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.

Phonon-assisted absorption in crossed electric and magnetic fields in direct-band semiconductors. II

1969 ◽  
Vol 47 (5) ◽  
pp. 521-531 ◽  
Author(s):  
I. P. Batra
Keyword(s):  
Magnetic Fields ◽  
Optical Absorption ◽  
Electric Field ◽  
Energy Gap ◽  
Level Structure ◽  
Perturbation Expansion ◽  
Weak Electric Field ◽  
Electric And Magnetic Fields ◽  
Direct Energy ◽  
New Perturbation

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 crossed electric and magnetic fields on the optical absorption in that region of the Urbach tail where second order processes are dominant. The experimentally favorable situation involving a weak electric field is investigated. A new perturbation expansion in terms of a dimensionless parameter is developed in this connection and is used to obtain the weak electric field limit. Such a study may be useful in exploring the Landau level structure of the valence and conduction bands separately.

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 The Band-Gap Studies of Short-Period CdO/MgO Superlattices

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Ewa Przeździecka ◽  
P. Strąk ◽  
A. Wierzbicka ◽  
A. Adhikari ◽  
A. Lysak ◽  
...  
Keyword(s):  
Band Gap ◽  
Layer Thickness ◽  
Energy Gap ◽  
Band Gaps ◽  
Short Period ◽  
Wide Range ◽  
Salt Structure ◽  
Short Period Superlattices ◽  
Direct Band ◽  
Sublayer Thickness

AbstractTrends in the behavior of band gaps in short-period superlattices (SLs) composed of CdO and MgO layers were analyzed experimentally and theoretically for several thicknesses of CdO sublayers. The optical properties of the SLs were investigated by means of transmittance measurements at room temperature in the wavelength range 200–700 nm. The direct band gap of {CdO/MgO} SLs were tuned from 2.6 to 6 eV by varying the thickness of CdO from 1 to 12 monolayers while maintaining the same MgO layer thickness of 4 monolayers. Obtained values of direct and indirect band gaps are higher than those theoretically calculated by an ab initio method, but follow the same trend. X-ray measurements confirmed the presence of a rock salt structure in the SLs. Two oriented structures (111 and 100) grown on c- and r-oriented sapphire substrates were obtained. The measured lattice parameters increase with CdO layer thickness, and the experimental data are in agreement with the calculated results. This new kind of SL structure may be suitable for use in visible, UV and deep UV optoelectronics, especially because the energy gap can be precisely controlled over a wide range by modulating the sublayer thickness in the superlattices.

Optical Transitions in Chalcogenide Glasses From the Point of View of a Barrier-Cluster Model

2008 ◽  
Vol 39-40 ◽  
pp. 253-256
Author(s):  
Ivan Baník
Keyword(s):  
Optical Absorption ◽  
Low Temperatures ◽  
Cluster Model ◽  
Chalcogenide Glasses ◽  
Temperature Shift ◽  
Point Of View ◽  
Optical Transitions ◽  
Influence Of Temperature ◽  
Exponential Tails ◽  
Influence Of Temperature On

A barrier-cluster model of chalcogenide glasses is employed to analyze optical transitions near the absorption edge. The influence of temperature on the optical absorption is studied. The model is used to explain the temperature shift of exponential tails of the optical absorption and the temperature dependence of the optical forbidden-band width at low temperatures.

A Theoretical Study on the Pressure Dependence of the Band Gap in ${\rm A^{I}B^{III}C^{VI}_2}$ Compounds

1997 ◽  
Vol 11 (16) ◽  
pp. 1959-1967 ◽  
Author(s):  
R. Asokamani ◽  
R. Mercy Amirthakumari ◽  
G. Pari
Keyword(s):  
Theoretical Study ◽  
Energy Gap ◽  
Ambient Pressure ◽  
Chalcopyrite Structure ◽  
Deformation Potential ◽  
Equilibrium Lattice Constant ◽  
Self Consistent ◽  
Direct Energy ◽  
Experimental Values ◽  
Direct Energy Gap

The self-consistent scalar relativistic band structure for AgGaX 2 (X = S, Se, Te) performed in chalcopyrite structure using the TBLMTO method at various pressures are reported here. Empty spheres were introduced in the calculations as the chalcopyrite structure is loosely packed. From the total energy calculations, the equilibrium lattice constant and the bulk modulus at zero pressure were calculated and these values agree well with the reported experimental values. All these compounds are found to have direct energy gap at ambient pressure with the gap widening with increased pressures which are in agreement with the experimental results. The deformation potential, dE g /dP for the compounds are also reported here. The metallisation volumes are calculated and the possibility of observing superconductivity in these compounds is discussed.

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.

Robust Half-Metallic Character In KMnGe Half-Heusler Compound

2021 ◽  
Vol 1 (2) ◽  
pp. 9-17
Author(s):  
Chibueze T. C ◽  
Ezema F. I
Keyword(s):  
Energy Gap ◽  
Half Metallic ◽  
Spintronic Devices ◽  
Electronic Spin ◽  
Materials Research ◽  
Direct Band ◽  
Spin Injectors ◽  
Low Pressures

The search for spin injectors and spin sources in spintronic devices is a significant facet of materials research today. Consequently, half-Heusler (HAH) KMnGe alloy has been recommended as one such admissible materials. Herein, a rigorous examination of the structural, magnetic and electronic properties of HAH KMnGe alloy is done using ab initio method within the bolstered up rendition of the functional by Perdew and his group. Our result shows that HAH KmnGe alloy expresses type-1 and type-2 HAH  structural ground state at high and low pressures respectively, which may pose a challenge in application. Impressively, HAH KMnGe alloy exhibits half metallic characteristic with an indirect energy gap in the Γ-X symmetry k-point and direct band gap at X-point in the minority electronic spin states for type-1 and type-2 phase respectively. Our findings agree fundamentally with some previous findings in the literature and suggests that the HAH KMnGe alloy is a credible excellent spin source in future spintronic devices.

scholarly journals Optical Absorption Exhibits Pseudo-Direct Band Gap of Wurtzite Gallium Phosphide

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Bruno C. da Silva ◽  
Odilon D. D. Couto ◽  
Hélio T. Obata ◽  
Mauricio M. de Lima ◽  
Fábio D. Bonani ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Band Gap ◽  
Gallium Phosphide ◽  
Direct Band Gap ◽  
Direct Band
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