Equilibrium distributions of misfit dislocation density along the growth direction of metamorphic buffer layers In
x
Al
1–
x
As/GaAs with maximum In content
x
max
> 0.77 and different non-linear ...graded composition profiles
are calculated. The effect of the initial In composition (
n =
2) of In
x
Al
1–
x
As buffer layer with convex-graded (
x
min
) composition profile on misfit dislocation density as well as amount of residual stresses at its top part is considered. Using computational approach, it was shown that a dislocation-free region is formed under thin tensile- strained GaAs layer (1–10 nm) inserted into InAlAs metamorphic buffer layer, which agrees with experimental data obtained early by transmission electron microscopy. Novel non-linear graded composition profile of metamorphic buffer layer has been proposed, which results in twice reduction of misfit dislocation density as compared to the convex-graded one. In addition, equilibrium distributions of misfit dislocation density in the HEMT heterostructures with two-dimensional electron channel In
x
Al
1–
x
As, which are based on In
0
.
75
Ga
0
.
25
As/In
0
.
75
Al
0
.
25
As metamorphic buffer layer of various designs, are calculated. The values of inverse steps (
A
), representing the difference between the maximum In content of In
x
Al
1–
x
As (
x
max
) and In content of In
0
.
75
Al
0
.
25
As virtual substrate, at which relaxation of the elastic strains in 2D channel In
0
.
75
Ga
0
.
25
As/In
0
.
75
Al
0
.
25
As doesn’t occur, are calculated for metamorphic buffer layers In
x
Al
1–
x
As with convex-graded and optimized non-linear graded composition profiles.
In the present paper we study magneto-intersubband oscillations (MISO) in HgTe/Hg1−xCdxTe single quantum well with "inverted" and "normal" spectra and in In1−xGaxAs/In1−yAlyAs quantum wells with ...normal band ordering. For all the cases when two branches of the spectrum arise due to spin-orbit splitting, the mutual arrangement of the antinodes of the Shubnikov-de Haas oscillations and the maxima of MISO occurs opposite to that observed in double quantum wells and in wide quantum wells with two subbands occupied and does not agree with the theoretical predictions. A "toy" model is proposed that explains qualitatively this unusual result.
•Non-linear graded InAlAs buffer is proposed for efficient dislocation reduction.•Metamorphic InAlAs/GaAs structures with optimized graded buffer were grown by MBE.•Impact of highly strained 2–10 nm ...GaAs layer on dislocation density was studied.•No elastic strains relaxation in virtual substrate at inverse step value < 0.04.•1,5 times reduction of dislocation density in structure with proposed buffer.
Metamorphic InxAl1-xAs (xmax > 0.75) buffer layer (MBL) grown on GaAs with an optimized non-linear graded composition profile along the growth direction is proposed for enhanced reduction of misfit dislocation (MD) density in highly mismatched III-V/GaAs metamorphic heterostructures. The equilibrium distributions of MD density throughout such InxAl1-xAs/GaAs MBLs are calculated. The influence of the initial composition (xmin) of MBL and the elastically strained thin GaAs layer embedded into the InxAl1-xAs MBL on the MD density distribution was studied. An optimum value of the inverse step (Δ), representing the difference between the top In content of the InxAl1-xAs MBL and that of a In0.75Al0.25As virtual substrate (VS) grown atop is determined. It was theoretically shown that Δ above 0.04 results in relaxation of the elastic stresses in VS via formation of the MDs, while the lower Δ values allow growing the VS completely free of MDs. Finally, the metamorphic In0.75Al0.25As/graded-InAlAs/GaAs heterostructures differing from each other by only the composition profile of the graded-InAlAs MBL were grown by MBE on GaAs(001) and studied by atomic force microscopy. The structure with proposed optimized non-linear graded (x = 0.05–0.77) MBL demonstrated the ∼ 1.5 times less MD density as compared to that with the convex-graded (x = 0.05–0.81) MBL, which was estimated to be at the level of ∼ 2·107 cm−2.
High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5 μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in ...particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1 Å are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ∼8 μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic InxAl1-xAs buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded InxAl1-xAs MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6 μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T = 10–300 K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As4/III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3 × 107 cm−2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300 nm, the extremely low surface roughness with the RMS value of 1.6–2.4 nm, measured by AFM, as well as rather high 3.5 μm-PL intensity at temperatures up to 300 K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform.
We studied the effects of single and combined action of protons and carbon ions
12
C
6+
on the pool of MCF-7 human breast cancer stem cells. Single irradiation with a beam of protons or carbon ions ...had no significant effects on the relative number of cancer stem cells (CSC). The effects of combined irradiation in a total equieffective dose of 4 Gy depended on the sequence of exposure to ionizing radiations: the relative number of CSC did not change after irradiation with carbon ions and then with protons, but increased in the case of the reverse sequence. The most favorable result,
i.e
. a decrease in the CSC pool, was observed in the case of sequential irradiation with carbon ions and protons and their equal contribution to total equieffective dose. In this case, the absolute number of CSC decreased by on average 2.1 times in comparison with the control (
p
<0.05). The revealed regularities are of interest for the further development of new methods of radiation therapy.
Gas and dust clouding after large-scale blasting at Sitovo Quarry in the Lipetsk Region and the resultant pollution of the neighborhoods of the nearest towns is studied. The concentrations of solid ...particles less than 2.5
m in size are determined in real time using modern equipment. The electronic filming of a large-scale blast and the dust cloud transfer with the wind within the limits of the quarry allowed considering a theoretical partial problem on propagation of fine-dispersion dust from the upper portion of the cloud from a height of 50–100 m to the recording points on ground surface beyond the quarry limits. The methods of computational fluid dynamics are used to model flow at the bottom of the atmospheric boundary layer disturbed by the wind interaction with the quarry topography. It is shown that turbulent diffusion ensures vertical dispersion of micro particles down to the recording points. An explanation is proposed for the revealed non-monotonic maximal concentration of dust over ground surface with an increasing distance from the quarry.
This paper reports the results of satellite image and seismological data analysis obtained when considering the causes of a landslide on the Yelbashinskii dump at the Kolyvan anthracite deposit. The ...potential for determining the natural vibrations of large objects from low-frequency seismological records and monitoring thereof has been demonstrated.
We report on a comparative study of the elastic strain relaxation in InAs(Sb)/In(Ga,Al)As heterostructures grown by molecular beam epitaxy on GaAs substrates via InAlAs metamorphic buffer layer (MBL) ...with and without a highly strained 5 nm-thick GaAs insertion. Reflection high energy electron diffraction was used for in situ monitoring an in-plane lattice parameter of the epitaxial layers during growth. As a result, critical thickness of the initial stage of the InAlAs metamorphic buffer layer as well as its corresponding composition were determined for the structures with different position of the GaAs insertion within the MBL. The structure with 5 nm-thick GaAs layer inserted in the InAlAs MBL directly after achieving the In content of 37 mol.% demonstrates the highest room temperature photoluminescence at a wavelength of about 3.5 μm.
Formation and sintering of nanostructured Al
2
O
3
and boehmite powders prepared by hydrothermal synthesis from aluminum powder are studied. Formation of workpieces (green bodies) is performed by ...extrusion, static and explosive pressing followed by high-temperature sintering. Use of explosive pressing increases raw material density, reduces the temperature for α-Al
2
O
3
formation, activates sintering, and improves ceramic operating properties.
This study discusses the problem of increasing the accuracy of contact conductometers. This study also describes the main sources of error in the primary measuring transducer of a contact ...conductometer, which include the solution resistance, polarization resistance, and capacitance of the double electric layer and the characterization of the electrochemical processes on the primary measuring transducer electrodes. Moreover, this study presents the methods for determining the specific parameters that affect the impedance of the primary measuring transducer. Method 1 is based on the analysis of the amplitude–frequency characteristics of the active component of the impedance of the conductive cell of a contact conductometer filled with a solution. Method 2 is based on the determination of the active component of the impedance of the solution at the resonance frequency, i.e., at zero reactive components of the impedance. In Method 3, the active component of the impedance of the solution is determined at three different frequencies. Results showed that Method 2 can only reliably determine the active resistance of the solution. The cell constants are determined by Methods 1 and 3 in the same frequency range. Meanwhile, Method 2 uses a frequency that is several times higher than the upper limit of the frequency range. Notably, the cell constants determined by Methods 2 and 3 practically coincide with each other and significantly differ from the cell constants determined by Method 1.
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