ENERGY-GAP VARIATION IN MIXED III–V ALLOYS

1967 ◽  
Vol 45 (2) ◽  
pp. 255-261 ◽  
Author(s):  
A. G. Thompson ◽  
J. C. Woolley
Keyword(s):  
Optical Absorption ◽  
Mole Fraction ◽  
Energy Gap ◽  
Optical Transition ◽  
Empirical Relation ◽  
Energy Gaps ◽  
Direct Optical Transition ◽  
Crystal Type ◽  
The Mean ◽  
Alloy Systems

Values of E0, the lowest direct optical transition, are available for several III-V alloy systems, from measurements of optical absorption, electroreflectance, electroluminescence, etc. It is shown that in all available cases the variation of E0 with composition can be fitted very well to an equation of the form E0 = A + Bx + Cx2, where x is the mole fraction of one component compound. Such a relation is expected from a virtual-crystal type of analysis.If E0m is the mean of the energy gaps of the component compounds of the system, it is found that an empirical relation of the form [Formula: see text] appears to hold where α is approximately 0.3 eV3/2.

scholarly journals Theoretical study of strain-dependent optical absorption in a doped self-assembled InAs/InGaAs/GaAs/AlGaAs quantum dot

2018 ◽  
Vol 9 ◽  
pp. 1075-1084
Author(s):  
Tarek A Ameen ◽  
Hesameddin Ilatikhameneh ◽  
Archana Tankasala ◽  
Yuling Hsueh ◽  
James Charles ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Optical Absorption ◽  
Quantum Dot ◽  
Mole Fraction ◽  
Theoretical Study ◽  
Energy Gap ◽  
Optical Transition ◽  
Binding Model ◽  
Self Assembled ◽  
Absorption Wavelength

A detailed theoretical study of the optical absorption in doped self-assembled quantum dots is presented. A rigorous atomistic strain model as well as a sophisticated 20-band tight-binding model are used to ensure accurate prediction of the single particle states in these devices. We also show that for doped quantum dots, many-particle configuration interaction is also critical to accurately capture the optical transitions of the system. The sophisticated models presented in this work reproduce the experimental results for both undoped and doped quantum dot systems. The effects of alloy mole fraction of the strain controlling layer and quantum dot dimensions are discussed. Increasing the mole fraction of the strain controlling layer leads to a lower energy gap and a larger absorption wavelength. Surprisingly, the absorption wavelength is highly sensitive to the changes in the diameter, but almost insensitive to the changes in dot height. This behavior is explained by a detailed sensitivity analysis of different factors affecting the optical transition energy.

Sulphur-selenium compounds

1969 ◽  
Vol 22 (11) ◽  
pp. 2301 ◽  
Author(s):  
CR Ailwood ◽  
PE Fielding
Keyword(s):  
Optical Absorption ◽  
Absorption Edge ◽  
Mass Spectra ◽  
Optical Transition ◽  
Optical Absorption Edge ◽  
X Ray Diffraction ◽  
Selenium Compounds ◽  
X Ray ◽  
Direct Optical Transition

The characterization of various mixtures obtained by fractional recrystallization of sulphur-selenium melts is described. Optical absorption spectra of thin films, mass spectra, and X-ray diffraction data reveal two distinct ranges of homogeneity, the break occurring at 14 at. % Se. The optical absorption edge of crystals containing less than 14 at. % Se varies linearly with composition. A direct optical transition to the conduction band of S8 and a transition due to trapped excitons are thought to contribute to the excessive width of this absorption edge.

PHONON-ASSISTED MAGNETO ABSORPTION IN DIRECT-BAND SEMICONDUCTORS

1967 ◽  
Vol 45 (10) ◽  
pp. 3401-3410 ◽  
Author(s):  
I. P. Batra ◽  
R. R. Haering
Keyword(s):  
Optical Absorption ◽  
Energy Gap ◽  
Level Structure ◽  
Interband Absorption ◽  
Optical Transitions ◽  
Optical Phonons ◽  
Energy Gaps ◽  
Direct Energy ◽  
Direct Band ◽  
Absorption Tail

In polar semiconductors with direct energy gaps, optical absorption is observed for photons with energies well below that corresponding to the energy gap. It is now established that the absorption tail (Urbach's law) is due to indirect phonon-assisted optical transitions involving the absorption of one or more optical phonons of energy kθ. In the present paper we have considered the effect of a magnetic field on the optical absorption in that region of the Urbach tail where second-order processes are dominant. In contrast to the normal direct interband absorption coefficient, the absorption reflects the Landau level structure of valence band and conduction band separately. A discussion is given of the conditions under which such an effect should be observable.

Temperature dependence of the energy gap in superconducting Al–Al2O3–Al tunnel junctions

1968 ◽  
Vol 46 (2) ◽  
pp. 141-145 ◽  
Author(s):  
B. L. Blackford ◽  
R. H. March
Keyword(s):  
Temperature Dependence ◽  
Energy Gap ◽  
Tunnel Junctions ◽  
Small Deviation ◽  
Mean Value ◽  
Bcs Theory ◽  
Energy Gaps ◽  
The Mean ◽  
Gap Values

The most detailed measurements of the energy gap in Al by the tunneling technique have been made using Al–Al2O3-Pb junctions. Determination of the energy gaps from the I–V curves of these junctions is more precise than previous results using Al–Al2O3–Al tunnel junctions. The chief difficulty with the Al–Al2O3–Al junctions has been the lack of definition in the I–V curves, especially near Tc. Al–Al2O3–Al junctions, in which the energy-gap voltages can be read from the I-V curve with very little ambiguity up to T/Tc ≈ 0.99, are reported here. For the majority of the junctions studied, the temperature dependence of the normalized gap Δ(t)/Δ(0) shows very little scatter (T = 0.34 °K to T = Tc) and agrees closely with the BCS theory. However, a consistent small deviation is observed, with the measured gap values being slightly higher than the BCS prediction. The mean value of 2Δ(0)/kBTc obtained from 21 different junctions is 3.53 with an r.m.s. deviation of ± 0.02.

The influence of pH on the synthesis of mixed Fe-Mn oxide minerals

Clay Minerals ◽  
1990 ◽  
Vol 25 (4) ◽  
pp. 507-518 ◽  
Author(s):  
M. H. Ebinger ◽  
D. G. Schulze
Keyword(s):  
Iron Oxides ◽  
Mole Fraction ◽  
Unit Cell ◽  
Mn Oxide ◽  
Cell Dimensions ◽  
The Mean ◽  
Mn Substitution ◽  
Oxide Minerals ◽  
Unit Cell Dimensions ◽  
Influence Of Ph

AbstractMn-substituted iron oxides were synthesized at pH 4, 6, 8, and 10 from Fe-Mn systems with Mn mole fractions (Mn/(Mn + Fe)) of 0, 0·2, 0·4, 0·6, 0·8, and 1·0, and kept at 50°C for 40 days. The Mn mole fraction in goethite was <0·07 at pH 4 but increased to ∼0.47 at pH 6. Goethite and/or hematite formed in Fe and Fe + Mn syntheses at pH 4 and pH 6 at Mn mole fractions ≤0·8, and at Mn mole fractions ≤0·2 at pH 8 and pH 10. Hausmannite and jacobsite formed at pH 8 and pH 10 at Mn mole fractions ≥0·4. In the pure Mn syntheses, manganite (γ-MnOOH) formed at pH 4 and pH 6, whereas hausmannite (Mn3O4) formed at pH 8 and pH 10. As the Mn substitution increased, the unit-cell dimensions of goethite shifted toward those of groutite, and the mean crystallite dimensions of goethite decreased.

Experiments on the flow of heat in liquid helium below 0.7 °K

1958 ◽  
Vol 246 (1246) ◽  
pp. 390-405 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Liquid Helium ◽  
Free Path ◽  
Empirical Relation ◽  
Mean Free Path ◽  
Series Of Experiments ◽  
The Mean ◽  
Set Up ◽  
Low Pressures ◽  
Measured Thermal Conductivity

A series of experiments has been performed to study the steady flow of heat in liquid helium in tubes of diameter 0.05 to 1.0 cm at temperatures between 0.25 and 0.7 °K. The results are interpreted in terms of the flow of a gas of phonons, in which the mean free path λ varies with temperature, and may be either greater or less than the diameter of the tube d . When λ ≫ d the flow is limited by the scattering of the phonons at the walls, and the effect of the surface has been studied, but when λ ≪ d viscous flow is set up in which the measured thermal conductivity is increased above that for wall scattering. This behaviour is very similar to that observed in the flow of gases at low pressures, and by applying kinetic theory to the problem it can be shown that the mean free path of the phonons characterizing viscosity can be expressed by the empirical relation λ = 3.8 x 10 -3 T -4.3 cm. This result is inconsistent with the temperature dependence of λ as T -9 predicted theoretically by Landau & Khalatnikov (1949).

scholarly journals Pulse Radiolysis Studies of Collisional Deexcitation of Ne(3P1) by H2

2015 ◽  
Vol 19 (1) ◽  
pp. 75-78
Author(s):  
Deba Bahadur Khadka
Keyword(s):  
Optical Absorption ◽  
Absorption Spectroscopy ◽  
Cross Sections ◽  
Pulse Radiolysis ◽  
Science And Technology ◽  
Optical Absorption Spectroscopy ◽  
Time Resolved ◽  
Collisional Energy ◽  
The Mean ◽  
Collisional Deexcitation

The cross sections for the deexcitation of Ne(3P1) by H2 have been measured as a function of the mean collisional energy in the range of 17.3-37.9 meV or in the temperature range from 134 K to 293 K using a pulse radiolysis method as combined with time-resolved optical absorption spectroscopy. The deexcitation cross sections are in the range of 2.1- 5.6 Å2 for Ne(3P1) and nearly constant or increase slightly with increasing the collisional energy.Journal of Institute of Science and Technology, 2014, 19(1): 75-78

scholarly journals Empirical Relation for Electronic and Optical Properties of Binary Tetrahedral Semiconductors

2021 ◽  
Keyword(s):  
Dielectric Constant ◽  
Optical Properties ◽  
Atomic Number ◽  
Energy Gap ◽  
Empirical Relation ◽  
Average Energy ◽  
Optical Parameters ◽  
Dielectric Analysis ◽  
Average Atomic Number ◽  
Tetrahedral Semiconductors

The concept of ionicity has been developed by Phillips and Van Vechten from the dielectric analysis of the semiconductors and insulators to evaluate various bond parameters of binary tetrahedral (AIIBVI and AIIIBV) semiconductors. In this paper, an advance hypothesis of average atomic number of the elements in a compound has been used to evaluate intrinsic electronic and optical parameters such as ionic gap (Ec), average energy gap (Eg), crystal ionicity (fi) and dielectric constant (ϵ) of binary tetrahedral semiconductors.

Selective 4H-SiC UV Detectors

2013 ◽  
Vol 740-742 ◽  
pp. 1014-1017
Author(s):  
Evgenia V. Kalinina ◽  
O. Konstantinov ◽  
A.A. Lebedev ◽  
Yu. Gol’dberg
Keyword(s):  
Quantum Efficiency ◽  
Uv Radiation ◽  
Wavelength Range ◽  
Optical Transition ◽  
Human Beings ◽  
Radiation Level ◽  
Uv Detectors ◽  
Uv Photodetectors ◽  
Oncological Diseases ◽  
Direct Optical Transition

Carcinogenic (bactericidal) radiation (λ = 200–300 nm with a peak at 254 nm) is present in natural (Sun) and artificial (lamps) source of UV radiation. Its intensity is very low as compared to other types of radiation, but it strongly affects the health of human beings. To prevent oncological diseases, it is important to monitor the carcinogenic radiation level; i.e., selective photodetectors are required. A UV photodetectors based on n-4H-SiC Schottly barriers and p+-n junctions are proposed. The quantum efficiency spectrum of such detectors is very close to the spectrum of relative action of carcinogenic radiation on human beings due to the direct optical transition at 4.9 eV in 4H-SiC. The quantum efficiency (at the spectral peak 254 nm) amounts to about 0.3 electrons/photon for virtually zero sensitivity in other spectral regions. Quantum efficiency in the wavelength range 247–254 nm is practically independent of temperature in the range from −100 to +300°C.

Point-contact spectroscopy probing the NbSe3 CDW gap in different crystallographic orientations

2002 ◽  
Vol 12 (9) ◽  
pp. 119-122
Author(s):  
A. A. Sinchenko ◽  
P. Monceau
Keyword(s):  
Magnetic Field ◽  
Low Temperature ◽  
Applied Magnetic Field ◽  
Energy Gap ◽  
Point Contact ◽  
Point Contacts ◽  
Energy Gaps ◽  
Current Voltage ◽  
Current Voltage Characteristics ◽  
Crystallographic Orientations

We have measured the differential current-voltage characteristics of normal metal-NbSe3 direct point contacts (without insulating barrier) formed along different crystallographic orientations under applied magnetic field with different orientations. At low temperature two energy gaps, $\Delta_{p1}$ and $\Delta_{p2}$, corresponding to the high and the low-temperature CDW were observed simultaneously as a singulanty of the excess resistance which is attributed to an analog of Andreev reflection, in which the incident electron reflects on the Peierls energy gap barriers with its charge unchanged. An applied magnetic field up to 8.5 T does not lead to a change in the density of states and in the Peierls energy gaps, suggesting that the large magnetoresistance observed in NbSe3 might not result from the change in the CDW order parameter with magnetic field but rather from the increase of scattering of non-condensed to CDW carriers.

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