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1
Content available remote

Scattering of Excitons by Phonons in Quantum Wells

100%
Bardyszewski W., Prywata M.
Acta Physica Polonica A
|
1996
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vol. 90
|
issue 4
715-718
EN
A method to describe the effects of the exciton-optical phonon interaction is presented using the cumulant expansion approximation. The functional-integral technique of coherent phonon states is used in order to justify the commonly used model Hamiltonian and generate the proper perturbation series. The influence of the mutual electron-hole screening on the polaronic effects in quantum wells is analyzed.
2
Content available remote

Exciton Absorption in GaN

100%
Sobol M., Bardyszewski W.
Acta Physica Polonica A
|
1998
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vol. 94
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issue 3
534-538
EN
The absorption coefficient of the wurtzite-type GaN is described in terms of three almost totally decoupled excitons A, B, C associated with split valence bands of Γ_{9}, Γ_{7} and Γ_{7} symmetries using a spherically symmetric approximation for the standard effective-mass Hamiltonian. The excitonic equations are solved within the subspace of optically active states of s-symmetry. The effects of crystal field and spin-orbit coupling are discussed. The results show that the spherical approximation is in perfect agreement with experimental findings.
3
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Symmetry of the Top Valence Band States in GaN/AlGaN Quantum Wells and its Influence on the Polarization of Emitted Light

100%
Bardyszewski W., Łepkowski S.
Acta Physica Polonica A
|
2011
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vol. 120
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issue 5
894-896
EN
We show theoretically that for narrow GaN/AlGaN quantum wells, lattice matched to GaN substrate/buffer and grown along the (0001) crystallographic direction the topmost valence subband symmetry depends critically on such parameters as quantum well thickness and barrier composition. This effect determines polarization of the emitted light. It is noted that the symmetry of the topmost valence band level is sensitive to the values of the D_3 and D_4 deformation potentials and can be employed in verification of existing literature values of these parameters.
4
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Pressure-Driven Reordering of Valence Band States in AlGaN/AlN Quantum Wells

100%
Łepkowski S., Bardyszewski W.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1029-1030
EN
We study theoretically the influence of external hydrostatic pressure on the valence band structure in [0001]-oriented Al_{x}Ga_{1-x}N/AlN quantum wells used in deep-ultraviolet light emitting devices. The calculations performed using the multi-band k·p method with excitonic effects show that for Al_{x}Ga_{1-x}N/AlN quantum wells with x = 0.7 and quantum well width of 1.5 nm, reordering of the topmost valence subbands having different symmetries occurs with increasing pressure. In these structures, at low pressure values the topmost valence level is of Γp_9 symmetry whereas it changes to the Γp_7 state for pressures about 2.5 GPa. We also find that the excitonic effects increase the critical value of pressure at which the change in the polarization of the emitted light occurs to 7 GPa. This behavior is opposite to the pressure-dependent reordering of the topmost valence band states in thin GaN/AlGaN quantum wells which occurs from Γp_7 to Γp_9 states.
5
Content available remote

Polaron Problem in Quantum Wells

100%
Bardyszewski W., Prywata M.
Acta Physica Polonica A
|
1995
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vol. 88
|
issue 5
969-973
EN
The effect of polar interaction between an electron in a quantum well and bulk longitudinal optical phonons is analysed. Electron spectral density function is calculated in the lowest order cumulant approximation. The position and linewidth of the quasiparticle peak are obtained as a function of quantum well width and temperature.
6
Content available remote

Plasma Edge Modification in Strongly Compensated Semiconductors

81%
Szuszkiewicz W., Dybko K., Bardyszewski W., Julien C.
Acta Physica Polonica A
|
1995
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vol. 88
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issue 5
1048-1052
EN
We demonstrate that the electron-impurity interaction can modify the reflectivity in the vicinity of plasma minimum giving rise to a small dip on the plasma edge. Experimental spectra taken for Hg_{1-x}Co_{x}Se for x < 0.02 at various temperatures confirm this theoretical prediction. The position of the structure can be used to determine the plasma frequency in highly compensated materials at low temperatures.
7
Content available remote

Influence of Plasmon-Phonon Coupling on the Electron-Impurity Interaction in the Free-Carrier Absorption

81%
Szuszkiewicz W., Bardyszewski W., Julien C.
Acta Physica Polonica A
|
1995
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vol. 87
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issue 2
555-558
EN
An experimental and theoretical evidence that the electron-impurity scattering is modified in the presence of the electromagnetic field oscillating with the frequency corresponding to the optical phonon energy is given. The coupled plasmon-phonon mode related feature in the reflectivity spectrum can be used to determine the upper edge of the LO phonon frequency band in highly doped materials.
8
Content available remote

Band Mixing Effects in Quantum Well Magnetoexcitons

81%
Wysocki R., Bardyszewski W., Schoser S., Potemski M.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
1067-1071
EN
The influence of intersubband mixing in quantum wells of semiconductors with zinc-blende structure is studied both experimentally and theoretically. A multiband magnetoexciton model is described which takes into account k∙p mixing between valence subbands and the effective Coulomb interaction for an arbitrary confinement potential shape. Theoretical results reproduce very well the photoluminescence excitation spectra of GaAs/AlGaAs single quantum wells of various widths. In particular, the characteristic avoided crossing between the lowest light-hole exciton Landau level and excited heavy-hole exciton Landau level occurring at σ¯ polarization is accurately described by our theory.
9
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Effect of the Built-In Strain on the In-Plane Optical Anisotropy of m-Plane GaN/AlGaN Quantum Wells

81%
Łepkowski S., Bardyszewski W., Teisseyre H.
Acta Physica Polonica A
|
2011
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vol. 120
|
issue 5
897-898
EN
We study theoretically the influence of the anisotropic biaxial strain originating from the lattice mismatch between the m-plane GaN/AlGaN quantum wells structure and the substrate on the optical anisotropy of such systems. It is demonstrated that the oscillator strengths for optical transitions with polarization of light parallel and perpendicular to the crystal axis c strongly depend on strain to such an extent that, by increasing the concentration of Al in the substrate from x = 0 to x = 0.5 one can change the polarization of the emitted light with respect to the c-axis by 90 degrees.
10
Content available remote

Pressure Dependence of Exciton Binding Energy in GaN/Al_{x}Ga_{1 - x}N Quantum Wells

81%
Bardyszewski W., Łepkowski S., Teisseyre H.
Acta Physica Polonica A
|
2011
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vol. 119
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issue 5
663-665
EN
We present a theoretical study of excitons in GaN/Al_{x}Ga_{1 - x}N wurtzite (0001) quantum wells subjected to hydrostatic pressure. Our results show that the combined effect of pressure induced changes in band structure and piezoelectric field leads to reduction of the exciton binding energy. This subtle effect is described quite accurately by our multiband model of excitons in quantum wells.
11
Content available remote

Polarization-Induced Band Inversion in In-Rich InGaN/GaN Quantum Wells

81%
Łepkowski S., Bardyszewski W., Rodak D.
Acta Physica Polonica A
|
2014
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vol. 126
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issue 5
1154-1155
EN
We theoretically study the polarization-induced band inversion phenomenon in c-plane In-rich InGaN/GaN quantum wells. Our calculations performed using the k·p method with the 8×8 Rashba-Sheka-Pikus Hamiltonian for the structures with the indium content between 90% and 100% show that the reordering of the conduction and valence bands occurs for the quantum well widths below the theoretical values of critical thickness for InGaN layers pseudomorphically grown on GaN substrates.
12
Content available remote

Resonant Plasmon Response of a Periodically Modulated Two-Dimensional Electron Gas

71%
Sznajder P., Piętka B., Szczytko J., Łusakowski J., Bardyszewski W.
Acta Physica Polonica A
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2012
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vol. 122
|
issue 6
1090-1092
EN
We report the theoretical study of the optical response of a periodically modulated two-dimensional electron gas. The density of states is calculated within the first order of the perturbation theory and the effects of the short-range disorder are explained and discussed. We demonstrate that the magnetic field values corresponding to the characteristic narrowing of the density of states width are given by the zeros of the subsequent Laguerre polynomials. The observed increase of the density of states at the edges are interpreted as van Hove singularities. The broadening effects are shown to modify and smear out the observed effects with increasing temperature above 2 K. The plasmon dispersion relation is discussed in terms of the random phase approximation. Small changes in plasmon dispersion relation related to the periodic modulation were predicted.
13
Content available remote

Spin-Lattice Relaxation Beyond the Debye Approximation

62%
Witowski A., Bardyszewski W., Kutter C., Wyder P., Witkowska B., Mycielski A.
Acta Physica Polonica A
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1995
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vol. 87
|
issue 2
533-535
EN
In this paper we present the results of magnetization relaxation in HgCdMnTe at high magnetic fields. In this mixed crystal the TA phonons have an energy lower than the spin splitting of the Mn^{2+} ground orbital singlet at about 20 T, which allows to check the effect of phonons with wave vectors from the edges of the Brillouin zone on the spin-lattice relaxation.
14
Content available remote

Excitonic Energy Shifts in CdMnTe/CdMgTe Quantum Wells under Resonant Excitation in Presence of 2D Carrier Gas

62%
Trajnerowicz A., Golnik A., Kossacki P., Bardyszewski W., Wiater M., Karczewski G., Wojtowicz T.
Acta Physica Polonica A
|
2008
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vol. 114
|
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.
15
Content available remote

Influence of Impurity Charge Correlation on Free-Carrier Absorption

62%
Szuszkiewicz W., Sobkowicz P., Witkowska B., Bardyszewski W., Julien C., Balkanski M.
Acta Physica Polonica A
|
1993
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vol. 84
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issue 3
559-562
EN
Impurity-mediated free-carrier absorption was analyzed theoretically taking into account the possible spatial impurity correlations. The effect of correlations was included via the structure factor S(q) obtained from finite temperature Monte Carlo simulations of ordering in the impurity system. From the comparison of the experimental data with the results of calculations it is demonstrated that the ordering of charged centers exists for HgSe:Fe in a wide temperature range.
16
Content available remote

Cold and Hot Excitons in CdMnTe/CdMgTe Quantum Wells in Strong Excitation Regime and External Magnetic Field

62%
Trajnerowicz A., Golnik A., Kossacki P., Bardyszewski W., Wiater M., Karczewski G., Wojtowicz T.
Acta Physica Polonica A
|
2009
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vol. 116
|
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.
17
Content available remote

Free-Carrier Plasmons as a Novel Tool in Semiconductor Physics

52%
Szuszkiewicz W., Bardyszewski W., Dingrong Q., Jiaming Z., Julien C., Balkanski M., Witkowska B., Mycielski A.
Acta Physica Polonica A
|
1991
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vol. 79
|
issue 1
141-144
EN
It is demonstrated that free-carrier plasmons being well defined collective excitations of the electron gas in the range of small wave vectors can serve as a sensitive tool to investigate the optical processes related to the small momentum transfers. As an example the system HgSe:Fe is analysed both experimentally and theoretically.
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