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1
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Valence Band Quantization in a Spherical Quantum Dot

100%
Buczko R.
Acta Physica Polonica A
|
1992
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vol. 82
|
issue 5
789-792
EN
An analytical solution of the effective mass equation for a spherical valence band in cubic semiconductors is presented. The full degeneracy of the valence band, i.e. the light-hole, heavy-hole and spin-orbit split-off subbands, were taken into account. The analytical wave functions of the valence band were used for its quantization in a completely isolated (infinite potential barrier approximation) quantum dot. The dependence of discrete valence levels on the dot diameter is presented for the CuCl case.
2
Content available remote

Impurity Wave Function and Alloy Broadening of Impurity-Related Luminescence

64%
Buczko R., Langer J.
Acta Physica Polonica A
|
1993
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vol. 84
|
issue 3
591-594
EN
By performing state-of-art computations of the acceptor wave functions in GaAs we show that the linewidth of the conduction band to acceptor luminescence increases more than quadratically with the increase in the binding energy. This proves that study of the fluctuation broadening of the impurity-related emission in semiconductor alloys may provide a critical test for theories claiming realistic impurity wave function computation. The theoretical results are compared with the experimental data for high purity p-type AlGaAs alloys.
3
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Bound and Resonant States of Shallow Donors in Quantum Antidots

64%
Buczko R., Bassani F.
Acta Physica Polonica A
|
1996
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vol. 90
|
issue 4
743-746
EN
The energy spectrum and the wave functions of a shallow donor placed at the center of a spherical quantum antidot are computed within the effective mass approximation. The wave functions for discrete bound states and for continuum states are obtained in a closed form. We show that, due to the local potential of the microstructure, resonances occur in the continuum. Their energies are close to those of hydrogen-like levels lying under the top of the barrier when the quantum antidot radius is large as compared to the effective Bohr radius. The lifetimes of the resonant states and the oscillator strengths for optical transitions from the ground state are computed. We show how the energy spectrum and the oscillator strengths depend on the antidot parameters.
4
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Ultra-Fast Spin Dynamics in Diluted Magnetic Semiconductors

51%
Wilamowski Z., Buczko R., Karczewski G., Jantsch W.
Acta Physica Polonica A
|
1996
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vol. 90
|
issue 5
969-972
EN
In nano-size antiferromagnetic systems a spatially inhomogeneous field leads to the formation of a staggered magnetization. Thereby the total magnetic moment does not change but the formation of a net magnetic moment at the border of the cluster leads to an energy gain. This type of magnetism is characterised by an ultra-fast dynamics. We suggest it is also responsible for the formation of the exciton magnetic polaron.
5
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Magnesium Acceptor Energy Levels in Cubic GaN

51%
Przybylińska H., Buczko R., Kocher G., Jantsch W.
Acta Physica Polonica A
|
2003
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vol. 103
|
issue 6
683-688
EN
Intra-impurity transitions of the Mg acceptor in cubic phase GaN were measured with the use of photothermal ionization spectroscopy. Apart from the photoionization band several sharp features were detected, related to internal Mg-acceptor transitions. The transitions were identified with the help of effective-mass model calculations involving light- and heavy-hole as well as spin--orbit split-off bands. Transitions to resonant states, associated with the spin-orbit split-off valence band, were also identified. The determined hole binding energy of the Mg acceptor in zinc-blende GaN is 236±1 meV.
6
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Quantum Phenomena in Small Antiferromagnets

51%
Wilamowski Z., Buczko R., Jantsch W.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 2
379-382
EN
We show that the most characteristic properties of mesoscopic antiferromagnets can be explained in terms of the response on a spatially inhomogeneous perturbation. This concept allows to explain the dynamic properties (quantum resonance, coherence and tunnelling rates) as well as static perturbations which, for increasing size of an antiferromagnet, leads to a transition from the quantum mechanical oscillating system to a classical antiferromagnet with well defined Néel vectors.
7
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Resonant Photoemission Study οf 4f Electrons on the Surface οf Semiconductors

51%
Orłowski B., Kowalski B., Pietrzyk M., Buczko R.
Acta Physica Polonica A
|
2008
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vol. 114
|
issue S
S-103-S-114
EN
The contribution of 4f electrons to the electronic structure of the semiconductor clean surface caused by the surface doping of it by rare-earth metal atoms (Eu, Sm) will be presented. The surface doping was performed by the controlled, sequential deposition of the rare-earth metal atoms on the clean surface in UHV conditions (Sm on GaN or CdTe) or by the doping of the layer volume of (EuGd)Te. After each deposition or surface treatment the synchrotron radiation was used to measure in situ the resonant photoemission spectra (the Fano type resonance) to study the contribution of 4f electrons of divalent and trivalent Sm and Eu ions to the valence band electronic structure of created sample. The first stages of the metal atoms deposition lead to the surface doping. Further metal atoms deposition leads to the growth of the metallic islands on the surface and causes the appearance of the sharp metallic Fermi edge in the energy distribution curves. Proper coverage and annealing of the sample surface with metal atoms leads to the diffusion of the metal atoms into the sample and results in an increase in the crystal doping and decrease in the metallic islands contribution to the measured spectra. As a result, the new electronic structure of the valence band can be created and investigated in situ.
8
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"Comb-Like" Polarons and Bipolarons in High-T_{c} Materials

51%
Hankiewicz E., Buczko R., Wilamowski Z.
Acta Physica Polonica A
|
2000
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vol. 97
|
issue 1
185-188
EN
Diagonalization of Hamiltonian composed from d-d exchange interactions between localized d spins of antiferromagnetic cluster and p-d interaction with the spin of carriers indicates a possibility of formation of pure magnetic polarons. The most energetically favorable solution occurs when the carrier density in CuO_{2} planes is distributed on every second spin. These "comb-like" polarons have a tendency to bind into pairs (bipolarons) "glued" by the antiferromagnetic medium.
9
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Small Antiferromagnetic Clusters

51%
Buczko R., Wilamowski Z., Jantsch W.
Acta Physica Polonica A
|
1996
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vol. 90
|
issue 4
747-750
EN
The analysis of the quantum mechanical model of mesoscopic size antiferromagnets shows that small antiferromagnets are characterized by a stronger exchange coupling and by an oscillating character of spins polarizations. Experimental evidence of the quantum character is discussed. We interpret the interlayer coupling in antiferromagnet superlattices and a puzzling resonance observed in nano-size antiferromagnet grains.
10
Content available remote

Quantum Spin Hall Effect in Strained (111)-Oriented SnSe Layers

51%
Safaei S., Galicka M., Kacman P., Buczko R.
Acta Physica Polonica A
|
2016
|
vol. 129
|
issue 1a
A-150-A-152
EN
Recently, the quantum spin Hall effect has been predicted in (111)-oriented thin films of SnSe and SnTe topological crystalline insulators. It was shown that in these films the energy gaps in the two-dimensional band spectrum depend in an oscillat ory fashion on the layer thickness - the calculated topological invariant indexes and edge state spin polarizations show that for films 20-40 monolayers thick a two-dimensional topological insulator phase appears. Edge states with the Dirac cones with opposite spin polarization in their two branches are obtained for both materials. However, for all but the (111)-oriented SnTe films with an even number of monolayers an overlapping of bands in Γ̅ and M̅ diminishes the final band gap and the edge states appear either against the background of the bands or within a very small energy gap. Here we show that this problem in SnSe films can be removed by applying an appropriate strain. This should enable observation of the quantum spin Hall effect also in SnSe layers.
11
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Modeling of Small Diameter Semiconductor Nanowires

51%
Bukała M., Galicka M., Buczko R., Kacman P.
Acta Physica Polonica A
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2007
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vol. 112
|
issue 2
425-430
EN
The properties of very thin (up to 16Å diameter) wires, cut out from the bulk in either zinc-blende or wurtzite material, are studied theoretically. In the total energy calculations we use ab initio methods and consider three different crystallographic growth axes for the zinc-blende and one for the wurtzite structure. We show that the most stable zinc-blende nanowires are those growing along (111) direction, however, the wurtzite structure is found to be energetically more favorable than the zinc-blende for wires of the same diameter. In addition, the band structure of the wires was calculated.
12
Content available remote

Magnetic Properties of Semiconductor-Antiferromagnet Superlattices

45%
Wilamowski Z., Buczko R., Jantsch W., Ludwig M., Springholz G.
Acta Physica Polonica A
|
1996
|
vol. 90
|
issue 5
973-976
EN
Magnetic resonance investigations of ultra-thin antiferromagnetic EuTe layers show a specific behaviour in the quasi-2D antiferromagnetic ordering: (i) an anisotropy of the critical broadening, (ii) a substantial increase in the Néel temperature and (iii) an anisotropic shift of the resonance frequency which diverges at the Néel point. The results show that exchange coupling is stronger in quasi-2D than in 3D antiferromagnetic samples and that correlation of spin chains aligned in the perpendicular direction occurs already well above the Néel point.
13
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Optical Γ₆ → Γ₈ Free-to-Bound Transitions in Acceptor δ-Doped Single Heterostructure - Theoretical Analysis

45%
Buczko R., Łusakowski J., Friedland K., Hey R., Ploog K.
Acta Physica Polonica A
|
2008
|
vol. 114
|
issue 5
1079-1083
EN
A theoretical analysis was carried out of an optical transition observed in high-quality GaAs/AlGaAs heterostructures δ-doped with shallow acceptors. The transition involves a 2D electron and a 3D acceptor-localized hole. The wave functions of a bulk Be acceptor were calculated within the spherical model with both the s-like and d-like parts of the envelope taken into account. The electron envelope wave functions resulted from self-consistent calculations of the electrostatic potential and were dependent on the 2D electron concentration, n_s. We show that: (i) including the d-like part of the acceptor envelope relaxes the selection rules of free-to-bound transitions at k=0;(ii) in the magnetic field, the selection rules depend on the number of the electron Landau level;(iii) the ratio of the intensity of the strongest transitions in both circular polarizations is essentially different from 3:1, and strongly depends on n_s. These results show that a description that neglects the d-like part of the acceptor envelope is both qualitatively and quantitatively unjustified.
14
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Spectroscopy of Be Acceptor Ground State in GaAs/AlGaAs Heterostructure

39%
Łusakowski J., Buczko R., Sakowicz M., Friedland K., Hey R., Ploog K.
Acta Physica Polonica A
|
2007
|
vol. 112
|
issue 2
209-213
EN
Photoluminescence measurements were carried out on Be δ-doped GaAs/Al_{0.33}Ga_{0.67}As heterostructure at 1.6 K in magnetic fields (B) up to 4 T. Luminescence originating from recombination of a two-dimensional electron gas and photoexcited holes localized on Be acceptors was analyzed. The degree of circular polarization (γ_C) of the luminescence from fully occupied Landau levels was determined as a function of B and the two-dimensional electron gas concentration, n_s. At B constant,γ_C decreased with the increase in n_s. The intensity of the optical transition considered was calculated with taking into account s- and d-like parts of the acceptor envelope function. It is shown that the presence of the d-like part explains the observed γ_C(n_s) dependence quantitatively. This shows that polarization spectroscopy on acceptorδ-doped heterostructures enables one to test experimentally the contribution of the L>0 component of the envelope in a shallow acceptor description.
15
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Experimental and Theoretical Analysis οf PbTe-CdTe Solid Solution Grown by Physical Vapour Transport Method

27%
Szot M., Szczerbakow A., Dybko K., Kowalczyk L., Smajek E., Domukhovski V., Łusakowska E., Dziawa P., Mycielski A., Story T., Bukała M., Galicka M., Sankowski P., Buczko R., Kacman P.
Acta Physica Polonica A
|
2009
|
vol. 116
|
issue 5
959-961
EN
Bulk monocrystals of Pb_{1-x}Cd_{x}Te, with the Cd content x up to 0.11, were grown by physical vapour transport method. The structural, electrical and optical properties of these ternary crystals were studied experimentally and theoretically. All investigated samples exhibit rock-salt structure and high crystal quality, which was confirmed by X-ray rocking curve width parameter of about 100 arcsec. The decrease of the lattice parameter with increasing Cd content x was found experimentally, in agreement with ab initio calculations. The band structures of Pb_{1-x}Cd_{x}Te mixed crystals for x values up to 0.2 were calculated using tight binding approach. The calculated band gap in the L-point increases with the Cd content in qualitative agreement with photoluminescence measurements in the infrared. For all studied Pb_{1-x}Cd_{x}Te samples, the Hall effect and electrical conductivity measurements, performed in the temperature range from 4 to 300 K, revealed p-type conductivity.
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