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  1. 47 Acta Physica Polonica A

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  1. 47 Wysmołek A.

  2. 20 Stępniewski R.

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1
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Magnetized Plasma in Polar Semiconductors

100%
Wysmołek A.
Acta Physica Polonica A
|
2007
|
vol. 112
|
issue 2
141-152
EN
Plasma excitations in metallic n-type GaAs are studied in high-magnetic fields using the method of inelastic light scattering (the Raman scattering). Experimental data are analyzed using a standard, dielectric function theory. The results obtained for samples with a high electron concentration are well understood in terms of longitudinal excitations. A strong interaction of coupled longitudinal optical-phonon-plasmon modes with the collective cyclotron resonance excitations (the Bernstein modes) is observed. In samples with a lower electron concentration, the unexpected feature in the vicinity of the undressed optical phonon is observed at high magnetic fields. This effect is explained in terms of transverse excitations, which would appear in the Raman spectrum due to disorder-activated selection-rule breaking. A field induced metal-insulator transition and magnetopolaron effect on shallow donors in GaAs is shown to be traced with the Raman scattering experiments in samples with the lowest electron concentration.
2
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Shallow Donors and Acceptors in GaN; Bound Excitons and Pair Spectra

64%
Stępniewski R., Wysmołek A.
Acta Physica Polonica A
|
1996
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vol. 90
|
issue 4
681-690
EN
Recent photoluminescence results obtained for homoepitaxial GaN layers are presented. Dominant photoluminescence structures observed for these layers can be assigned to excitons bound to neutral impurities. Different methods such as temperature dependent evolution, high magnetic field and time resolved spectroscopy have been used to study the exciton line properties. For the p-type samples sharp lines are observed, assigned to the donor-acceptor recombination for differently distant pairs. The analysis of the optical transitions related to donors and acceptors is in reasonable agreement with the effective mass approximation. Electron phonon interaction was found to strongly affect the optical properties of GaN. The dominant intrinsic defect has been identified as a donor located at a nitrogen site.
3
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Electrical Properties of an Acceptor-like State of Metastable EL2 in n-type GaAs under Uniaxial Stress

64%
Babiński A., Wysmołek A.
Acta Physica Polonica A
|
1992
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vol. 82
|
issue 5
908-910
EN
The electrical resistivity and deep level transient spectroscopy measurements of n-type GaAs under uniaxial stress for [100] and [111] directions at low temperatures are presented. After the transformation of EL2 to its metastable state the stress induced strong anisotropy in the increase in resistivity was observed. The observed splitting of the acceptor-like state of metastable EL2 implies the trigonal symmetry of that defect.
4
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Influence of Impact Ionization of Shallow Donors on Luminescence in GaAs

64%
Wysmołek A., Łusakowski J.
Acta Physica Polonica A
|
1995
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vol. 87
|
issue 1
261-264
EN
Luminescence spectra of n-type molecular beam epitaxial layer and semi-insulating liquid encapsulated Czochralski grown bulk GaAs were mea­sured at liquid helium temperature for zero electric field and for fields which caused impact ionization of shallow donors. Application of the electric field caused a decrease in the luminescence intensity and a broadening of all ob­served structures. It was found that the electric field changed the lumines­cence spectrum of the n-type material in a different way than it did in the case of the semi-insulating one. For the n-type sample, an intensity of exci­tonic lines decreased much more than that of donor-acceptor lines when the electric field grew. A contrary was observed for the semi-insulating sample. An explanation of the result is proposed which takes into account an in­fluence of ionised impurity scattering and localization in fluctuations of the electrostatic potential on the luminescence process.
5
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Orientation of Metastable EL2 under Uniaxial Stress

64%
Babiński A., Wysmołek A.
|
EN
Results of electrical resistivity and Hall measurements of n-type GaAs under uniaxial stress along [111] direction performed at low temperature are presented. Alter the transformation of the EL2 defect into its metastable configuration, a stress-induced increase in electrical resistivity related to the capture of electrons by the acceptor state of the metastable EL2([EL2*]^{-/0}) was observed. It was found that the stress-induced increase in resistivity depended on the method of EL2-photoquenching. The observed effects are explained as the reorientation of EL2* centers in the crystal. The stress coefficients of the triple degenerate and the single degenerate sublevels of the [EL2*]^{-/0} are found to be equal to -17 meV/GPa and -41 meV/GPa.
6
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In Situ Raman Spectroscopy of Solution-Gated Graphene on Copper

52%
Binder J., Stępniewski R., Strupiński W., Wysmołek A.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
360-363
EN
We present a solution-gated in situ Raman spectroscopy approach, which enables the electrical characterization of graphene on a copper substrate without the need of a transfer process. The application of a voltage across the solution resulted in a shift of the Raman G-band without a significant shift of the 2D band. This observation allowed for the separation of the effects of strain and doping. Based on the G and 2D band shifts we show that we can manipulate the n-type carrier concentration of graphene directly on the copper substrate in a range from about 8× 10¹² cm¯² to about 1.5× 10¹³ cm¯².
7
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Hydrostatic Pressure Spectroscopy of the Vanadium Luminescence in GaAs

52%
Wysmołek A., Bożek R., Babiński A., Hennel A.
Acta Physica Polonica A
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1992
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vol. 82
|
issue 5
837-840
EN
We report luminescence measurements of the intracenter transition ^{3}T_{2} → ^{3}A_{2} of the V^{3+}(3d^{2}) charge state in semi-insulating GaAs under hydrostatic pressure up to 0.8 GPa at liquid helium temperature. The hydrostatic pressure coefficient of the zero-phonon line is found to be equal to 6.9 ± 0.2 meV/GPa. This result enables us to determine the Huang-Rhys parameter, which characterizes the coupling to the symmetric mode of vibration, as S_{A} = 1.4 ± 0.1. Using this parameter, computer simulation leading to a reconstruction of the shape of both luminescence and corresponding absorption spectra were performed.
8
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Origin of Centres Involved in Blue and Orange Luminescence of 6H-SiC

52%
Wysmołek A., Baranowski J. M., Kamińska M.
Acta Physica Polonica A
|
1995
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vol. 88
|
issue 5
957-960
EN
We present new results of luminescence of n-type 6H-SiC crystals. We have found two shallow donors with ionization energies at 60 meV and 140 meV. We have shown that the blue luminescence is not affected by the ionization of the shallower donor and is related to deeper donor which we attribute to N at C-site. We propose that the origin of the more shallower donor at 60 meV is related to carbon vacancy. We have found that the intensity of the orange luminescence increases under infrared illumination. This result confirms that the orange luminescence is due to conduction band-deep centre transitions. We believe that deep centre responsible for the orange luminescence is the silicon vacancy.
9
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"Excitonic" and Photoionization Absorption Spectra of Iron in III-V Materials

52%
Wysmołek A., Tryc R., Bożek R., Hennel A.
Acta Physica Polonica A
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1992
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vol. 82
|
issue 5
911-913
EN
We report optical absorption measurements of Fe-doped GaAs, InP and GaP crystals obtained with the help of different doping techniques. In all these crystals photoionization spectra corresponding to Fe^{3+} → Fe^{2+} transitions with sharp "excitonic" lines were observed. The intensities of these lines are not proportional to the intensities of photoionization absorption bands, i.e. to the concentration of the Fe^{3+} centers. Variation of more than one order of magnitude was observed for different semiconductors and for different crystals of the same material. These results suggest that only some iron centers are responsible for the "excitonic" spectra.
10
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Deep Level Transient Spectroscopy Measurements of an Acceptor-like State of Metastable EL2 in GaAs and GaAsP

52%
Babiński A., Wysmołek A., Słupiński T.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 4
673-676
EN
The results of deep level transient spectroscopy measurements of an acceptor-like state of metastable EL2 in GaAs and GaAs_{0.97}P_{0.03} are presented. The uniaxial stress in GaAs was applied in order to find the deep leve1 transient spectroscopy signal. It was found that the deep level transient spectroscopy signal depended on the stress direction. In GaAs_{0.97}P_{0.03} the deep level transient spectroscopy peak related to an acceptor-like state of metastable EL2 was observed without external stress.
11
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Transmission Electron Microscopy and Luminescence Studies of Quantum Well Structures Resulting from Stacking Fault Formation in 4H-SiC Layers

46%
Borysiuk J., Wysmołek A., Bożek R., Strupiński W., Baranowski J.
Acta Physica Polonica A
|
2008
|
vol. 114
|
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.
12
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Competition of Radiation Processes in 6H-SiC Observed by Luminescence

46%
Wysmołek A., Mroziński P., Dwiliński R., Vlaskina S., Kamińska M.
Acta Physica Polonica A
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1995
|
vol. 87
|
issue 2
437-440
EN
We report on the results of photoluminescence and thermoluminescence measurements of various 6H-SiC crystals. At low temperature in all n-type samples two bands with maxima at 2.7 eV (blue) and 1.8 eV (orange) were detected. In the p-type material only blue band was observed. The mea­surements performed at a broad range of temperatures showed totally dif­ferent behaviour of photoluminescence intensity of both bands. The pre­sented results could be explained in the model assuming well established donor-acceptor pair recombination for the blue band emission and the con­duction band - deep defect transition for the orange band. The proposed model was confirmed by thermoluminescence measurements of the orange band which showed peaks at 30 K, 80 K, 100 K, 150 K attributed to ioniza­tion of subsequent shallow donor levels.
13
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Time Resolved Magnetophotoluminescence of Biased GaAs/AlGaAs Double Quantum Well Structure

46%
Surowiecka K., Wysmołek A., Stępniewski R., Potemski M., Henini M.
Acta Physica Polonica A
|
2008
|
vol. 114
|
issue 5
1369-1374
EN
Time resolved photoluminescence of double quantum well structure was investigated versus electric and magnetic fields applied across the sample. The emission due to direct excitons (electron and hole are localized within the same quantum well) decays fast at the nanosecond timescale, whereas the recombination kinetics of indirect excitons is much slower and spreads over microseconds. The time evolution of indirect exciton emission is shown to be altered by application of either electric or magnetic field. This reflects the non-trivial effects of exciton localization which leads to the non-exponential decays of the indirect exciton emission.
14
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Content available

Magneto-Luminescence Study of Silicon-Vacancy in 6H­Si

40%
Wysmołek A., Wardak K., Stępniewski R., Baranowski J., Potemski M., Tymicki E., Grasza K.
Acta Physica Polonica A
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2006
|
vol. 110
|
issue 3
437-442
EN
The magneto-spectroscopy studies of luminescence related to silicon-vacancy, in high quality 6H-SiC crystals grown by the seeded physical vapor transport method, are presented. The superior optical quality of these crystals allowed us to resolve a doublet structure of the 1.398 eV emission line (V_2 line), commonly assigned to the transitions involving two singlet states of the silicon-vacancy. Experiments performed in magnetic fields up to 20 T showed that each doublet constituent of the V_2 line splits into four components for the magnetic field parallel to the c-axis of the 6H-SiC crystals. This result could be hardly explained in terms of a singlet to singlet transition. The analysis of the angle-resolved luminescence experiments in high magnetic fields serves us to discuss the symmetry of the defect states responsible for the V_2-line in silicon carbide.
15
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Absorption and Emission Properties of Light Emitting Diode Structures Containing GaInN/GaN QWs

40%
Binder J., Korona K., Borysiuk J., Wysmołek A., Baeumler M., Köhler K., Kirste L.
Acta Physica Polonica A
|
2011
|
vol. 120
|
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.
16
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Anharmonic Optical Phonon Effects in ZnO Nanocrystals

40%
Khusnutdinov S., Dynowska E., Zaleszczyk W., Makhniy V., Wysmołek A., Korona K.
Acta Physica Polonica A
|
2011
|
vol. 119
|
issue 5
678-680
EN
Zinc oxide (ZnO) is a very promising material for optoelectrical devices operating at the short-wavelength end of the visible spectral range and at the near UV. The Raman scattering studies of ZnO heterolayers formed by isothermal annealing show sharp phonon lines. In addition to the A_1(TO), E_1(TO), E_2^{H}, and E_1(LO) one-phonon lines, we observed two-phonon lines identified as: E_2^{H} - E_2^{L}, E_2^{H} + E_2^{L}, and 2LO at 332, 541, and 1160 cm^{-1}, respectively (at room temperature). The identification of the E_2^{H} - E_2^{L} peak was confirmed by its thermal dependence. Temperature dependent measurements in the range 6-300 K show that the phonon frequencies decrease with temperature. The E_2^{H} peak is at energy 54.44 meV (439.1 cm^{-1}), at 4 K and due to phonon-phonon anharmonic interaction, its energy decreases to 54.33 meV (438.2 cm^{-1}) at room temperature. The Grüneisen parameter found for this oscillation mode was γ_{E} 2H = 1.1 at about 300 K. The intensity of the E_2^{H} - E_2^{L} peak increases strongly with temperature and this dependence can be described by the Bose-Einstein statistics with activation energy of 13.8 meV (nearly equal to the energy of the E_2^{L} phonon).
17
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Optical and Electrical Measurements of Low-Temperature InAlAs

40%
Korona K., Wysmołek A., Bożek R., Kamińska M., Baranowski J., Weber E.
Acta Physica Polonica A
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1992
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vol. 82
|
issue 5
825-828
EN
Photoluminescence, photocurrent, thermally stimulated current and photoinduced current transient spectroscopy measurements done on molecular beam epitaxy In_{0.52}Al_{0.48}As layer, lattice matched to InP are reported. The investigated layers were grown on semi-insulating InP wafers, at temperature range from 215 to 450°C. It was found that the Fermi level was pinned to a dominant midgap center (most likely similar to EL2 center). Moreover, there were at least 7 other defects but with much smaller concentrations. Their activation energies were equal to 0.076, 0.11, 0.185, 0.295, 0.32 and 0.40 eV. The layers exhibited a very low luminescence and a small photocurrent.
18
Publication available in full text mode
Content available

Carriers Diffusion in GaAs/AlAs Type II Quantum Well

40%
Lesiak A., Chwalisz B., Wysmołek A., Potemski M., Stępniewski R., Thierry-Mieg V.
Acta Physica Polonica A
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2005
|
vol. 108
|
issue 5
755-760
EN
The micro-photoluminescence of GaAs/AlAs type II double quantum well structure is presented. The specific band alignment of the investigated system allows obtaining high concentration of long lived carriers. This enables us to study diffusion of carriers and/or indirect excitons. It was found that the carrier flow does not follow the classical diffusion equation and is driven by the potential modification due to the presence of photo created carriers.
19
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Optical and Electrical Studies of FR1 and FR2 Defects in GaAs

40%
Dwiliński R., Palczewska M., Kaczor P., Korona K., Wysmołek A., Bożek R., Kamińska M.
Acta Physica Polonica A
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1992
|
vol. 82
|
issue 4
613-616
EN
The systematic EPR, optical absorption, photoluminescence and thermally stimulated current studies of acceptor defects in bulk GaAs were performed. For the first time, parallel EPR and optical absorption experiments allowed to find the absorption spectrum due to the photoionization of FR1 defect with the threshold at 0.19 eV. Photoluminescence studies showed two families of bands in the energy range of about 1.25 to 1.35 eV. We tentatively ascribed them to FR1 and FR2 complexes with shallow donors. Thermally stimulated current measurements showed two peaks at 90 K and 110 K assigned to FR1 and FR2 respectively.
20
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Built-In Electric Field in High Quality GaN/AlGaN Quantum Wells

40%
Zieleniewski K., Pakuła K., Bożek R., Masztalerz K., Wysmołek A., Stępniewski R.
Acta Physica Polonica A
|
2011
|
vol. 119
|
issue 5
657-659
EN
We report studies on electric field built in GaN/Al_{0.09}Ga_{0.91}N structure of nominally 6 nm wide quantum well. The sample was grown in horizontal metal-organic chemical vapor deposition reactor using innovative technology that decreases the density of screw dislocations. Firstly, using visible and mid infra-red interference pattern along the sample, the layer thickness and consequently the quantum well width was determined to vary linearly with the position. Secondly, photoluminescence spectra was taken at different positions. Correlation of those two measurements allows us to determine the built-in electric field to be 0.66 MV/cm, which is considerably larger than previously reported for similar structures.
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