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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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  4. 13 Baranowski J.

  5. 13 Kamińska M.

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1
Content available remote

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
Content available remote

Influence of Impact Ionization of Shallow Donors on Luminescence in GaAs

64%
Wysmołek A., Łusakowski J.
Acta Physica Polonica A
|
1995
|
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.
3
Content available remote

Orientation of Metastable EL2 under Uniaxial Stress

64%
Babiński A., Wysmołek A.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 1
137-140
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.
4
Content available remote

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
|
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.
5
Content available remote

Shallow Donors and Acceptors in GaN; Bound Excitons and Pair Spectra

64%
Stępniewski R., Wysmołek A.
Acta Physica Polonica A
|
1996
|
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.
6
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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
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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.
7
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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
|
2017
|
vol. 132
|
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.
8
Content available remote

Hydrostatic Pressure Spectroscopy of the Vanadium Luminescence in GaAs

52%
Wysmołek A., Bożek R., Babiński A., Hennel A.
Acta Physica Polonica A
|
1992
|
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.
9
Content available remote

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
|
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.
10
Content available remote

"Excitonic" and Photoionization Absorption Spectra of Iron in III-V Materials

52%
Wysmołek A., Tryc R., Bożek R., Hennel A.
Acta Physica Polonica A
|
1992
|
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.
11
Content available remote

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.
12
Content available remote

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.
13
Content available remote

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
|
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.
14
Content available remote

Light Induced Modification of Graphene Oxide Layers on GaN Basis

40%
Łopion A., Stobiński L., Pakuła K., Bożek R., Kaźmierczak P., Wysmołek A., Stępniewski R.
Acta Physica Polonica A
|
2016
|
vol. 130
|
issue 5
1169-1171
EN
Graphene oxide suspension in various solvents was spin coated on metal organic vapor phase epitaxy grown GaN/saphire layers. Samples were characterised using the Raman spectroscopy and atomic force microscopy, before and after high temperature treatment. We found that graphene oxide was modifed by high temperature treatment, however a considerable modification was also observed as a result of impinged laser light incident due to the measurements. The Raman spectra were decomposed into two contributions showing different behaviour during the Raman scattering measurements.
15
Content available remote

Strong Photoluminescence Fluctuations in Laser-Thinned Few-Layer WS₂

40%
Bala Ł., Łacińska E., Nogajewski K., Molas M., Wysmołek A., Potemski M.
Acta Physica Polonica A
|
2016
|
vol. 130
|
issue 5
1176-1178
EN
We present results of μ-Raman and μ-photoluminescence study of few-layer WS₂ flakes that have been locally thinned down by a focused laser beam. The Raman spectroscopy measurements prove that the investigated flake was locally thinned down to a monolayer. Interestingly, μ-photoluminescence experiments allowed us to observe huge intensity fluctuations at the boundary of laser-thinned region. Similar effects were found at the edges of a WS₂ bilayer flake, which has not been subjected to laser-thinning. The origin of the observed time evolution of the photoluminescence response is discussed in terms of potential fluctuations resulting from light-induced changes of the charge state of defects.
16
Content available remote

Graphene Based Flow Sensors

40%
Kaźmierczak P., Binder J., Boryczko K., Ciuk T., Strupiński W., Stępniewski R., Wysmołek A.
Acta Physica Polonica A
|
2014
|
vol. 126
|
issue 5
1209-1212
EN
We report on attempts to produce a graphene based liquid flow sensor. Our results indicate that modifications of the electric double layer, formed in the vicinity of the graphene surface, dominate over mechanisms responsible for liquid flow-induced voltage/current generation. Several graphene structures were tested in different measurement configurations, aimed to maximize the generated signal amplitude and its stability. Some realizations of working devices in water as well as in aqueous solutions of NaCl or HCl are presented.
17
Content available remote

Time-Resolved Studies of Gallium Nitride Doped with Gadolinium

40%
Witek B., Wysmołek A., Kamińska M., Twardowski A., Potemski M., Boćkowski M., Grzegory I.
Acta Physica Polonica A
|
2008
|
vol. 114
|
issue 5
1425-1430
EN
Time-resolved photoluminescence experiments on high quality bulk GaN doped with Gd are presented. It was found that the decay time of Gd-related transitions observed for 4.2 K around 1.78 eV is of about 3 ms. Such a long decay time strongly supports the identification of this emission band as due to transitions between Gd³+(4f⁷) levels. The decay time measured for Gd-related transitions observed in the UV spectral range, close to the GaN band-gap, was found to be much faster than 1 μs. This suggests that these emission lines could hardly be correlated with internal transitions within Gd³+(4f⁷). Possible origin of the Gd-related UV luminescence is discussed.
18
Publication available in full text mode
Content available

Emission from Mesoscopic-Size Islands Formed in a GaAs/AlAs Double Layer Structure

40%
Wysmołek A., Chwalisz B., Potemski M., Stępniewski R., Babiński A., Raymond S., Thierry-Mieg V.
Acta Physica Polonica A
|
2004
|
vol. 106
|
issue 3
367-381
EN
The nature of sharp emission lines which are present in macro-luminescence experiments on a type-II GaAs/AlAs double quantum well structure is discussed. The experiments, which also include micro-lumines- cence measurements, allowed us to conclude that the sharp emission lines observed originate from lateral GaAlAs islands of a fewμm in diameter. They serve as efficient type-I recombination centers for indirect excitons and/or carriers which diffuse in the GaAs/AlAs QW structure and strongly affect the emission processes observed in macro-luminescence experiments. These traps can easily be filled with electron-hole pairs, giving rise to the formation of neutral excitons as well as more complex excitonic molecules. Magneto-luminescence spectra from single islands resemble those observed for natural quantum dots formed in narrow GaAs quantum wells.
19
Content available remote

Raman Spectroscopy of Shear Modes in a Few-Layer MoS₂

40%
Gołasa K., Grzeszczyk M., Zinkiewicz M., Nogajewski K., Potemski M., Wysmołek A., Babiński A.
Acta Physica Polonica A
|
2016
|
vol. 129
|
issue 1a
A-132-A-134
EN
We study low frequency vibrational modes in atomically thin molybdenum disulfide (MoS₂) by means of the Raman scattering spectroscopy. A shear mode related to rigid interlayer vibrations is identified. Its energy evolution with the increasing number of layers is well described using a linear chain model with only nearest neighbor interactions. The resulting force constant (Kₓ = 2.7 × 10¹⁹ N/m³) corresponds well to the previously published data.
20
Content available remote

ESR Spectroscopy of Graphene with Adsorbed NaCl Particles

40%
Karpierz E., Drabińska A., Bożek R., Kaźmierczak P., Wysmołek A., Kamińska M., Strupiński W.
Acta Physica Polonica A
|
2014
|
vol. 126
|
issue 5
1187-1189
EN
Due to its peculiar properties graphene is a good candidate for sensor materials. Therefore, it is important to study influence of different fluids on graphene layer. The presented studies showed pinning of NaCl microcrystals to graphene surface after immersing graphene in NaCl solution and subsequent careful rinsing with distilled water. The atomic force microscopy images revealed presence of many NaCl-related structures over 100 nm high on graphene surface. The electron spin resonance spectrum for magnetic field perpendicular to the graphene layer consisted of several lines originating from NaCl. The pinning of NaCl microcrystals resulted in increase of electron scattering, as confirmed by the Raman spectroscopy (the increase of intensity of D and D' bands) and weak localization measurement (the decrease of coherence length).
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