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1
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Photoluminescence of CdTe/CdMgTe Double Quantum Wells with a Two-Dimensional Electron Gas

100%
Deresz M., Wiater M., Karczewski G., Wojtowicz T., Łusakowski J.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
390-392
EN
Magnetophotoluminescence measurements at liquid helium temperatures were carried out on asymmetric double quantum wells based on CdTe/CdMgTe heterostructures. Due to doping with shallow iodine donors, a two-dimensional electron gas was present in the quantum wells. The samples studied differed with the quantum well widths and doping level. We show a resemblance of the luminescence to results obtained on single quantum wells which suggests that in samples studied the quantum wells are not strongly coupled.
2
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Cold and Hot Excitons in CdMnTe/CdMgTe Quantum Wells in Strong Excitation Regime and External Magnetic Field

86%
Trajnerowicz A., Golnik A., Kossacki P., Bardyszewski W., Wiater M., Karczewski G., Wojtowicz T.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
849-851
EN
Systematic studies of neutral heavy-hole excitonic line energy changes in a strong excitation regime were carried out by means of a pump-probe method for quantum wells containing a 2D gas of free holes. Energy shift of X_{e1hh1} line was analyzed for different excitation energies at fixed delay between pump and probe pulses, also under external magnetic field. It was observed that this shift depends not only on the density of created excitons but also directly on the pump energy. In co-polarization configuration for excitation energy below an absorption resonance the energetic blue shift rises linearly with the elevated exciton density (localized excitons are created). For energies slightly above the resonance, the blue shift diminishes dramatically in spite of high exciton density present (delocalized excitons are created). Model absorption calculations are in qualitative agreement with the experimental data.
3
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Excitonic Energy Shifts in CdMnTe/CdMgTe Quantum Wells under Resonant Excitation in Presence of 2D Carrier Gas

86%
Trajnerowicz A., Golnik A., Kossacki P., Bardyszewski W., Wiater M., Karczewski G., Wojtowicz T.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1403-1409
EN
Systematic studies of amplitude and energy changes of excitonic lines in a strong excitation regime were carried out by a pump-probe method. The series of samples containing quantum wells with well width from 80 Åto 140 Åwas investigated. One 80 Åsample was n-doped with iodine, the rest of the quantum wells were intentionally undoped but contained a 2D gas of free holes. Its density could be varied by changing an intensity of additional illumination. The resonant creation of high population of e1hh1 excitons causes the energetic blue shift of the same due to interactions between excitons. The blue shifts did not depend on the concentration of 2D gas of carriers whereas it did depend on the power of excitation beam. Model calculations of absorption show qualitative agreement with the experimental data.
4
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Locomotion induces changes in Trk B receptors in small diameter cells of the spinal cord

86%
Skup M., Czarkowska-Bauch J., Dwornik A., Macias M., Sulejczak D., Wiater M.
Acta Neurobiologiae Experimentalis
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2000
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vol. 60
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issue 3
371
EN
Trk B immunoreactivity (IR) was detected in number of spinal cells at the lumbar level in non-trained animals (Fig. 1A). The strongest IR appeared in the perikarya and processes of small diameter cells rarely scattered in the grey and white matter. The average area of these cells was 50 mm2 (? 10). Exercise increased by over 50% the number of TrkB immunostained small cells (Fig.1B). An enhancement of perikaryonal immunostaining of these cells was also observed (Fig.1B, inset). Testing the identity of Trk B IR small diameter cells did not prove their astroglial (GFAP IR) and gabaergic (GAD IR) phenotype in the grey matter. Some of TrkB IR cells in the white matter were astrocytes. Our data point to physical exercise as a potent method to make spinal cells more receptive to neurotrophic stimuli.
5
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Time Resolved Photoluminescence Study of the Wide (Cd,Mn)Te/(Cd,Mg)Te Quantum Well

73%
Kutrowska J., Bugajny P., Baranowski M., Bryja L., Syperek M., Wójs A., Misiewicz J., Wiater M., Karczewski G.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
895-897
EN
The static and dynamic properties of excitons and trions in a 80 nm wide Cd_{1-x}Mn_xTe/Cd_{0.7}Mg_{0.3}Te quantum well with extremely small Mn content (x=0.00027) have been studied by means of time-integrated and time-resolved photoluminescence experiment at low and elevated temperatures. The trion binding energy has been estimated to be 2.6 ± 0.8 meV. The exciton and trion lifetimes have been measured to be ≈ 150 ps, and ≈ 200 ps, respectively. The temperature dependence of both lifetimes together with the multicomponent character of the PL decay process suggest a spatial localization of excitons and trions in the investigated quantum well.
6
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Reduction of the Optical Losses in CdTe/ZnTe Thin-Film Solar Cells

73%
Chusnutdinow S., Pietruszka R., Zaleszczyk W., Makhniy V., Wiater M., Kolkovsky V., Wojtowicz T., Karczewski G.
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vol. 126
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issue 5
1072-1075
EN
We report on reduction of optical losses in n-CdTe/p-ZnTe thin-film solar cells grown by molecular beam epitaxy. The investigated thin-film devices were grown from elemental sources on monocrystalline, semi-insulating, (100)-oriented GaAs substrates. The optical losses have been reduced by a texturing of the device surface and by depositing of a ZnO antireflection coating. Current-voltage and spectral characteristics of the investigated p-ZnTe/n-CdTe solar cells depend significantly on the preparation of the surface of the ZnTe window. We describe a procedure of chemical etching of the ZnTe window leading to surface texturing. A ZnO layer of proper thickness deposited by low-temperature atomic layer deposition technique on the ZnTe surface forms an effective antireflection coating that leads to the reduction of optical losses. Due to reduction of the optical losses we observe increase of the short-circuit current, J_{SC}, by almost 60% and of the energy conversion efficiency by 44%.
7
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Deterioration of Mechanical Properties of MBE-Grown, Metastable Semiconductor Layer with Time: the Case of Zinc Blende MnTe

73%
Adamiak S., Dynowska E., Dziedzic A., Szmuc K., Janik E., Wiater M., Wojtowicz T., Szuszkiewicz W.
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EN
Several few μm thick (001)-oriented, metastable MnTe layers with the zinc blende structure grown onto (001)GaAs substrate by MBE during different periods for the last twenty years were investigated by the scanning electron microscopy, atomic force microscopy, X-ray diffraction, and nanoindentation methods. A partial decomposition of the oldest investigated layers was demonstrated. An important decrease of Young's modulus from about 34 GPa to about 17 GPa, resulting from a deterioration of the crystal structure of such layers, was found.
8
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Magnetic and Structural Study of (ZnTe)/Co Core-Shell Nanowires Grown by Molecular Beam Epitaxy

73%
Misiuna P., Dłużewski P., Wojciechowski T., Lewińska S., Ślawska-Waniewska A., Wawro A., Wiater M., Wojtowicz T., Baczewski L.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
517-519
EN
Arrays of crystalline ZnTe nanowires grown by vapor-liquid-solid mechanism were covered with cobalt in a molecular beam epitaxy system. Magnetic and structural characterization of such core/shell nanowires was performed. Using scanning electron microscopy and transmission electron microscopy it was found that the mean shell thickness of cobalt was about 35% of the nominal deposition thickness. Deposited cobalt had a polycrystalline structure covering the ZnTe nanowires evenly along their length. With the increment of temperature during Co deposition the roughness of the nanowire sidewalls increases. Vibrating sample magnetometry measurements revealed that the magnetization easy-axis direction is perpendicular to the long axis of the nanowires, which is in agreement with theoretical predictions. Oxidation of Co shell does not change the anisotropy direction of such structures, however it increases their coercivity. Exchange bias effect at the interface of cobalt and cobalt oxides suggested by some authors is not responsible for such anisotropy orientation.
9
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Terahertz Response of a Point Contact Based on CdTe/CdMgTe Quantum Well in Magnetic Field

59%
Grigelionis I., Białek M., Grynberg M., Czapkiewicz M., Kolkovskiy V., Wiater M., Wojciechowski T., Wróbel J., Wojtowicz T., But D., Knap W., Łusakowski J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1069-1072
EN
A photoresponse at THz frequencies of a quantum point contact fabricated on a CdTe/CdMgTe quantum well was studied at low temperatures as a function of magnetic field. The spectra show a structure which was interpreted as resulting from the cyclotron resonance and magnetoplasmon excitations. The wavelength of the fundamental magnetoplasmon mode was found to be about 2 μm which coincides with one of dimensions of the point contact. We also discuss the possibility of coupling of magnetoplasmon modes to shallow impurity transitions in the quantum well.
10
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Morphology and Selected Properties of Core/Shell ZnTe-Based Nanowire Structures Containing ZnO

59%
Gas K., Janik E., Zaleszczyk W., Pasternak I., Dynowska E., Fronc K., Kolkovsky V., Kret S., Morhange J., Reszka A., Wiater M., Caliebe W., Karczewski G., Kowalski B., Szuszkiewicz W., Wojtowicz T.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
612-614
EN
We report on an approach to fabricate ZnTe-based core/shell radial heterostructures containing ZnO, as well as on some of their physical properties. The molecular beam epitaxy grown ZnTe nanowires constituted the core of the investigated structures and the ZnO shells were obtained by thermal oxidation of ZnTe NWs. The influence of the parameters characterizing the oxidation process on selected properties of core/shell NWs were examined. Scanning electron microscopy revealed changes of the NWs morphology for various conditions of the oxidation process. X-ray diffraction, high resolution transmission electron microscopy, and Raman scattering measurements were applied to reveal the presence of ZnTe single crystal core and polycrystalline ZnO-shell of investigated structure.
11
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Epitaxial Growth and Optical Properties of PbTe/CdTe Semiconductor Heterostructures

59%
Szot M., Kowalczyk L., Smajek E., Domukhovski V., Domagała J., Łusakowska E., Taliashvili B., Dziawa P., Knoff W., Wiater M., Wojtowicz T., Story T.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1391-1396
EN
Growth optimization, optical and structural properties of PbTe/CdTe multilayers grown by molecular beam epitaxy on GaAs (001) as well as on BaF_2 (111) substrates is reported. An intense photoluminescence in the mid-infrared region is observed from PbTe quantum wells excited with 1.17 eV pulsed YAG:Nd laser. The energy of the emission peak shows blue shift with decreasing PbTe well width and has a positive temperature coefficient. The influence of thermal annealing on photoluminescence spectra of PbTe/CdTe multilayers grown on BaF_2 substrate is discussed.
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