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.

Profiling Composition Variations in Composition-Modulated GaP/InP Short-Period Superlattices Using Resonance Raman Scattering

1999 ◽  
Vol 583 ◽  
Author(s):  
H. M. Cheong ◽  
Yong Zhang ◽  
A. G. Norman ◽  
J. D. Perkins ◽  
A. Mascarenhas ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Band Gap ◽  
Resonance Raman ◽  
Band Gap Energy ◽  
Resonance Raman Scattering ◽  
Rich Region ◽  
Gap Energy ◽  
Composition Modulation ◽  
Short Period ◽  
Short Period Superlattices

AbstractWe use resonance Raman scattering (RRS) and electroreflection (ER) measurements to profile the the composition and strain variations in laterally composition-modulated (CM) GaP/InP short-period superlattices (SPS's). The ER spectra of a GaP2.2/InP2.0 SPS give the fundamental band-gap energy at 1.69±0.05eV, which is about 210 meV lower than the band gap energy of a GaInP random alloy with the same overall composition. The RRS measurements reveal strong dependences of the phonon spectrum on the polarization and the excitation energy. In RRS spectra measured with the polarization of both excitation and scattered photons along the composition modulation direction, the GaP-like longitudinal optical (LO) phonon redshifts by 4.0±0.5 cm−1 near the resonance with the fundamental energy gap. On the other hand, when the polarizations are orthogonal to the composition modulation, the LO phonons redshift as much as 16 cm−1 at low excitation energies. A comparison of the experimental data with a model calculation gives the average In composition in the In-rich region as 0.70±0.02, and the average Ga composition in the Ga-rich region as 0.68±0.02. Our result also indicates that there are small volumes (less than 1% volume fraction) with very high In mole fraction.

Influence of Structural Parameters to Engineer the Band Gaps in Ternary Pnictide Semiconductors - Theory as a Tool

2007 ◽  
Vol 124-126 ◽  
pp. 57-60 ◽  
Author(s):  
Rita John
Keyword(s):  
Band Gap ◽  
Energy Gap ◽  
Structural Parameters ◽  
Tight Binding ◽  
Band Gaps ◽  
Theoretical Tool ◽  
Linear Muffin Tin Orbital

The band gap anomaly exhibited by ABC2 : A = Cd; B = Si,Ge,Sn; C = P,As pnictides with respect to their binary analogs GaP, Ga0.5In0.5P, InP, GaAs, Ga0.5In0.5As, InAs is studied using Tight Binding Linear Muffin Tin Orbital (TBLMTO) method as an investigating theoretical tool. The influence of the structural parameters, η and u are analyzed to enable one to tune energy gap to make tailor made compounds.

Characterization of ultrathin Ge epilayers on (100) Si

1991 ◽  
Vol 69 (3-4) ◽  
pp. 246-254 ◽  
Author(s):  
J. -M. Baribeau ◽  
D. J. Lockwood ◽  
T. E. Jackman ◽  
P. Aebi ◽  
T. Tyliszczak ◽  
...  
Keyword(s):  
Strain Relaxation ◽  
Three Dimensional ◽  
Raman Scattering Spectroscopy ◽  
X Ray ◽  
Transmission Electron ◽  
Short Period ◽  
Short Period Superlattices ◽  
Direct Band ◽  
X Ray Absorption

The understanding of the epitaxy of pure Ge layers on Si is an important step towards the synthesis of SimGen (m, n < 10 monolayers) short-period superlattices. The possibility of a direct band-gap character makes these structures extremely attractive. We have grown thin buried Gen ([Formula: see text] monolayers) films on (100) Si by molecular beam epitaxy and studied their structural properties by a variety of techniques including Raman scattering spectroscopy, glancing incidence X-ray reflection, Rutherford backscattering, transmission electron microscopy, and extended X-ray absorption fine structure analysis. All these techniques allowed detection of the thin Ge layers and provided information about the thickness, morphology, strain distribution, and interface sharpness of these heterostructures. The Ge„ films with [Formula: see text] had a two-dimensional nature and showed no sign of strain relaxation. Intermixing at the Si–Ge interfaces was present in all these films and estimated to be not more than two monolayers. This smearing at the interfaces may have contributed to the maintenance of that pseudomorphicity. A thicker Ge layer (n = 12) showed evidence of strain relaxation and clustering in three-dimensional islands.

The effect of the blocking of impact ocean waves by the crevasse-ridden ice shelf

2020 ◽  
Author(s):  
Yuri Konovalov
Keyword(s):  
Band Gap ◽  
Numerical Experiments ◽  
Amplitude Spectrum ◽  
Ocean Waves ◽  
Band Gaps ◽  
Elastic Model ◽  
Ice Shelf ◽  
Impact Wave ◽  
Wide Range ◽  
The Impact

&lt;p&gt;The propagation of high-frequency elastic-flexural waves through an ice shelf was modeled by a full 3-D elastic model, which also takes into account sub-ice seawater flow. The sea water flow is described by the wave equation. Numerical experiments were undertaken both for an intact ice shelf free of crevasses, which has idealized rectangular geometry, and for a crevasse-ridden ice shelf. The crevasses were modeled as triangle/rectangular notches into the ice shelf. The obtained dispersion spectra (the dispersion curves describing the wavenumber/periodicity relation) are not continuous. The spectra reveal gaps that provide the transition from n-th mode to (n+1)-th mode. These gaps are observed both for an intact ice shelf free of crevasses and for a crevasse-ridden ice shelf. They are aligned with the minimums in the amplitude spectrum. That is the ice shelf essentially blocks the impact wave at this transition. However, the dispersion spectrum obtained for a crevasse-ridden ice shelf, has a qualitatively difference from that obtained for an intact ice shelf free of crevasses. Moreover, the dispersion spectrum obtained for a crevasse-ridden ice shelf reveals the band gap &amp;#8211; the zone there no eigenmodes exist (Freed-Brown and others, 2012). The numerical experiments with the crevasse-ridden ice tongue that is 16 km in longitudinal extent, 0.8km width and 100m thick, were undertaken for a wide range of the periodicities of the incident wave: from 5 s to 250 s. The obtained dispersion spectra reveal two band gaps in this range: the first band gap at about 20 s and the second band gap at about 7 s for 1km spatial periodicity of the crevasses. The width of the band gap significantly increases when the crevasses depth increases too. Respectively, the amplitude spectra reveal significantly increasing area of periodicities/frequencies where the ice shelf blocks the impact wave.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Freed-Brown, J., Amundson, J., MacAyeal, D., &amp; Zhang, W. (2012). Blocking a wave: Frequency band gaps in ice shelves with periodic crevasses. Annals of Glaciology, 53(60), 85-89. doi:10.3189/2012AoG60A120&lt;/p&gt;&lt;p&gt;Konovalov, Y.V. (2019). Ice-shelf vibrations modeled by a full 3-D elastic model. Annals of Glaciology, 1-7. doi:10.1017/aog.2019.9&lt;/p&gt;

Composition-dependent band gaps and indirect–direct band gap transitions of group-IV semiconductor alloys

2015 ◽  
Vol 17 (33) ◽  
pp. 21605-21610 ◽  
Author(s):  
Zhen Zhu ◽  
Jiamin Xiao ◽  
Haibin Sun ◽  
Yue Hu ◽  
Ronggen Cao ◽  
...  
Keyword(s):  
Band Gap ◽  
Transition Point ◽  
Reliable Method ◽  
Group Iv ◽  
Band Gaps ◽  
Semiconductor Alloys ◽  
Direct Band Gap ◽  
Group Iv Semiconductor ◽  
Direct Band

Obtaining the value of the band gap and the composition of an indirect–direct band gap transition point for group-IV semiconductor alloys by an efficient and reliable method.

Simulation of InAsSb/InGaAs Quantum Dots for Optical Device Applications

2004 ◽  
Vol 851 ◽  
Author(s):  
Paul von Allmen ◽  
Seungwon Lee ◽  
Fabiano Oyafuso
Keyword(s):  
Quantum Dots ◽  
Electronic Structure ◽  
Band Gap ◽  
Atmospheric Chemistry ◽  
Energy Gap ◽  
Tight Binding ◽  
Atomic Interaction ◽  
Optical Detectors ◽  
Wide Range ◽  
Device Applications

ABSTRACTSelf-assembled InAsSb/InGaAs quantum dots are candidates for optical detectors and emitters in the 2–5 micron band with a wide range of applications for atmospheric chemistry studies. It is known that while the energy band gap of unstrained bulk InAs1−xSbx is smallest for x=0.62, the biaxial strain for bulk InAs1−xSbx grown on In0.53Ga0.47As shifts the energy gap to higher energies and the smallest band gap is reached for x=0.51. The aim of the present study is to examine how the electronic confinement in the quantum dots modifies these simple considerations. We have calculated the electronic structure of lens shaped InAs1−xSbx quantum dots with diameter 37 nm and height 4 nm embedded in a In0.53Ga0.47As matrix of thickness 7 nm and lattice matched to an InP buffer. The relaxed atomic positions were determined by minimizing the elastic energy obtained from a valence force field description of the inter-atomic interaction. The electronic structure was calculated with an empirical tight binding approach. For Sb concentrations larger than x=0.5, it is found that the InSb/ In0.53Ga0.47As heterostructure becomes type II leading to no electron confined in the dot. It is also found that the energy gap decreases with increasing Sb content in contradiction with previous experimental results. A possible explanation is a significant variation is quantum dot size with Sb content.

Photoelectrochemical properties of n-type KTaO3 single crystals in alkaline electrolytes

2010 ◽  
Vol 25 (1) ◽  
pp. 52-62 ◽  
Author(s):  
Irene E. Paulauskas ◽  
Gerald E. Jellison ◽  
Lynn A. Boatner
Keyword(s):  
Band Gap ◽  
Single Crystals ◽  
Model Potential ◽  
Water Dissociation ◽  
Transition Metal Atoms ◽  
Wide Range ◽  
Alkaline Electrolytes ◽  
Direct Band ◽  
Indirect Band Gap ◽  
External Quantum Yield

Semiconducting KTaO3 single crystals were investigated as a model potential photoanode for hydrogen production using photoelectrochemical cells. To modify the electronic properties of KTaO3 by reducing the band gap and thereby increasing the absorption of light at longer wavelengths, the crystals were doped during growth. A wide range of dopant elements was used that consisted primarily of transition metal atoms. Most of the crystals exhibited n-type behavior with carrier concentrations from 4 × 1018 to 2.6 × 1020 cm–3. The position of the band edges indicated that the crystals were thermodynamically capable of water dissociation. External quantum yield measurements revealed that the samples were photoactive up to a wavelength of ∼350 nm. The indirect band gap and a parameter denoted as E1 that is related to the direct band edge of the semiconductor, were found to be essentially the same for all of the samples. These results indicate that the various dopants and treatments did not produce changes in the KTaO3 electronic structure that were sufficient to significantly modify the behavior of KTaO3 in a PEC cell.

Direct gap Group IV semiconductors for next generation Si-based IR photonics

2014 ◽  
Vol 1666 ◽  
Author(s):  
John Kouvetakis ◽  
James Gallagher ◽  
José Menéndez
Keyword(s):  
Band Gap ◽  
Lattice Parameter ◽  
Group Iv ◽  
Optical Data ◽  
Long Wavelength ◽  
Group Iv Semiconductors ◽  
Wide Range ◽  
Direct Band ◽  
Ternary Semiconductor ◽  
Group Iv Elements

ABSTRACTThis paper presents synthesis and optical properties of mono-crystalline Ge1-ySny and Ge1-x-ySixSny semiconductor alloys grown on Si/Ge platforms via purposely designed CVD routes using highly reactive Si/Ge/Sn hydrides including Ge3H8, Ge4H10, Si4H10 and SnD4. The Ge1-ySny materials are shown to exhibit strong and tunable photoluminescence induced by the substitution of sizable Sn concentrations in the Ge diamond lattice ultimately leading to an indirect-to-direct band gap crossover at y= 0.08-0.09. The optical data indicate that the IR coverage of the alloy extends well beyond that of elemental Ge into the broader long wavelength range suggesting a variety of applications in Si-based photonics. Ge1-x-ySixSny alloys represent the first viable ternary semiconductor among group IV elements with independently tunable lattice parameter and electronic structure. Studies of the compositional dependence of direct and indirect edges in these alloys using photoluminescence and photocurrent measurements are reviewed. The optical results show band gap variation over a wide range above and below that of Ge from 1.1 to 0.5 eV and provide the first demonstration of direct gap behavior in this semiconductor system.

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