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1
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The Phonon-Assisted Radiative Recombination of Excitons Confined in InAs Quantum Dashes

100%
Dusanowski Ł., Musiał A., Sęk G., Machnikowski P.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
813-816
EN
In this report we have investigated theoretically the phonon-assisted recombination process of excitons confined in strongly elongated semiconductor nanostructures, called quantum dashes. Interaction with phonon bath leads to the occurrence of phonon-assisted recombination, which in the case of acoustic phonons is manifested in the optical spectra as a deviation of the homogeneously broadened emission line shape from expected Lorentzian profile via occurrence of the so-called phonon sidebands. Hereby, we have modeled the influence of the quantum dash geometry on this spectral feature proving pronounced suppression of phonon-induced decoherence for strongly elongated nanostructures. Furthermore, the importance of different phonon coupling mechanisms has been evaluated and the spectral diffusion effects, unavoidable in the time-integrated photoluminescence experiments, have been accounted for.
2
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Calculation of Anharmonic Coupling Constants between Phonon Modes in GaAs

100%
Kolad B., Musiał A., Machnikowski P.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1167-1172
EN
We derive third-order anharmonic coupling constants between various phonon modes in a zinc-blende crystal of a binary compound using a valence force field model extended by adding Coulomb interactions between polarizable ions. We find and compare the anharmonic coupling between the zone-center LO phonon and other phonon modes along principal directions of a GaAs crystal.
3
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Development of Magnetic Properties during Annealing of Hf₂Co₁₁B Amorphous Alloy

100%
Musiał A., Śniadecki Z., Idzikowski B.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
786-788
EN
Influence of heat treatment on magnetic properties of amorphous Hf₂Co₁₁B alloy was investigated. Hard magnetic phase, characterized by high magnetic anisotropy, appears during crystallization. The highest coercive field equal to 1.86 kOe, was obtained for sample annealed in third crystallization stage. Longer heat treatment at T_{a} = 650°C leads to decrease in coercive field, which can be the result of excess of the HfCo₃B₂ phase volume fraction and additionally eutectoid transformation of hard magnetic phase into soft magnetic Co₂₃B₆ and fcc-Co. Decrease of volume fraction of hard phase is confirmed by the remanence ratio m_{r}. Value of m_{r}, for T_{a} = 650°C, is decreasing with annealing time from 0.4 to 0.27 for 30 min and 120 min, respectively. The magnetocrystalline anisotropy constant K₁ increases from 2.23 Merg/cm³ for the amorphous ribbon to 15.84 Merg/cm³ for the sample annealed at 650°C for 30 min.
4
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Crystallization Processes of R_{4.5}Fe_{77}B_{18.5} (R = Pr, Nd) Amorphous Alloys

100%
Musiał A., Śniadecki Z., Pagnani D., Idzikowski B.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
316-317
EN
The amorphous alloys R_{4.5}Fe_{77}B_{18.5} (R=Pr, Nd) were prepared by melt-spinning technique under argon atmosphere on a cooper wheel rotating with surface velocity of 25 m·s^{-1}. The ribbons have been investigated by means of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Temperatures of crystallization for Pr_{4.5}Fe_{77}B_{18.5}, measured at the heating rate 20 K/min, are equal T_{x1}=591°C for the first exothermic effect and T_{x2}=603°C for the second one (for Nd_{4.5}Fe_{77}B_{18.5} T_{x1}=594°C and T_{x2}=633°C). In the amorphous ribbons the crystallization of Fe_{3}B phase in the first step, followed by the crystallization of Pr_{2}Fe_{23}B_{3} and Nd_{2}Fe_{23}B_{3}, was observed. Both later phases appear in the process of recrystallization, immediately after Fe_{3}B formation.
5
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Electronic Structure of Elongated In_{0.3}Ga_{0.7}As/GaAs Quantum Dots

88%
Pieczarka M., Musiał A., Podemski P., Sęk G., Misiewicz J.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
809-812
EN
In this contribution the electronic structure of large In_{0.3}Ga_{0.7}As/GaAs quantum dots is studied theoretically by means of 8 band k · p modeling. These quantum dots constitute unique physical system due to the low strain limit of the Stranski-Krastanow growth mode resulting in relatively large physical volume and elongation of the quantum dots in [1-10] direction. As a result of these critical growth conditions the electronic structure is expected to be very sensitive to the nanostructure size, shape, and composition of the quantum dot as well as the accompanying wetting layer. Another peculiarity of investigated system is the confining potential which is rather shallow and weakened in comparison to standard quantum dots. It makes them very interesting in view of both fundamental study and potential applications. To reveal physical mechanisms determining the optical properties of the investigated system, the electronic structure, mainly the number of confined states, and the wave function extension as a function of both quantum dot size and geometry have been simulated numerically and the importance of electron-hole Coulomb interactions has been evaluated.
6
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Magnetic Properties and Structure of Amorphous Fe_{74}Hf_{4}Ta_{1}Cu_{1}Gd_{1}La_{x}Si_{15-x}B_{4} (x = 0, 7) Ribbons

76%
Bardziński P., Kopcewicz M., Rybaczuk M., Hasiak M., Musiał A., Kinzhybalo V., Idzikowski B.
Acta Physica Polonica A
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2015
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vol. 127
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issue 3
827-830
EN
The multi component Fe_{74}Hf_{4}Ta_{1}Cu_{1}Gd_{1}La_{x}Si_{15-x}B_{4} (x = 0, 7) alloys are promising candidates in the search for materials with unusual mechanical and magnetic properties. Amorphous nature of melt-spun samples was confirmed by X-ray diffractometry and Mössbauer spectroscopy. The X-ray diffraction patterns revealed a distinct amorphous halo. The low-field components of magnetic hyperfine field distributions on iron nuclei are observed in the Mössbauer spectra, with average hyperfine field values of 19.9 and 15.7 T for x = 0 and x = 7, respectively. Coercivity studied by vibrating sample magnetometer was about 12 A/m for x = 0 and 82 A/m for x = 7 at 300 K and about 600 A/m for x = 0 and 1200 A/m for x = 7 at 400 K. Remanence also changed with temperature, amounting to 0.64 T for x = 0 and 0.36 T for x = 7 at 300 K, while at 400 K it was 0.43 and 0.11 T for x = 0 and x = 7, respectively. It is shown that La addition has beneficial effect of shifting the Curie point towards lower temperatures together with the increase of magnitude of magnetization.
7
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Hole Subband Mixing and Polarization of Luminescence from Quantum Dashes: A Simple Model

76%
Kaczmarkiewicz P., Musiał A., Sęk G., Podemski P., Machnikowski P., Misiewicz J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
633-636
EN
In this paper, we address the problem of luminescence polarization in the case of nanostructures characterized by an in-plane shape asymmetry. We develop a simple semi-qualitative model revealing the mechanism that accounts for the selective polarization properties of such structures. It shows that they are not a straightforward consequence of the geometry but are related to it via valence subband mixing. Our model allows us to predict the degree of polarization dependence on the in-plane dimensions of investigated structures assuming a predominantly heavy hole character of the valence band states, simplifying the shape of confining potential and neglecting the influence of the out-of-plane dimension. The energy dependence modeling reveals the importance of different excited states in subsequent spectral ranges leading to non-monotonic character of the degree of polarization. The modeling results show good agreement with the experimental data for an ensemble of InAs/InP quantum dashes for a set of realistic parameters with the heavy-light hole states separation being the only adjustable one. All characteristic features are reproduced in the framework of the proposed model and their origin can be well explained and understood. We also make some further predictions about the influence of both the internal characteristics of the nanostructures (e.g. height) and the external conditions (excitation power, temperature) on the overall degree of polarization.
8
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GaAs-Based Quantum Well Exciton-Polaritons beyond 1 μm

64%
Pieczarka M., Podemski P., Musiał A., Ryczko K., Sęk G., Misiewicz J., Langer F., Höfling S., Kamp M., Forchel A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
817-820
EN
Realization of the Bose-Einstein condensate can provide a way for creation of an inversion-free coherent light emitter with ultra-low threshold power. The currently considered solutions provide polaritonic emitters in a spectral range far below 1 μm limiting their application potential. Hereby, we present optical studies of InGaAs/GaAs based quantum well in a cavity structure exhibiting polaritonic eigenmodes from 5 to 160 K at a record wavelength exceeding 1 μm. The obtained Rabi splitting of 7 meV was almost constant with temperature, and the resulting coupling constant is close to the calculated QW exciton binding energy. This indicates the very strong coupling conditions explaining the observation of polaritons at temperatures where the exciton dissociation is already expected, and allows predicting that room temperature polaritons could still be formed in this kind of a system.
9
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Effect of Confinement Anisotropy on Excitonic Properties in InAs/InP Quantum Dashes

64%
Mrowiński P., Musiał A., Sęk G., Misiewicz J., Höfling S., Somers A., Hein S., Forchel A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
801-804
EN
The influence of confinement potential anisotropy on emission properties of strongly elongated single InAs/InGaAlAs/InP quantum dashes has been investigated by polarization-resolved microphotoluminescence spectroscopy at around 1.5 μm. There have been determined the exciton fine structure splitting, degree of linear polarization of surface emission and biexciton binding energy. The investigated dashes exhibited usually: the exciton anisotropy splitting larger than 100 μeV, the corresponding biexciton binding energy of about 3 meV, and the degree of linear polarization values in the range from 24% to 55%. Here, we presented a correlation of these parameters for several quantum dashes, which can be attributed either to a change in lateral aspect ratio within the ensemble, or the carrier localization on random fluctuations of the dash confinement potential.
10
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Temperature Dependence of Photoluminescence from Epitaxial InGaAs/GaAs Quantum Dots with High Lateral Aspect Ratio

64%
Musiał A., Sęk G., Maryński A., Podemski P., Misiewicz J., Löffler A., Höfling S., Reitzenstein S., Reithmaier J., Forchel A.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
883-887
EN
Hereby, we present a study of a thermal quenching of emission from self-assembled epitaxial highly asymmetric quantum dots in InGaAs/GaAs material system for both ensemble and single dot regime. Pronounced interplay between the intensity of wetting layer and quantum dots originated emission was observed as the temperature was increased, evidencing a thermally activated energy transfer between the two parts of the system and an important role of the wetting layer in determining the optical properties of these anisotropic nanostructures. The carrier activation energies have been derived and possible carrier loss mechanisms have been analyzed. Single dot study revealed activation energies slightly varying from dot to dot due to size and shape distribution. The problem of the shape uniformity of individual quantum dot has also been addressed and possibility of additional carrier localization within the investigated structures has been found to be insignificant based on the recorded spectroscopic data.
11
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Optimizing the InGaAs/GaAs Quantum Dots for 1.3 μm Emission

52%
Maryński A., Mrowiński P., Ryczko K., Podemski P., Gawarecki K., Musiał A., Misiewicz J., Quandt D., Strittmatter A., Rodt S., Reitzenstein S., Sęk G.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
386-390
EN
Hereby we present comprehensive experimental and theoretical study on fundamental optical properties and electronic structure of GaAs-based quantum dots grown using metalorganic chemical vapor deposition technique. The substantial redshift of emission, to the second telecommunication window of 1.3 μm, in comparison to standard InGaAs/GaAs quantum dots is obtained via strain engineering utilizing additional capping layer of In_{0.2}Ga_{0.8}As in this context referred to as strain reducing layer. It ensures lowering of the energy of the ground state transition to more application relevant spectral range. Optical properties of the quantum dot structure has been experimentally characterized by means of photoreflectance spectroscopy and power-dependent photoluminescence revealing 3 transitions originating from hybrid states confined in an asymmetric double quantum well formed of the wetting layer and strain reducing layer, as well as higher states of the quantum dots themselves with the first excited state transition separated by 67 meV from the ground state transition. Origin of the observed transitions was confirmed in theoretical modelling using 1-band single-particle approach for the quantum well part, and excitonic quantum dot spectrum obtained within 8 band k·p formalism followed by configuration interaction calculations, respectively. Additionally, photoluminescence excitation spectroscopy measurements allowed to identify a spectral range for efficient quasi-resonant excitation of the investigated quantum dots into the 2D density of states to be in the range of 835-905 nm.
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