energy for alpha particles and electrons were measured in two high purity silicon guard ring detectors between 100 K and 250 K. The measured values of? in electron volts per hole pair (eV/ehp) are: Ee- = 975.2 keV E? = 5483,?e- (300 K) = 3.631,?e-(100 K), etc.
Abstract: High precision absolute measurements of the ionization energy (?) for alpha particles and electrons have been made in two thick high purity silicon guard ring detectors between 100 K and 250 K. At a fixed energy (E) both ?? and ?e- were found to vary linearly (r = 0.999) with the band gap (WG). ?? and ?e- also increased with E and ?e- ? ??. The slope (??a/?WG) = 1.83 ± 0.04 is the lowest so far reported and is in closer agreement with Drummond and Moll's theoretical value of 1.73. However (?e-/?WG) = 2.87 ± 0.07 is significantly higher. The measured values of ? in electron volts per hole pair (eV/ehp) are: Ee- = 975.2 keV E? = 5483 Kev ?e- (300 K) = 3.631 ?? (300 K) = 3.625 ?e-(100 K) = 3.745 ?? (100 K) = 3.698 The estimated probable error is ± 0.0025 eV/ehp. The ?? values are close to other recent published results. These results taken in conjunction with earlier reported work on Si, Ge, GaAs and CdTe suggest that (??/?WG)? 1.8 in all these semiconductors, i.e. over the WG range from 0.7 to 1.6 eV. Therefore there is a need for further ? measurements on high purity samples of all four materials.
TL;DR: In this article, the one-band effective mass approximation for the dispersion relationship in the barrier of a metal-insulator-metal (MIM) tunnel junction fails if the barrier height is a considerable portion of the band gap of the insulator.
Abstract: The one‐band effective mass approximation for the dispersion relationship in the barrier of a metal‐insulator‐metal (MIM) tunnel junction fails if the barrier height is a considerable portion of the band gap of the insulator. This paper reports on results when the more realistic dispersion relation of Franz and Kane is used and displays the sensitivity of the tunnel effect to the band model. We illustrate some examples of the energy distribution of the current. Characteristic features of tunneling through trapezoidal‐like barriers will be discussed, including maxima in the logarithmic derivative curves, in the thermal I‐V characteristics, and the zero‐bias offset of the conductance minimum. Calculations are performed by integrating the tunnel equation numerically, and analytical approximations for this equation are also presented from which the effect of various parameters on the tunneling characteristic can be estimated.
TL;DR: In this paper, the true optical bandgap of CdTe between many conflicting results was determined: E g = 1.529 meV with a temperature coefficient of −3.10 −4 eV/°K.
TL;DR: In this paper, the average energy to create an electron-hole pair, Ex, is given essentially by ℏ ωp/n, where ω p is the plasmon energy and n is the number of pairs which are created by the plasmons and its decay products.
Abstract: Fast electrons in solids lose energy primarily to plasmons which subsequently decay into an electron‐hole pair. The electron and hole may create additional electron‐hole pairs if they have sufficient energy. The average energy to create an electron‐hole pair, Ex, is thus given essentially by ℏ ωp/n, where ℏ ωp is the plasmon energy and n is the number of pairs which are created by the plasmon and its decay products. The values of n and hence Ex depend on the ratio ℏωp/Eg, where Eg is the usual band gap in semiconductors and insulators. We have found that for a simple model of direct and indirect materials, sharp thresholds exist for various values of n. For direct‐gap materials, n=1 for 1< ℏωp/Eg<4, n=3 for 4< ℏωp/Eg<12, etc. Similar relations for indirect‐gap materials have also been obtained. Consideration of phonon losses, effective masses, and problems with k conservation indicate that the changes in n vs ℏωp/Eg should be smoothed for real materials. but not eliminated. Our theoretical values for Ex/E...
Journal Article•
TL;DR: In this paper, the binding mechanisms by which isoelectronic impurities may produce bound states in the forbidden energy gap of semiconductors are investigated with a method based on the pseudopotential approach to the band structure.
TL;DR: In this article, the principal optical constants of the germanium telluride (GeTe) system have been obtained by inverting the spectra using the Kramers-Kronig technique.
Abstract: The reflectance spectra of bulk samples of the germanium telluride (GeTe) system have been measured in the wavelength range 13 to 0.2 μm. The principal optical constants of the system have been obtained by inverting the spectra using the Kramers-Kronig technique. Two distinct types of behavior were encountered depending on whether or not a sample exhibited a free carrier absorption peak. Samples rich in germanium lacked such a peak and had optical properties very similar to amorphous GeTe films. Tellurium rich samples always showed a large free carrier peak and from analysis of their optical Constants the effective mass and optical energy gap of the system was obtained. The variation of the effective mass and energy gap with composition (i.e., hole carrier density) is consistent with the existence of two sets of valence-conduction bands in the system. A multiple band model based on experimental and theoretical data is outlined and its parameters are found to be in good agreement with published work.