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  1. 109 Acta Physica Polonica A

  2. 1 Biotechnologia

  3. 1 Bulletin of the Polish Academy of Sciences: Technical Sciences

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  4. 13 2011

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  1. 111 Godlewski M.

  2. 25 Guziewicz E.

  3. 24 Monemar B.

  4. 21 Ivanov V.

  5. 18 Witkowski B.

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1
Content available remote

Charge Transfer States of Transition Metal and Rare Earth Ions: Their Role in Recombination Processes

100%
Godlewski M.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 5
849-855
EN
Center ionization accompanied by carrier localization at the center by virtue of a short-range or a long-range Coulomb attractive potential is discussed. The role of charge transfer states in recombination processes is described. The source of carrier attractive potential is explained and a simple theoretical model is presented allowing to predict the nature (either electron or hole attractive) of this potential. The probability of different possible recombination paths is also analyzed.
2
Content available remote

Electroluminescence from Rare Earth Activated Materials - New Concepts

100%
Godlewski M.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 3
435-444
EN
The recent progress in the field of thin film electroluminescence devices is reviewed. The mechanisms responsible for rare earth excitation in high electric field electroluminescence structures are explained. A new mechanism including rare earth ionization is described. Processes limiting electroluminescence efficiency are also discussed.
3
Content available remote

Recombination Processes in ZnSe:Eu

64%
Świątek K., Godlewski M.
Acta Physica Polonica A
|
1991
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vol. 80
|
issue 3
381-384
EN
The photo-ESR and photoluminescence experiments have been performed on high-resistivity ZnSe:Eu crystals. We report the first evidence that the energy level of Eu^{2+} ground state is located within the ZnSe forbidden gap, approximately 2.1 eV below the bottom of the conduction band.
4
Content available remote

Mechanism of Carrier Heating in High Electric Field Electroluminescence Devices

64%
Dedulewicz S., Godlewski M.
Acta Physica Polonica A
|
1992
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vol. 82
|
issue 5
865-867
EN
The mechanism of carrier heating in ZnS-based electroluminescence devices is discussed. We show that carrier acceleration by an applied electric field is at 300 K not a loss-free (ballistic carriers) process. Even for large carrier energies (about 2.5 eV) inelastic scattering on polar optical phonons dominates over elastic scattering on acoustic phonons and ionized impurities.
5
Content available remote

Efficient Two-Center Auger Mechanism of Electron Trapping by Fe^{3+} Ions in ZnSe:Fe,Cr

64%
Surma M., Godlewski M.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 5
1017-1020
EN
A detailed analysis of decay kinetics of light induced electron spin resonance signals of Cr^{1+} and Fe^{3+} ions in ZnSe:Fe,Cr is given. We observe that the Cr^{1+} electron spin resonance signal decays once free electrons are thermally ionized from shallow donors of ZnSe. Such unusual behavior of the Cr^{1+} electron spin resonance signal is explained by efficient two-center Auger recombination: the Cr^{1+} center is ionized due to the Auger-type energy transfer from the electron being trapped by the Fe^{3+} ion. Such process is shown to be consistent with the temperature dependence of the decay times of electron spin resonance signals. Its quantum efficiency is estimated to be as large as 18% for Cr and Fe concentrations which were studied.
6
Content available remote

Carrier Heating Efficiency in Optically Detected Cyclotron Resonance Experiment

64%
Dedulewicz S., Godlewski M.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 3
535-537
EN
Monte Carlo calculations of carrier heating efficiency in optically detected cyclotron resonance experiment are presented. It is shown that electrons accelerated by microwave electric field gain energy sufficient for impact ionization of shallow centers and for exciton dissociation. It is also explained why very sharp thresholds for impact processes were observed in the optically detected cyclotron resonance investigations.
7
Content available remote

Photo-ESR Studies of Ni doped ZnS and ZnSe

52%
Surma M., Zakrzewski A., Godlewski M., Surkova T.
Acta Physica Polonica A
|
1995
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vol. 87
|
issue 1
221-224
EN
The results of electron spin resonance experiments are presented for nickel doped ZnS and ZnSe. Energy level position of Ni^{1+} state in band gap of ZnS and ZnSe is determined. The nonradiative recombination processes of donor-acceptor pairs in Ni doped samples are discussed.
8
Content available remote

The Luminescence and EPR Characterisation of Neutron Transmutation Doped Gallium Phosphide

52%
Gołdys E., Godlewski M., Sienkiewicz A.
Acta Physica Polonica A
|
1991
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vol. 79
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issue 2-3
259-262
EN
The photoluminescence and EPR measurements of neutron irradiated and annealed GaP samples are presented. Both methods confirm the presence of neutral Ge_{Ga}. The EPR spectrum gives also an indication of interstitial Ge.
9
Content available remote

On the Nature of Eu-Related Emissions in ZnS and CaS

52%
Świątek K., Godlewski M., Niinistö L., Leskelä M.
Acta Physica Polonica A
|
1991
|
vol. 79
|
issue 2-3
255-257
EN
The Eu-connected recombination processes in ZnS and CaS are analyzed on the basis of optical studies. A new Eu-related emission in ZnS is attributed to the recombination of an exciton bound at the Eu^{2+} center, while in CaS the emission is dominated by the direct Eu^{2+} intra-ion transition.
10
Content available remote

Recombination Processes for Deep Impurity States Degenerate with the Conduction Band

52%
Świątek K., Godlewski M., Kaliński Z., Przybylińska H.
Acta Physica Polonica A
|
1991
|
vol. 79
|
issue 2-3
243-246
EN
We report on the studies of autoionization efficiency and the relevant recombination mechanism for Eu^{2+} in Ca_{x}Cd_{1-x}F_{2} depending on the energy level position of Eu^{2+} excited states in respect to the conduction band states.
11
Publication available in full text mode
Content available

Luminescence of Cd0.7Mn0.3Te Crystals in Transverse Magnetic Field

52%
Brazis R., Barauskaitė L., Ivanov V., Godlewski M.
Acta Physica Polonica A
|
2006
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vol. 109
|
issue 6
731-741
EN
Photoluminescence of cleaved Cd0.7Mn0.3Te crystals is studied at T≈1.6 K at the normal- and oblique (45º) incidence of the pumping Ar laser beam (λ=488 nm) in magnetic fields -7≤ B≤7 T in the Voigt geometry. At B=0, photoluminescence maximum is found at 2.0819 eV at normal incidence (and backward emission) whereas the oblique incidence and emission shows photoluminescence maximum intensity at 2.0536 eV. The red shift of photoluminescence maximum position with the rise in B is observed and the results are found to be in good agreement with sp-d exchange interaction model for the oblique incidence case. Backward emitted photoluminescence line is found to narrow from 26.2 to 23.5 meV with the rise in B from 0 to 7 T. Alloy disorder contribution exhibits opposite trend to broaden, as is calculated on the basis of the matrix of the energy gap dependence on x and B. Therefore the observed photoluminescence line narrowing is assigned to the suppression of magnetic fluctuation in magnetic field. A linear size of magnetic fluctuation is estimated to be about 1/5 of the free exciton diameter. Photoluminescence maximum position difference in the normal- and oblique incidence cases is assigned to polaritons.
12
Content available remote

Optical Properties of Molecular Beam Epitaxy Grown ZnSe on GaAs

52%
Karpińska K., Suchocki A., Godlewski M., Hommel D.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 3
551-554
EN
Photoluminescence studies of molecular beam epitaxy grown ZnSe-on-GaAs layers are presented. The high sensitivity of the PL technique allowed for identification unintentional dopants in pure ZnSe sample. Characteristic photoluminescence lines due to extended defects were observed. The experimental results obtained show a correlation between intentional doping level and extended defects concentration. We conclude also that even though molecular beam epitaxy layers are grown at low temperature, the self-compensation mechanism may still be important. For heavily doped sample edge emission is deactivated likely due to efficient energy transfer link with deep donor-acceptor pair bands.
13
Content available remote

Bistable Behaviour of the New Shallow Thermal Donor in Aluminum Doped Silicon

52%
Kaczor P., Godlewski M., Gregorkiewicz T.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 3
555-558
EN
In the present study a new bistable shallow thermal donor in aluminum doped silicon was investigated by means of the Fourier transform infrared spectroscopy. The temperature dependence of the photo-conversion into the metastable state was established and some Hints for the origin of the metastability were given.
14
Content available remote

Comparison of Microscopic Mechanisms of Blue Anti-Stokes Luminescence in Undoped and Chromium Doped ZnSe Crystals

52%
Ivanov V., Omel'chuk A., Godlewski M.
Acta Physica Polonica A
|
1998
|
vol. 94
|
issue 3
365-368
EN
Anti-Stokes luminescence is observed in chromium doped and in undoped ZnSe crystals. In the former case anti-Stokes luminescence is due to two complementary ionization transitions of Cr ions. In the latter case two-photon absorption becomes important at a high excitation density.
15
Content available remote

Influence of Magnetic Field on Blue Anti-Stokes Luminescence of ZnSe:Cr Crystals

52%
Ivanov V., Semenov Y. G., Surma M., Godlewski M.
Acta Physica Polonica A
|
1996
|
vol. 90
|
issue 4
821-824
EN
The results of photoluminescence and magneto-luminescence studies of chromium doped ZnSe crystals are presented for blue colour shallow donor-shallow acceptor pair photoluminescence, with a zero phonon line at 2.692 eV. This donor-acceptor pair photoluminescence is observed under photo-excitation with photon energies smaller than the emission energy (anti-Stokes luminescence) and dominates in the photoluminescence spectrum of ZnSe:Cr at the excitation energy about 2.41 eV and for temperature T<20 K. A quantum efficiency of this anti-Stokes luminescence is relatively large. It is of about 10^{-3} at 0 T and increases with increasing magnetic field up to 7 T at temperature T=2 K. We relate the intensity of the anti-Stokes luminescence to a non-equilibrium concentration of photo-excited Cr^{+} ions and propose that the rate of spin-dependent recombination of Cr^{+} ions with free holes (decreases with increasing magnetic field) is responsible for the observed increase in the anti-Stokes luminescence intensity at higher magnetic fields.
16
Content available remote

Enhanced Exciton-Phonon Interaction in Strained ZnCdSe/ZnSe Quantum Well Structures

52%
Godlewski M., Leonardi K., Hommel D.
Acta Physica Polonica A
|
1997
|
vol. 92
|
issue 4
769-773
EN
Radiative recombination processes in pseudomorphic ZnCdSe/ZnSe structures are compared to those observed in strain-relaxed structures grown on GaAs substrates with thick ZnSe buffer layers. From the temperature dependence of the photoluminescence line width we evaluate the strength of exciton-phonon interaction with acoustic (dominant at lower temperatures) and optical phonons. Stronger exciton-phonon interaction is observed for pseudomorphic structures. Such enhanced exciton-phonon interaction is likely responsible for a faster photoluminescence deactivation at increased temperatures. We also report different exciton properties (photoluminescence intensity, width, strength of exciton-phonon interaction) in quantum well of a given width but in structures grown with different order of quantum wells. More stable photoluminescence (with increasing temperature) is observed for a given quantum well if it is closer to the buffer layer and not to the cap layer.
17
Content available remote

Morphology and Optical Properties of Laser-Assisted Chemical Vapour Deposited GaN

52%
Goldys E., Godlewski M., Tansley T.
Acta Physica Polonica A
|
1998
|
vol. 94
|
issue 2
331-335
EN
Properties of GaN epilayers grown by laser-assisted chemical vapour deposition are discussed. Good crystallinity and surface morphology of the films is demonstrated. Micro-Raman spectra are explained by scattering by small, randomly oriented cubic phase units present in the GaN film.
18
Content available remote

Band Edge Energies Pinning in Magnetic Field in Semimagnetic Cd_{0.7}Mn_{0.3}Te

52%
Barauskaitė L., Brazis R., Ivanov V., Godlewski M.
Acta Physica Polonica A
|
2011
|
vol. 120
|
issue 6
1056-1060
EN
Results of Cd_{0.7}Mn_{0.3}Te magneto-photoluminescence investigations are analyzed. Photoluminescence was measured in a Voigt geometry at the temperature of 1.6 K. Two models describing radiative transition energy are compared with the experimental results of Cd_{0.7}Mn_{0.3}Te luminescence. The energy of recombination transition, employing the complete form of band states splitting description (term due to the Landau splitting included), shows deviation from experiment at B > 2 T. Two possible reasons of discrepancies from the experiment - exchange interaction constants dependence on magnetic field or band edge energies pinning in magnetic field - are discussed. Band edge energies pinning in magnetic field is related to the hybridization of Mn 3 d^{5} levels with the band states of the host. We determine the corrected values of exchange interaction constants (N_0 α -N_0 β/3) at magnetic fields B < 5 T.
19
Content available remote

Influence of Annealing on Optical Properties of ZnO Nanorods Obtained by the Microwave-Assisted Hydrothermal Process

52%
Materska P., Witkowski B., Godlewski M.
Acta Physica Polonica A
|
2016
|
vol. 130
|
issue 5
1202-1204
EN
Optical properties of ZnO nanorods (of different sizes, grown on two different substrates) are investigated. Nanorods were grown using microwave-assisted hydrothermal process on gallium nitride or silicon substrate. To initiate nanorods growth on a silicon substrate ZnO nucleation layer was used. ZnO nanoseeds were deposited by atomic layer deposition. For GaN substrate an epitaxial relation was observed. For both substrates nanorods show a hexagonal structure, expected for wurtzite ZnO. Results of nanorods annealing are discussed.
20
Publication available in full text mode
Content available

Electronic Structure of ZnS:Co Semiconductors: X-ray and Optical Spectroscopy Studies

52%
Surkova T., Galakhov V., Godlewski M.
Acta Physica Polonica A
|
2003
|
vol. 103
|
issue 6
703-708
EN
Experimental studies of X-ray photoelectron and Co L_α X-ray emission spectra of the ZnS:Co semiconductor were carried out. It was established that Co ions are in a Co^{2+} configuration and that the Co 3d impurity states are localized above the top of the valence band by 1.0±0.2 eV.
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