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1
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Efficient Emission from InAlGaAs Single Quantum Dots with Low Lattice Misfit and AlGaAs Indirect Bandgap Barrier

100%
Słupiński T., Korona K., Papierska J., Borysiuk J.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1229-1232
EN
We report on molecular beam epitaxy growth and properties of rarely studied quaternary In_{0.4}(Al_{0.75}Ga_{0.25})_{0.6}As self-assembled quantum dots, which show strong and efficient emission of red light from single quantum dots. The increased yield is, among others, due to efficient energy transfer from indirect band-gap Al_{0.75}Ga_{0.25}As barriers. To maximize photon energy emitted from quantum dots, low In composition, x_{In} = 0.4 was applied, which also lowered the lattice misfit close to the limit of 2D/3D transition in the Stranski-Krastanov growth mode. Time-resolved micro-photoluminescence shows emission at 650-750 nm. Well-resolved single quantum dot photoluminescence lines (decay time of ≈ 1-2 ns) are observed despite a high concentration ≈ 3×10¹¹ cm¯² of quantum dots. We discuss this observation assuming newly a role of carriers or excitons diffusion/tunneling between quantum dots at high surface concentration of dots and a possible role of lattice disorder inside the dot on the exciton lifetime.
2
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Influence of Electric Field on Recombination Dynamics of Quantum Confined Carriers

100%
Korona K., Borysiuk J., Skierbiszewski C., Porowski S.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
243-247
EN
We present time-resolved photoluminescence measurements of GaN/AlGaN low dimensional structures showing very characteristic changes of dynamics related to strong electric field. Strong piezoelectric and spontaneous polarizations built-in in nitride structures lead to the changes in spatial separation of carriers which leads to changes in recombination energies and radiative lifetimes of the carriers. The observed effect can be well described by a simple exponential relation. The observed dependence can be explained by an approximated model of quantum-confined Stark effect based on the Airy functions.
3
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On Correlations between Extended Defects Formation and Electron Concentration Changes Caused by Annealing of GaAs:Te

100%
Borysiuk J., Kozubowski J., Słupiński T.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
739-742
EN
Extended type defects in heavily doped GaAs:Te (n≈1×10^{19} cm^{-3}) after annealing at 700°C and 1150°C were studied by transmission electron microscopy, by high resolution technique and energy-dispersive X-ray analysis. Assuming, according to the literature that these defects are enriched in impurity atoms it is suggested that this solely is not sufficient to explain changes of electrical properties during annealing. Estimated amount of atoms involved in faulted dislocation loops seems to be too small, energy-dispersive X-ray microanalysis of precipitates did not show large differences in composition with the matrix.
4
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Transmission Electron Microscopy and Luminescence Studies of Quantum Well Structures Resulting from Stacking Fault Formation in 4H-SiC Layers

88%
Borysiuk J., Wysmołek A., Bożek R., Strupiński W., Baranowski J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1067-1072
EN
Transmission electron microscopy and photoluminescence studies of quantum well structures related to stacking faults formation in 4H-SiC homoepitaxial layers are reported. The investigated 4H-SiC layers were deposited on 8° misoriented Si-terminated (0001) surface of high quality 4H-SiC substrate. It is found that the planar defects created by direct continuation from the SiC substrates are cubic 3C-SiC stacking faults. These defects are optically active, giving rise to characteristic luminescence band in the spectral range around 2.9 eV, which consist of several emission lines. The observed energy and intensity pattern of this emission is discussed of in terms of single, double and multiple quantum wells formed from neighboring 3C-SiC SF layers embedded in 4H-SiC material.
5
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Quantum Confinement in InAs/GaAs Systems with Self-Assembled Quantum Dots Grown Using In-Flush Technique

88%
Molas M., Kuldová K., Borysiuk J., Wasilewski Z., Babiński A.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
624-626
EN
The effect of In-flush technique application to the MBE-grown structure with self-assembled quantum dots is investigated in this work. The microphotoluminescence from structures with the InAs/GaAs dots grown with and without the In-flush has been investigated. We focus our attention on "not fully developed" dots, which can be clearly distinguished in the spectrum. The dots have also been identified in the transmission electron microscopy analysis of the structures. The In-flush does not influence a broad energy range of those features. Instead we have found that the anisotropic exchange energy splitting of neutral excitons confined in those in the structure grown with In-flush is substantially lower that the splitting in the structure with no In-flush. This observation confirms that the In-flush leads not only to better uniformity of self-assembled quantum dots but also to reduction of lateral potential, anisotropy, which is believed to result in the neutral exciton splitting.
6
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MnAs Nanocrystals Embedded in GaAs

76%
Kwiatkowski A., Wasik D., Kamińska M., Twardowski A., Dłużewski P., Borysiuk J., Sadowski J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1207-1211
EN
Magnetic properties of MnAs nanocrystals embedded in GaAs are analyzed in the frame of phenomenological model proposed by Sasaki for ferritin superparamagnets. Our calculations explain qualitatively experimental data of magnetization versus temperature, obtained according to zero-field-cooled and field-cooled protocols. They show dynamics of magnetization of MnAs nanocrystals in range of temperature from 10 K to 320 K. There is transition from state in which very slow dynamics is observed (frozen state) to state in which dynamics is fast (quasi-superparamagnetic state).
7
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Absorption and Emission Properties of Light Emitting Diode Structures Containing GaInN/GaN QWs

76%
Binder J., Korona K., Borysiuk J., Wysmołek A., Baeumler M., Köhler K., Kirste L.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
918-920
EN
In this work we present measurements of GaInN/GaN light emitting diodes (LEDs) with an active layer consisting of three quantum wells made of Ga_{0.9}In_{0.10}N that have different widths (1.8 nm, 2.7 nm, 3.7 nm). A comparison of emission and absorption (photocurrent) on the same sample revealed a shift in energy, with the emission energy being significantly lower. The shifts are about 0.02 eV, 0.03 eV, and 0.04 eV for the quantum wells having the widths of 1.8 nm, 2.7 nm, and 3.7 nm, respectively. This can be explained by a shift of the ground state energy caused by the quantum confined Stark effect. Calculations show that due to the spontaneous polarization and the piezoelectric effect a strong electric field of the order of 1 MV/cm was present in the GaInN quantum wells. Simulations of ground-state energies in the model of an infinite square well under the influence of an electric field with a matched effective well width were performed and used to interpret the experimental results.
8
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Content available

76%
Kwiatkowski A., Borysiuk J., Bożek R., Wasik D., Kamińska M., Sadowski J., Twardowski A.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
233-236
EN
We report on cross-sectional transmission electron microscopy and magnetic force microscopy studies performed on self-organized MnAs nanoclusters embedded in GaAs. It was found that 10÷20 nm large MnAs ferromagnetic nanocrystals were formed during rapid thermal annealing of Ga_{1-x}Mn_xAs layers at 600ºC, leading to magnetic contrasts in magnetic force microscopy images.
9
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Photoluminescence Dynamics of GaN/Si Nanowires

76%
Korona K., Zytkiewicz Z., Perkowska P., Borysiuk J., Binder J., Sobanska M., Klosek K.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1001-1003
EN
In this work we present analysis of carriers dynamics in samples of GaN nanowires grown on silicon. The samples exhibit bright luminescence of bulk donor-bound excitons at 3.472 eV, surface defect-bound excitons at 3.450 eV (SDX) and a broad (0.05 eV) band centered at 3.47 eV caused probably by single free exciton and bi-exciton recombination. The SDX emission has long lifetime τ = 0.6 ns at 4 K and can be observed up to 50 K. At higher temperatures luminescence is dominated by free excitons. The broad excitonic band is best visible under high excitation, and reveals fast, non-exponential dynamics. We present mathematical model assuming exciton-exciton interaction leading to the Auger processes. The model includes n^2 (Langevin) term and describes well the non-exponential dynamics of the excitonic band.
10
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Raman Studies of Defects in Graphene Grown on SiC

76%
Grodecki K., Bożek R., Borysiuk J., Strupinski W., Wysmolek A., Stępniewski R., Baranowski J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
595-596
EN
The Raman scattering studies of multi-layer graphene obtained by high temperature annealing of carbon terminated face of 4H-SiC(000-1) substrates are presented. Intensity ratio of the D and G bands was used to estimate the average size of the graphene flakes constituting carbon structures. The obtained estimates were compared with flake sizes from atomic force microscopy data. We found that even the smallest structures observed by atomic force microscopy images are much bigger than the estimates obtained from the Raman scattering data. The obtained results are discussed in terms of different average flake sizes inside and on the surface of the multi-layer graphene structure, as well as different type of defects which would be present in the investigated structures apart from edge defects.
11
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InGaN QW in External Electric Field Controlled by Pumping of 2D-Electron Gas

76%
Korona K., Drabińska A., Surowiecka K., Wołowiec L., Borysiuk J., Caban P., Strupiński W.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1179-1186
EN
We present investigations of GaInN/GaN/AlGaN structure containing cavity designed so that the electric field inside it can be changed by illumination. Numerical calculations show that illumination can change carrier distributions and consequently change the field and potential. The electric field influences properties of a quantum well placed in the cavity. We confirmed experimentally that the electric field controlled by external bias or by optical pumping, can change energy and occupation of electronic states in the quantum well. The quantum well energy could be changed of about 80 meV by voltage and 15 meV by illumination.
12
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Neutral and Charged Excitons Localized in the InAs/GaAs Wetting Layer

64%
Babiński A., Czyż M., Golnik A., Borysiuk J., Kret S., Raymond S., Lapointe J., Wasilewski Z.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1055-1060
EN
It has recently been shown that potential fluctuations in a wetting layer, which accompanies InAs/GaAs quantum dots can localize excitons. Neutral excitons and biexcitons and charged excitons were identified. In this communication we report on studies of properties of the excitons over wide temperature range (T < 70 K). The micro-photoluminescence measurements enable investigation of excitons localized in a single potential fluctuation. Temperature-induced broadening of the neutral exciton as well as a quenching of the charged exciton at temperatures higher than 50 K are observed and discussed.
13
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Carbon-Encapsulated Magnetic Nanoparticles Based on Fe, Mn, and Cr for Spintronics Applications

64%
Szczytko J., Osewski P., Bystrzejewski M., Borysiuk J., Grabias A., Huczko A., Lange H., Majhofer A., Twardowski A.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
305-310
EN
We succeeded in the arc-plasma synthesis of carbon-encapsulated Fe, Cr, and Mn-based nanoparticles. The transmission electron microscopy, Mössbauer spectra (of iron) and SQUID magnetometry results demonstrate that the products of the synthesis contain metals and its carbides. The nanoparticles show ferromagnetic or superparamagnetic behavior at high temperatures, which is demanded for nano-spintronics applications.
14
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Properties of GaN Nanocolumns Grown by Plasma - Assisted MBE on Si (111) Substrates

64%
Zytkiewicz Z., Dluzewski P., Borysiuk J., Sobanska M., Klosek K., Witkowski B., Setkiewicz M., Pustelny T.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6A
A-15-A-16
EN
We report on growth of GaN nanocolumns by plasma assisted MBE on (111) silicon substrates and on their characterization. The nanocolumns nucleate on the substrate spontaneously without use of any catalyst, probably by the Volmer-Weber mechanism. Transmission electron microscopy analysis shows high crystalline quality of GaN nanocolumns and their good alignment with the c-axis being perpendicular to the substrate. Preliminary results on use of GaN nanocolumns in gas sensor devices are presented.
15
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Optical Absorption and Raman Scattering Studies of Few-Layer Epitaxial Graphene Grown on 4H-SiC Substrates

64%
Grodecki K., Drabińska A., Bożek R., Wysmołek A., Korona K., Strupiński W., Borysiuk J., Stępniewski R., Baranowski J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
835-837
EN
Optical absorption and Raman scattering studies of few-layer epitaxial graphene obtained by high temperature annealing of carbon terminated face of 4H-SiC(000-1) on-axis substrates are presented. Changing the pressure and annealing time, different stages of the graphene formation were achieved. Optical absorption measurements enabled us to establish average number of graphene layers covering the SiC substrate. Raman scattering experiments showed that integrated intensity of the characteristic 2D peak positively correlated with the number of graphene layers deposited on the SiC substrate. The spectral width of the 2D peak was found to decrease with the number of the deposited graphene layers.
16
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Content available

Fabrication and Physical Properties of SiC-GaAs Nano-Composites

64%
Kalisz G., Grzanka E., Wasik D., Świderska-Środa A., Gierlotka S., Borysiuk J., Kamińska M., Twardowski A., Pałosz B.
Acta Physica Polonica A
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2005
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vol. 108
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issue 4
717-721
EN
Nano-composites consisting of primary phase of hard nanocrystalline SiC matrix and the secondary nanocrystalline semiconductor (GaAs) phase were obtained by high-pressure zone infiltration. The synthesis process occurs in three stages: (i) at room temperature the nanopowder of SiC is compacted along with GaAs under high pressure up to 8 GPa, (ii) the temperature is increased above the melting point of GaAs up to 1600~K and, the pores are being filled with liquid, (iii) upon cooling GaAs nanocrystallites grow in the pores. Synthesis of nano-composites was performed using a toroid-type high-pressure apparatus (IHPP of the Polish Academy of Sciences, Warsaw) and six-anvil cubic press (MAX-80 at HASYLAB, Hamburg). X-ray diffraction studies were performed using a laboratory D5000 Siemens diffractometer. Phase composition, grain size, and macrostrains present in the synthesized materials were examined. Microstructure of the composites was characterized using scanning electron microscopy and high resolution transmission electron microscopy. Far-infrared reflectivity measurements were used to determine built-in strain.
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