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1
Content available remote

Anomalous Behavior of the Hall Effect in III-V Heterostructures

100%
Dziuba Z., Górska M., Marczewski J., Przesławski T., Regiński K.
Acta Physica Polonica A
|
2000
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vol. 97
|
issue 2
331-336
EN
The Hall effect and magnetoresistance were measured in the InAs/GaAs heterostructure at temperatures from 300 K down to 3 K, in a magnetic field range from 0.01 to 1.5 T. The anomalous magnetic field dependence of the Hall coefficient in the InAs/GaAs heterostructure in magnetic fields below 0.1 T was explained as due to an extraordinary Hall effect caused by skew scattering on dislocations.
2
Content available remote

Numerical Simulations of Glide Dislocations in Persistent Slip Band

80%
Kolář M., Beneš M., Kratochvíl J., Pauš P.
Acta Physica Polonica A
|
2015
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vol. 128
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issue 4
506-509
EN
For the purpose of estimation of possible inaccuracy in standard discrete dislocation dynamics simulations, we study the motion of interacting dislocations in two regimes: the standard stress control and the total strain control. For demonstration of the difference, we consider two dislocations of opposite signs, gliding in parallel slip planes in a channel of a persistent slip band. Exposed to the applied stress, the dislocations move, bow out, and form a dipole. We investigate the passing stress needed for the dislocations to escape each from other, considering the stress controlled regime and the total strain controlled regime. The motion is described by the mean curvature flow and treated by means of the direct (parametric) method. The results of numerical experiments indicate that the stress control and the total strain control provide upper and lower estimate of the passing stress, respectively, and that these two estimates differ by approximately 10%.
3
Content available remote

High Resolution X-ray Reciprocal Space Mapping

80%
Bauer G., Li J., Holy V.
Acta Physica Polonica A
|
1996
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vol. 89
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issue 2
115-127
EN
A survey will be given on recent advances in the investigation of semiconductor epilayers, heterostructures and superlattices using reciprocal space mapping techniques based on triple-axis diffractometry. It is shown that X-ray reciprocal space mapping yields quantitative information on strain, strain relaxation, as well as composition in such structures. These data are obtained from analyses of the isointensity contours of scattered X-ray intensity around reciprocal lattice points. Further analysis of the diffuse scattering yields also information on defect distribution in the epilayers.
4
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Observation of the Coulomb Blockade at 77 K in a Lattice-Mismatched GaAs/Si Heterojunction

80%
Figielski T., Wosiński T., Mąkosa A., Riesz F.
Acta Physica Polonica A
|
1997
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vol. 92
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issue 4
745-748
EN
We investigated current-voltage characteristics of a lattice-mismatched GaAs(n)/Si(p) heterojunction. For low bias voltages at 77 K it exhibits a behaviour characteristic of the Coulomb blockade. We discuss why this unexpected phenomenon can occur in the investigated structures.
5
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Simulation of Dislocation Annihilation by Cross-Slip

80%
Pauš P., Beneš M., Kratochvíl J.
Acta Physica Polonica A
|
2012
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vol. 122
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issue 3
509-511
EN
This contribution deals with the numerical simulation of dislocation dynamics, their interaction, merging and changes in the dislocation topology. The glide dislocations are represented by parametrically described curves moving in slip planes. The simulation model is based on the numerical solution of the dislocation motion law belonging to the class of curvature driven curve dynamics. We focus on the simulation of the cross-slip of two dislocation curves where each curve evolves in a different slip plane. The dislocations evolve, under their mutual interaction and under some external force, towards each other and at a certain time their evolution continues outside slip planes. During this evolution the dislocations merge by the cross-slip occurs. As a result, there will be two dislocations evolving in three planes, two planes, and one plane where cross-slip occurred. The goal of our work is to simulate the motion of the dislocations and to determine the conditions under which the cross-slip occurs. The simulation of the dislocation evolution and merging is performed by improved parametric approach and numerical stability is enhanced by the tangential redistribution of the discretization points.
6
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Work Hardening of Magnesium Single Crystals Deformed to Stage~B at Room Temperature

80%
Sułkowski B., Mikułowski B.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
528-531
EN
Magnesium single crystals of purity (99.8 wt%) deformed to stage B on the work-hardening curve at the temperature of 293 K and at a strain rate of 10^{-3} s^{-1} were investigated. The modified Bridgman method was used to obtain the crystals of the preferred orientation of (0001)〈11\overline{2}0〉 as primary slip system. By using the method based on the experimental gradient matrix, the activity of slip systems was obtained in magnesium single crystals deformed to shear strain 1.2 γ, where well developed stage B of work hardening was observed. It was shown that primary (0001)〈11\overline{2}0〉 slip system was dominant in the whole investigated range of the examined deformation. The observation and analysis of etch pits on the {\overline{1}2\overline{1}0} plane showed the heterogeneous distribution of dislocations formed during deformation into walls of dislocations perpendicular to the (0001) slip plane. The suggested model of work hardening of magnesium single crystals, which is worth taking into consideration, shows the influence of the long-range stress field derivating from the groups of dislocations arranged in dislocation walls.
7
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3D Discrete Dislocation Dynamics Applied to Interactions between Dislocation Walls and Particles

80%
Záležák T., Dlouhý A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
450-452
EN
A 3D discrete dislocation dynamics model is presented that describes dislocation processes in crystals subjected to mechanical loadings at high temperatures. Smooth and curved dislocations are approximated by a set of short straight line segments. A Peach-Koehler force acting upon each segment involves all segment-to-segment interactions and externally applied stress. The segment velocity is a product of a corresponding mobility and the glide or climb component of the Peach-Koehler force. The model addresses interactions between dislocations and rigid spherical precipitates. A migration of low angle tilt boundaries situated in a field of precipitates is simulated as an example. The numerical implementation exploits symmetries of the model that yield an optimized and highly efficient numerical code. Results provide detailed insight into how dislocation arrangements surmount particle fields in 3D crystals.
8
Content available remote

Image Force Effect on the Separation of Partial Dislocations in Bicrystals of Hexagonal Structure Zn-Tl and Zn-Be

80%
Ayadi A., Khalfallah O.
Acta Physica Polonica A
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2013
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vol. 123
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issue 2
302-303
EN
We study the elastic interaction between a pair of partial dislocations, resulting from the dissociation of a perfect dislocation, and a bimetallic interface. The forces that act on two partials dislocations are the forces due to elastic interaction between the partial and image forces due to interactions of partial dislocations with interface. We are interested in the effect of image force on width of the stacking fault ribbon between two Schockley partials. We show that the separation of two partials dislocations is modified compared to that in the single crystal. It depends on the ratio of shear modulus and the distance between the interface and the dislocation.
9
Content available remote

Deep-Level Defects in MBE-Grown GaN-Based Laser Structure

80%
Tsarova T., Wosiński T., Mąkosa A., Skierbiszewski C., Grzegory I., Perlin P.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
331-337
EN
We present results of deep-level transient spectroscopy investigations of defects in a GaN-based heterostructure of a blue-violet laser diode, grown by plasma-assisted molecular beam epitaxy on a bulk GaN substrate. Three majority-carrier traps, T1 at E_C - 0.28 eV, T2 at E_C - 0.60 eV, and T3 at E_V + 0.33 eV, were revealed in deep-level transient spectra measured under reverse-bias conditions. On the other hand, deep-level transient spectroscopy measurements performed under injection conditions, revealed one minority-carrier trap, T4, with the activation energy of 0.20 eV. The three majority-carrier traps were revealed in the spectra measured under different reverse-bias conditions, suggesting that they are present in various parts of the laser-diode heterostructure. In addition, these traps represent different charge-carrier capture behaviours. The T1 trap, which exhibits logarithmic capture kinetics, is tentatively attributed to electron states of dislocations in the n-type wave-guiding layer of the structure. In contrast, the T2, T3, and T4 traps display exponential capture kinetics and are assigned to point defects.
10
Content available remote

3D Discrete Dislocation Dynamics: Influence of Segment Mobility on Critical Shear Stress

80%
Záležák T., Dlouhý A.
Acta Physica Polonica A
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2015
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vol. 128
|
issue 4
654-656
EN
We use 3D discrete dislocation dynamics technique to study a low-angle tilt boundary migration subjected to applied shear stress at high temperatures, where diffusion significantly contributes to the dislocation motion. The model considers Peach-Koehler forces due to interactions between individual straight dislocation segments. The model also addresses dislocation plasticity in a field of impenetrable incoherent spherical precipitates. Velocities of the individual dislocation segments are calculated in relation to the crystallography of the material. Several calculation series have been carried out for different velocity and driving force relations. The results show that there exists a critical applied shear stress, below which the low angle dislocation boundary cannot surpass the rigid precipitates and remains in an equilibrium configuration. This agrees with experimental results obtained in creep tests of dispersion strengthened alloys. The critical stresses have been calculated also for situations where the applied stress was decreased during the interaction between the low-angle tilt boundary and the precipitates.
11
Content available remote

Si_{1-x}Ge_{x} Single Crystals Grown by the Czochralski Method: Defects and Electrical Properties

80%
Argunova T., Je J., Kostina L., Rozhkov A., Grekhov I.
Acta Physica Polonica A
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2013
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vol. 124
|
issue 2
239-243
EN
Defects in Si_{1-x}Ge_{x} single crystals (2-8.5 at.% Ge) grown by the Czochralski method are investigated by synchrotron white beam topography and phase contrast imaging techniques. As the Ge concentration increases, dislocation structure evolves from individual dislocations to slip bands and sub-grain boundaries. We discuss the effect of dislocations on the electrical characteristics such as resistivity ρ_{v}, the Hall hole mobility μ_{p} and carrier lifetime τ_{e}. Diodes are fabricated by bonding p-Si_{1-x}Ge_{x} to n-Si wafers to investigate I-V characteristics and reverse recovery process. I-V characteristics are not deteriorated in spite of a five times decrease in τ_{e} with Ge concentration. A small reverse recovery time (determined by the accumulated charge) can be achieved for an optimised preset Ge concentration.
12
Content available remote

Native Deep-Level Defects in MBE-Grown p-Type CdTe

80%
Olender K., Wosiński T., Mąkosa A., Dłużewski P., Kolkovsky V., Karczewski G.
Acta Physica Polonica A
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2011
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vol. 120
|
issue 5
946-949
EN
Deep-level transient spectroscopy was used to study the defect levels in p-type CdTe layers grown by the molecular-beam epitaxy technique on lattice-mismatched GaAs substrates. In our measurements we have observed five hole traps. Two of the traps, displaying exponential capture kinetics, have been assigned to native point defects, the Cd vacancy and a complex formed of Cd vacancy and Te antisite, produced in the CdTe layers during their growth. The other two traps have been attributed to electronic states of threading dislocations on the ground of their logarithmic capture kinetics. The last trap, which was observed only when the investigated space charge region was close to the metal-semiconductor interface, has been ascribed to surface states.
13
Content available remote

Conventional and Synchrotron X-Ray Topography of Defects in the Core Region of SrLaGaO_4

80%
Malinowska A., Lefeld-Sosnowska M., Wieteska K., Wierzchowski W., Pajączkowska A., Graeff W.
Acta Physica Polonica A
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2008
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vol. 114
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issue 2
433-438
EN
SrLaGaO_4 single crystals are perspective substrate materials for high temperature superconductors thin films, elements of thermal radiation receivers and other electronic devices. The defect structure of the Czochralski grown SrLaGaO_4 crystal was investigated by means of X-ray topography exploring both conventional and synchrotron sources. The crystal lattice defects in the core region of the crystal were investigated. The regular network of defects arranged in rows only in ⟨100⟩ direction was observed. Owing to high resolution of synchrotron radiation white beam back reflection topographs one can distinguish individual spots forming the lines of the rows. It can be supposed that these elongated rod-like volume defects are located in 100 lattice planes forming a kind of walls. They are built approximately of the same phase as crystal but crystallize at a different moment than a rest of the crystal due to the constitutional supercooling.
14
Content available remote

Deep-Level Defects at Lattice-Mismatched GaAsSb/GaAs Interface

80%
Wosiński T., Mąkosa A., Raczyńska J.
Acta Physica Polonica A
|
1995
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vol. 87
|
issue 2
369-372
EN
Lattice-mismatch-induced defects were studied by means of deep-level transient spectroscopy in high-purity GaAs_{1-x}Sb_{x} layers (x = O to 3%) grown by liquid phase epitaxy on GaAs substrates. Microscopic nature and formation mechanism of two electron traps and two hole traps, which ap­peared in the layers as a result of Sb incorporation into the crystal lattice, are briefly discussed.
15
Content available remote

Numerical Simulation of Dislocation Cross-Slip with Annihilation in Non-Symmetric Configuration

80%
Pauš P., Beneš M., Kratochvíl J.
Acta Physica Polonica A
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2015
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vol. 128
|
issue 4
737-739
EN
The interpretation of the experimentally determined critical distance of the screw dislocation annihilation in persistent slip bands is still an open question. We attempt to analyze this problem using the discrete dislocation dynamics simulations. Dislocations are represented by parametrically described curves. The model is based on the numerical solution of the dislocation motion law belonging to the class of curvature driven curve dynamics. We focus on the simulation of the cross-slip of one edge dislocation curve bowing out of the wall of a persistent slip band channel and one screw dislocation gliding through the channel. The dislocations move under their mutual interaction, the line tension and the applied stress. A cross-slip leads to annihilation of the dipolar parts. In the changed topology each dislocation evolves in two slip planes and the plane where cross-slip occurred. The goal of our work is to develop and test suitable mathematical and physical model of the situation. The results are subject to comparison with symmetric configuration of two screw dislocations studied in papers by Pauš et al. The simulation of the dislocation evolution and merging is performed by the improved parametric approach. Numerical stability is enhanced by the tangential redistribution of the discretization points.
16
Content available remote

Electric-Elastic Field Induced by a Straight Dislocation in One-Dimensional Quasicrystals

80%
Yang L., Gao Y., Pan E., Waksmanski N.
Acta Physica Polonica A
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2014
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vol. 126
|
issue 2
467-470
EN
By using the generalized Stroh formalism, the electric-elastic field induced by a straight dislocation parallel to a periodic axis of a one-dimensional quasicrystal is obtained. The derivation is concise and the solution is in an exact closed form. As an illustration, the electric-elastic fields around a straight dislocation in a one-dimensional hexagonal quasicrystal are studied. Besides the interesting numerical results presented, the generalized Stroh formalism can be applied to more complicated dislocation problems in quasicrystals.
17
Content available remote

Phason Contribution to the Dislocation Loop Bias in Quasicrystals

80%
Lavrova G., Turkin A., Bakai A.
Acta Physica Polonica A
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2014
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vol. 126
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issue 2
505-507
EN
We develop a model of the absorption of vacancies and self-interstitial atoms by dislocation loops and associated phason defects in quasicrystals under irradiation. The capture efficiency and the bias of the loop for radiation point defects are evaluated for variable loop sizes. Numerical calculation of these quantities is performed for comparison. It is shown that phason defects decrease the total bias of the dislocation loop in a quasicrystal.
18
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Raman Spectroscopy for the Analysis οf Temperature-Dependent Plastic Relaxation οf SiGe Layers

70%
Pezzoli F., Bonera E., Bollani M., Sanguinetti S., Grilli E., Guzzi M., Isella G., Chrastina D., von Känel H.
Acta Physica Polonica A
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2009
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vol. 116
|
issue 1
78-80
EN
Novel architectures for electronics and photonics are expected to be developed using the forthcoming Si_{1-x}Ge_{x} technology. However, in Si_{1-x}Ge_{x}-based heterostructures, materials and design issues rely on accurate control of strain and composition of the alloy. The Raman spectroscopy has rapidly emerged as a reliable technique for the quantitative determination of such parameters on a sub-micrometric scale. In this work we present an investigation of the effects of the growth conditions of Si_{1-x}Ge_{x} graded layers on dislocation nucleation and interaction. In particular, we focus on the crucial role the deposition temperature plays in the dislocation kinetics. The analysis of threading dislocation densities is accompanied by a quantitative measurement of the residual strain in Si_{1-x}Ge_{x}/Si heterostructures, carried out by means of the Raman scattering. Our approach is effective in studying the physical mechanism governing dislocation multiplication and the sharp transition from a state of brittleness to a state of ductility within a narrow temperature window.
19
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Microstructure and Mechanical Properties of Severely Deformed AX41 Magnesium Alloy

70%
Krajňák T., Máthis K., Gubicza J., Stráská J., Janeček M.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
768-771
EN
The object of the present paper is the study of mechanical properties and microstructural evolution of AX41 magnesium alloy, severely deformed using a combination of hot extrusion and equal channel angular pressing. Equal channel angular pressing processing was performed at 250°C following route Bc. Mechanical properties of the ultrafine-grained alloy were investigated in tension at a constant strain rate of 10^{-4} s^{-1} at room temperature and 100°C. The dislocation density was determined by X-ray line profiles analysis. Microstructural observations performed by electron backscattering diffraction after 8 passes of equal channel angular pressing revealed very fine and homogeneous microstructure with a grain size of 0.3-6 μm. It has been found that the room temperature mechanical properties such as yield stress and tensile strength reach their maximum value even after the first pass which is in good agreement with the evolution of the dislocation density. Further processing by equal channel angular pressing led to the decrease in both the yield strength and the dislocation density, despite the slight grain size refinement.
20
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Dislocation Generation and Propagation across the Seed in Seed Cast-Si Ingots

70%
Miyamura Y., Chen J., Prakash R., Jiptner K., Harada H., Sekiguchi T.
Acta Physica Polonica A
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2014
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vol. 125
|
issue 4
1024-1026
EN
We have studied the dislocation generation and propagation from the seed crystals during seed cast Si growth. The grown ingot was cut into a vertical wafer, followed by the dislocation imaging using X-ray topography and Secco etching. The dislocation behavior at the seed area was compared with the dislocation generation at the top surface due to the thermal stress during cooling. The dislocations at the seed/crystal interface have propagated on the {111} plane toward top. When the seed surface was not melted sufficiently, the interface defect density became high, but no clear dislocation propagation was recognized. This suggests that the thermal shock at the seed/melt interface was not high enough to propagate dislocations to the growth direction. A certain amount of dislocations has been introduced from the top into the ingot according to the thermal stress. These observations suggest that optimizing the initial growth condition is important to dislocation control.
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