ESR STUDY OF THE EFFECT OF UNIAXIAL STRESS ON THE BAND STRUCTURE OF CdS:I

1967 ◽  
Vol 45 (1) ◽  
pp. 127-135 ◽  
Author(s):  
B. J. Slagsvold ◽  
C. F. Schwerdtfeger
Keyword(s):  
Longitudinal Strain ◽  
Optical Band Gap ◽  
Energy Gap ◽  
Uniaxial Stress ◽  
Uniaxial Pressure ◽  
Transverse Strain ◽  
Deformation Potential ◽  
Average Change ◽  
Valence Bands ◽  
G Value

The shift with uniaxial pressure in the g value of the ESR signal obtained from conductive iodine-doped CdS has been measured at ≈ 1.7 °K. For pressures parallel to the c axis, an average change in the g tensor of ≈ 9.4 × 10−7 cm2/kg was found, while for perpendicular pressures [Formula: see text] shifted an average of ≈ 4.4 × 10−7 cm2/kg. These shifts have been ascribed to a change in the energy gap separating the conduction-band minimum from the valence bands. They, as well as the change in the optical band gap with hydrostatic pressure as measured by Langer (1960), could be fairly well described by the approximate values 6.3 eV/unit longitudinal strain and 1.8 eV/unit transverse strain of the deformation potential constants for the gap.

Uniaxial Stress Effects On Valence Band Structures Of GaN

1997 ◽  
Vol 482 ◽  
Author(s):  
A. A. Yamaguchi ◽  
Y. Mochizuki ◽  
C. Sasaoka ◽  
A. Kimura ◽  
M. Nido ◽  
...  
Keyword(s):  
Valence Band ◽  
Uniaxial Stress ◽  
Reflectance Spectroscopy ◽  
Experimental Results ◽  
Energy Separation ◽  
Strain Effect ◽  
Deformation Potential ◽  
Stress Effects ◽  
Polarization Characteristics ◽  
Valence Bands

AbstractValence band modification by uniaxial stress in GaN is investigated by reflectance spectroscopy. It is observed that the energy separation between the A and B valence bands increases with the applied uniaxial stress in the c-plane. Changes of the wavefunctions by the stress are also investigated by the polarization characteristics of the reflectance spectra. The experimental results are analyzed on the basis of k•p theory, and deformation potential D5 is experimentally determined as -3.3 eV. It is indicated that the uniaxial strain effect could be utilized for improving GaN-based laser performance.

Valence Band Physics in Wurtzite GaN

1997 ◽  
Vol 468 ◽  
Author(s):  
T. Azuhata ◽  
T. Sota ◽  
S. Chichibu ◽  
A. Kuramata ◽  
K. Horino ◽  
...  
Keyword(s):  
Shear Deformation ◽  
Valence Band ◽  
Energy Gap ◽  
Free Exciton ◽  
Elastic Stiffness ◽  
Binding Energies ◽  
Deformation Potential ◽  
Orbit Splitting ◽  
Strain Dependence ◽  
Valence Bands

ABSTRACTWe present a summary of recent progress towards the understanding of the valence-band physics in wurtzite GaN. Systematic studies have been performed on the strain dependence of the free exciton resonance energies by photoreflectance measurements using well-characterized samples. Analyzing the experimental data with the Hamiltonian appropriate for the valence bands, the values have been determined of the crystal field splitting, the spin-orbit splitting, the shear deformation potential constants, and the energy gap in the unstrained crystal. Discussions are given on the strain dependence of the energy gaps, of the effective masses, and of the binding energies for the free exciton ground states as well as on the valence band parameters. Using the obtained values and the generalized Elliott formula, the fundamental optical absorption spectra obtained experimentally were analyzed. The values of the elastic stiffness constants, which play a crucial role to determine the shear deformation potential constants, are also given.

Optical Properties of Wurtzite GaN and ZnO Quantum Dots

2004 ◽  
Vol 818 ◽  
Author(s):  
Vladimir A. Fonoberov ◽  
Alexander A. Balandin
Keyword(s):  
Quantum Dots ◽  
Decay Time ◽  
Radiative Decay ◽  
State Energy ◽  
Energy Gap ◽  
Dead Layer ◽  
Bulk Gan ◽  
Piezoelectric Field ◽  
Zno Quantum Dots ◽  
Valence Bands

AbstractWe have investigated exciton states in wurtzite GaN/AlN and ZnO quantum dots. A strong piezoelectric field in GaN/AlN quantum dots is found to tilt conduction and valence bands, thus pushing the electron to the top and the hole to the bottom of the GaN/AlN quantum dot. As a result, the exciton ground state energy in GaN/AlN quantum dots with heights larger than 3 nm exhibits a red shift with respect to bulk GaN energy gap. It is shown that the radiative decay time in GaN/AlN quantum dots is large and increases from 0.3 ns for quantum dots with height 1.5 nm to 1.1×103 ns for the quantum dots with height 4.5 nm. On the contrary, the electron and the hole are not separated in ZnO quantum dots. Moreover, a relatively thick “dead layer” is formed near the surface of ZnO quantum dots. As a result, the radiative decay time in ZnO quantum dots is small and decreases from 73 ps for quantum dots with diameter 1.5 nm to 29 ps for the quantum dots with diameter 6 nm.

Deposition of Thin Films of Silicon Carbide on Fused Quartz and on Sapphire by Laser Ablation of Ceramic Silicon Carbide Targets

1992 ◽  
Vol 285 ◽  
Author(s):  
L. Rimai ◽  
R. Ager ◽  
J. Hangas ◽  
E. M. Loaothetis ◽  
Nayef Abu-ageel ◽  
...  
Keyword(s):  
Thin Films ◽  
Silicon Carbide ◽  
Room Temperature ◽  
Optical Band Gap ◽  
Energy Gap ◽  
Fused Silica ◽  
High Resistivity ◽  
Fused Quartz ◽  
Amorphous Sic ◽  
Very High

ABSTRACTAblation of ceramic silicon carbide with 351 nm excimer radiation was used to depositSIC films on fused silica and on sapphire. For deposition temperatures above 850° C, diffraction shows the films to be crystalline with the [111] axis preferentially oriented normally to the film. Optical spectra show an indirect energy gap at 2.2 eV, near that for the cubic polytype, although the 200 diffractions are absent. Room temperature resistivities range between .02 to .1 Ωcm. Deposition below 600° C yields amorphous SiC with no diffraction bands, low and variable optical band gap and very high resistivity.

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.

Photoreflectance Characterization of InGaAs Lattice Matched to InP

1993 ◽  
Vol 324 ◽  
Author(s):  
V. Bellani ◽  
M. Amiotti ◽  
M. Geddo ◽  
G. Guizzetti ◽  
G. Landgren
Keyword(s):  
Energy Gap ◽  
Lattice Mismatch ◽  
Blue Shift ◽  
X Ray Diffraction ◽  
X Ray ◽  
Different Temperatures ◽  
Interfacial Strain ◽  
Valence Bands ◽  
Lattice Matched

AbstractWe measured photoreflectance (PR) spectra at different temperatures between 80 and 300 K, and optical absorption (OA) at 3 K on MOVPE grown Inl-xGaxAs nearly lattice-matched to InP. x-ray diffraction measurements gave a lattice mismatch δa/ao = -0.9.10−3 between ternary alloy and InP, corresponding to × = 0.485. We obtained the energy gap dependence on T from PR spectra. The blue shift of the gap was accounted for in terms of compositional difference with respect to the perfectly lattice matched alloy (× = 0.472), and elastic strain; moreover PR and OA showed evidence of the valence bands splitting at k = 0 due to interfacial strain, in fine agreement with theory.

ESR STUDIES OF GMR RELATED MATERIALS I: ESR of Mn IN LaMnO3 AND La0.99Ca0.01MnO3

2000 ◽  
Vol 14 (25n26) ◽  
pp. 883-897 ◽  
Author(s):  
N. ARAI ◽  
K. SUGAWARA
Keyword(s):  
Magnetic Susceptibility ◽  
Temperature Dependence ◽  
Spin System ◽  
High Field ◽  
Energy Gap ◽  
Low Field ◽  
High Field Esr ◽  
Clear Signal ◽  
Spin Clusters ◽  
G Value

ESR measurements are carried out for La 1-x Ca x MnO 3 (x=0, 0.01) from 760 K down to 4 K. A clear signal was observed above 260 K, presumably arising from Mn 3+ and Mn 4+, but two kinds of signals, the low-field and high-field ESR with g≃2, were observed below it. The high- and low-field signals are tentatively assumed to originate from Mn 4+ and Mn 3+, respectively. The g-value, linewidth, and intensity of the high-field signal nearly follow ∝1/(T-106). The temperature dependence of g-shift of the low-field signal is similar to that of magnetic susceptibility of LaMnO 3. The ESR intensity anomalously increases at temperatures between about 150 K and 250 K, which is tentatively ascribed to the occurrence of "spin-clusters". Above ≃300 K, the ESR intensity nearly follows Curie's law, and the linewidth is proportional to exp (-500/T), an indication of some kind of energy-gap existence in the Mn spin system.

Fabrication and Characterization of RF Plasma Polymerized Thin Films from 3,7-Dimethyl-1,6-octadien-3-ol for Electronic and Biomaterial Applications

2010 ◽  
Vol 123-125 ◽  
pp. 323-326 ◽  
Author(s):  
Kateryna Bazaka ◽  
Mohan V. Jacob ◽  
Robert A. Shanks
Keyword(s):  
Thin Films ◽  
Optical Band Gap ◽  
Energy Gap ◽  
Polymer Chains ◽  
Rf Plasma ◽  
Circuit Boards ◽  
Average Roughness ◽  
Free Surfaces ◽  
Complete Dissociation

Poly(linalool) thin films were fabricated using RF plasma polymerisation. All films were found to be smooth, defect-free surfaces with average roughness of 0.44 nm. The FTIR analysis of the polymer showed a notable reduction in –OH moiety and complete dissociation of C=C unsaturation compared to the monomer, and presence of a ketone band absent from the spectrum of the monomer. Poly(linalool) were characterised by chain branching and a large quantity of short polymer chains. Films were optically transparent, with refractive index and extinction coefficient of 1.55 and 0.001 (at 500 nm) respectively, indicating a potential application as an encapsulating (protective) coating for circuit boards. The optical band gap was calculated to be 2.82 eV, which is in the semiconducting energy gap region.

Investigation of Optical Properties of ZnO/MnO2, ZnO/TiO2 and ZnO/MnO2/TiO2 Nanocomposites

2014 ◽  
Vol 938 ◽  
pp. 123-127 ◽  
Author(s):  
G. Shanmuganathan ◽  
I.B. Shameem Banu
Keyword(s):  
Optical Properties ◽  
Room Temperature ◽  
Optical Band Gap ◽  
Energy Gap ◽  
Visible Region ◽  
Solid State Reaction Method ◽  
Morphological Properties ◽  
Energy Dispersive Analysis ◽  
Reaction Method ◽  
Uv Visible

ZnO nanocomposites such as (ZnO)0.8(MnO2)0.2, (ZnO)0.8(TiO2)0.2and (ZnO)0.8(MnO2)0.1(TiO2)0.1were prepared by solid state reaction method at room temperature. The structural analysis was carried out with help of powder XRD to confirm the formation of the composites. The morphological properties and presence of elemental compositions were analyzed with scanning electron microscope and energy dispersive analysis spectroscopy respectively. Optical properties were studied with UV visible spectrophotometer. From the transmittance spectrum, it is concluded that the synthesized composite materials have the transmittance in the range of 80 to 95% in the visible region. The calculated optical band gap values for pure ZnO is 3.16 eV and the values are 3.7eV, 5.27eV and 4.46eV for the composites ZnO/MnO2, ZnO/TiO2and ZnO/MnO2/TiO2, respectively. The study has found that the ZnO/MnO2, ZnO/TiO2and ZnO/MnO2/TiO2composites have very large energy gap as that of insulator.

scholarly journals Novel Empirical Correlation Between the Optical Refractive Index and Energy Bandgap in Semiconductors: Comparative Study

2021 ◽  
Author(s):  
Hosam Mohamed Gomaa ◽  
I.S. Yahia ◽  
H.Y. Zahran
Keyword(s):  
Experimental Data ◽  
Refractive Index ◽  
Comparative Study ◽  
Optical Band Gap ◽  
Energy Gap ◽  
Theoretical Studies ◽  
Oxide Glasses ◽  
High Agreement ◽  
Different Types ◽  
Number Of Publications

Abstract This work is an attempt to review some of the most famous and important studies to correlate the optical-linear refractive index of a substance to its energy band-gap.The refractive index of different types of materials, like semiconductors, insulators, oxides, thin-films, and oxide glasses, has been reported in a large number of publications in attempts to the estimation of how it can be correlated to the optical band-gap. The present work can be considered as a comparative study between the most successful relations in correlating the refractive index to the energy gap. The careful reviewing of the previous studies to correlate the optical refractive index and energy gap led to concluded that Reddy and Ahmmed approximation was selected to develop a new realized form that can give a good fit to the experimental data and, hence, be used directly as an accurate formula in the theoretical studies. The obtained formula correlates the optical refractive index to the energy gap and the oxygen atom's electronegativity. Such relation has been used to calculate the refractive indices for more than 96 materials (elements/compounds) with a high agreement with the experimental data.

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