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  1. 25 Acta Physica Polonica A

  2. 1 Biotechnologia

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  1. 26 Porowski S.

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  3. 10 Suski T.

  4. 9 Leszczyński M.

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1
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High Pressure Crystallization of III-V Nitrides

100%
Porowski S.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
295-302
EN
Crystal growth from the solution under high N_{2} pressure (HNP method) results in high quality mm size crystals of GaN in 5 to 24 hour process. The crystallization of AlN is less efficient due to relatively lower solubility of nitrogen in the liquid Al. Possibility of InN growth is strongly limited since this compound is unstable at T > 600°C even at 20 kbar. The growth of cm size high quality GaN crystals requires lower supersaturations and longer processes.
2
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Influence of Electric Field on Recombination Dynamics of Quantum Confined Carriers

52%
Korona K., Borysiuk J., Skierbiszewski C., Porowski S.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
243-247
EN
We present time-resolved photoluminescence measurements of GaN/AlGaN low dimensional structures showing very characteristic changes of dynamics related to strong electric field. Strong piezoelectric and spontaneous polarizations built-in in nitride structures lead to the changes in spatial separation of carriers which leads to changes in recombination energies and radiative lifetimes of the carriers. The observed effect can be well described by a simple exponential relation. The observed dependence can be explained by an approximated model of quantum-confined Stark effect based on the Airy functions.
3

Application of high pressure in food technology and medicine

46%
Wandel A., Gensler I., Porowski S., Jurczak J., Barciszewski J.
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issue 1
199-211
EN
For the first time, high pressure was used for milk sterilization at the beginning of this century. However, only recently attention has been paid to this method and its possible applications in food preservation and inactivation of some viruses. In this review, we summarize high pressure effects on biological macromolecules such as proteins, nucleic acids, ribosomes and other cell components. We also show examples of practical application of high pressure in food conservation and medicine.
4
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The Application of High Pressure in Physics and Technology of III-V Nitrides

39%
Grzegory I., Leszczyński M., Krukowski S., Perlin P., Suski T., Porowski S.
Acta Physica Polonica A
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2001
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vol. 100
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issue Supplement
57-109
EN
Due to high bonding energy of N_2 molecule, the III-V semiconducting nitrides, especially GaN and InN require high N_2 pressure to be stable at high temperatures necessary for growth of high quality single crystals. Physical properties of GaN-Ga(l)-N_2 system are discussed in the paper. On the basis of the experimental equilibrium p-T-x data and the quantum-mechanical modeling of interaction of N_2 molecule with liquid Ga surface, the conditions for crystallization of GaN were established. The crystals obtained under high pressure are of the best structural quality, having dislocation density as low as 10-100 cm^{-2} which is several orders of magnitude better than in any other crystals of GaN. The method allows to grow both n-type substrate crystals for optoelectronics and highly resistive crystals for electronic applications. The physical properties of the pressure grown GaN measured to characterize both point defects and extended defects in the crystal lattice are discussed in the paper. A special attention is paid to the application of high pressure to reveal the nature of the point defects in the crystals and electric fields in GaN-based quantum structures. Due to their very high structural quality, the pressure grown crystals are excellent substrates for epitaxial growth of quantum structures. It opens new possibilities for optoelectronic devices, especially short wavelength high power lasers and efficient UV light emitting diodes. This is due to the strong reduction in dislocation densities in relation to existing structures (10^6-10^8 cm^{-2}) which are grown on strongly mismatched sapphire and SiC substrates. The experimental results on the epitaxial growth and physical properties of GaN-based device structures supporting above conclusions are discussed in the paper. The current development of blue laser technology in High Pressure Research Center is shortly reviewed.
5
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Observation of Magnetic Anisotropy in Bulk GaMnN:Mg Crystals

39%
Gosk J., Zając M., Kamińska M., Twardowski A., Grzegory I., Boć M., Porowski S.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
665-669
EN
Magnetic properties of bulk wurtzite n-type GaMnN and highly resistive GaMnN:Mg monocrystals were studied for the magnetic field applied parallel and perpendicular to the crystal hexagonal c-axis. Magnetization of both types of samples reveals paramagnetic behavior. However, for n-type GaMnN isotropic magnetization was observed which is in agreement with Mn d^5 configuration. On the other hand, GaMnN co-doped with Mg shows large magnetic anisotropy which suggests Mn to be in nonspherical d^4 or d^3 configuration.
6
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Crystallographic Properties of Bulk GaN Crystals Grown at High Pressure

39%
Leszczyński M., Grzegory I., Bockowski M., Jun J., Porowski S., Jasiński J., Baranowski J. M.
Acta Physica Polonica A
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1995
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vol. 88
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issue 4
799-802
EN
Gallium nitride bulk crystals grown at about 15 kbar and 1500 K have been examined by using the high resolution X-ray diffractometry. An anal­ysis of a set of the rocking curves of various Bragg reflections enabled us to estimate a dislocation density. For the crystals of dimensions lower than about 1 mm it is lower than 10^{-5} cm^{-2}. For bigger samples the crystallo­graphic quality worsens. With an application of the reciprocal lattice map­ping we could distinguish between internal strains and mosaicity which are both present in these crystals The results for the bulk crystals are compared with those for epitaxial layers.
7
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Luminescence Dynamics of Exciton Replicas in Homoepitaxial GaN Layers

39%
Korona K., Baranowski J., Pakuła K., Monemar B., Bergman J., Grzegory I., Porowski S.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
841-844
EN
Photoluminescence of excitons and their phonon replicas in homoepitaxial MOCVD-grown gallium nitride (GaN) layers have been studied by picosecond (ps) time-resolved photoluminescence spectroscopy. The time-resolved photoluminescence spectroscopy has shown that the free excitons and their replicas have the fastest dynamics (decay time of about 100 ps). Then, the excitons-bound-to-donors emission rises (with the rise time similar to the free excitons decay time) and decays with t=300 ps. The excitons-bound-to-acceptors has the slowest decay (about 500 ps). It has been found that the ratio of excitons-bound-to-acceptors and excitons-bound-to-donors amplitudes and their decay times are different for 1-LO replicas and then for zero-phonon lines, whereas the ratio of amplitudes and the decay time of the 2-LO replicas are similar to the ones of the zero-phonon lines.
8
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High Pressure Freeze-out of Electrons in Undoped GaN Crystal. Proof of Existence of Resonant Donor State (Nitrogen Vacancy)

39%
Perlin P., Teisseyre H., Suski T., Leszczyński M., Grzegory I., Jun J., Porowski S.
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EN
We investigated free carriers related optical absorption in GaN in hy­drostatic pressures up to 30 GPa. The disappearance of this absorption at pressures close to 18 GPa was explained by trapping electrons resulting from the shift of nitrogen vacancy related donor level into the GaN energy gap at high pressure. We estimated the energetic position of this level at atmo­spheric pressure to be about 0.8 eV above the conduction band minimum.
9
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Two-Electron Transition in Homoepitaxial GaN Layers

39%
Fiorek A., Baranowski J., Wysmołek A., Pakuła K., Wojdak M., Grzegory I., Porowski S.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
742-744
EN
It is shown that the luminescence mapping is a powerful method to help identify optical transitions. Two-electron transition was identified in the homoepitaxial GaN layer by this technique. It was found that the donor and acceptor bound exciton emissions are spatially displaced and show intensity maxima at different places of the epitaxial layer. It was also found that the 3.45 eV line, suspected as "two-electron transition", follows exactly the donor bound exciton spatial distribution. Donor bound exciton recombines leaving the neutral donor in the excited 2s state. Thus, 1s-2s excitation being equal to 22 meV corresponds to 29 meV hydrogenic donor binding energy. This is the first identification of the two-electron transition in GaN.
10
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Measurement of Very Small Zeeman Splittings in GaN:Mn,Mg by Faraday Rotation

33%
Wołoś A., Kossacki P., Golnik A., Kamińska M., Gaj J., Twardowski A., Grzegory I., Boćkowski M., Porowski S.
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issue 4-5
695-699
EN
In this work we demonstrate an application of Faraday rotation for measuring an extremely small Zeeman splitting of an Mn related absorption line placed at 1.417 eV in optical absorption spectrum of Mn and Mg doped gallium nitride. Analysis of the collected spectra allowed us to determine the value of the splitting as equal to 0.12±0.01 meV at 6 T. This data should help in establishing the nature of the observed absorption band.
11
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Coupling of LO Phonons to Excitons in GaN

33%
Wysmołek A., Łomiak P., Baranowski J., Pakuła K., Stępniewski R., Korona K., Grzegory I., Boćkowski M., Porowski S.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
981-984
EN
The photoluminescence of homoepitaxial and heteroepitaxial GaN layers is reported. It is shown that the coupling between LO phonons and neutral acceptor bound excitons is much stronger than the coupling between LO phonons and neutral donor bound excitons. In undoped homoepitaxial layer, in spite of that the no-phonon emission due to donor bound excitons is one order of magnitude stronger than the acceptor bound excitons emission, the predominant structure in the LO phonon replica of the excitonic spectrum is related to optical transitions involving acceptor bound excitons. Temperature studies showed that at higher temperature the LO phonon replica is related to free excitons.
12
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MnAs Overlayer on GaN(000_1)-(1 x 1) - Its Growth, Morphology and Electronic Structure

33%
Kowalski B., Kowalik I., Iwanowski R., Łusakowska E., Sawicki M., Sadowski J., Grzegory I., Porowski S.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
645-650
EN
MnAs layer has been grown by means of MBE on the GaN(000_1)-(1 x 1) surface. Spontaneous formation of MnAs grains with a diameter of 30-60 nm (as observed by atomic force microscopy) occurred for the layer thickness bigger than 7 ML. Ferromagnetic properties of the layer with Curie temperature higher than 330 K were detected by SQUID measurements. Electronic structure of the system was investigated in situ by resonant photoemission spectroscopy for MnAs layer thickness of 1, 2, and 8 ML. Density of the valence band states of MnAs and its changes due to the increase in the layer thickness were revealed.
13
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Growth of GaN Metalorganic Chemical Vapour Deposition Layers on GaN Single Crystals

33%
Pakula K., Baranowski J. M., Stępniewski R., Wysmołek A., Grzegory I., Jun J., Porowski S., Sawicki M., Starowieyski K.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
861-864
EN
The homoepitaxial growth of GaN layers has been achieved for the first time. Bulk GaN single crystals which have been used as a substrate have been grown from diluted solution of atomic nitrogen in the liquid gallium at 1600°C and at nitrogen pressure of about 15-20 kbar. It is shown that a terrace growth of GaN epitaxial layer has been realized. The high quality of the GaN film has been confirmed by luminescence measurements. The analysis of donor-acceptor and exciton luminescence is presented.
14
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Epitaxial Layers Versus Bulk Single Crystals of GaN. Temperature Studies of Lattice Parameters and Energy Gap

33%
Teisseyre H., Perlin P., Leszczyński M., Suski T., Dmowski L., Grzegory I., Porowski S., Jun J., Moustakas T.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
403-406
EN
Gallium nitride epitaxial layer grown by molecular beam epitaxy and bulk crystal grown at high pressure were examined by using X-ray diffrac­tion methods, and by optical absorption at a wide temperature range. The free electron concentration was 6 × 10^{17} cm^{-3} for the layer and about 5 × 10^{19} cm^{-3} for the bulk crystal. The experiments revealed a different po­sition of the absorption edge and its temperature dependence for these two kinds of samples. The structural examinations proved a significantly higher crystallographic quality of the bulk sample. However, the lattice constants of the samples were nearly the same. This indicated that a rather different electron concentration was responsible for the different optical properties via Burstein-Moss effect.
15
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III-V Semiconducting Nitrides Energy Gap under Pressure

33%
Perlin P., Gorczyca I., Teisseyre H., Suski T., Litwin-Staszewska E., Porowski S., Grzegory I., Christensen N.
Acta Physica Polonica A
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1992
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vol. 82
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issue 4
674-676
EN
In this paper we present overview of our recent experimental and theoretical results concerning electronic band structure of III-V nitrides under pressure. It is shown here that the pressure coefficients of the direct gap for studied nitrides are surprisingly small. To describe tendency in changes of the gap with pressure we use a simple empirical relation.
16
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Mn Impurity in GaN Studied by Electron Paramagnetic Resonance

33%
Wołoś A., Palczewska M., Wilamowski Z., Kamińska M., Twardowski A., Boćkowski M., Grzegory I., Porowski S.
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EN
We present the results of electron paramagnetic resonance investigations of GaN bulk crystals doped with Mn. The EPR experiment shows the Mn^{2+} resonance in all the investigated n-type crystals, while in highly resistive samples extra doped with Mg acceptor the Mn^{2+} resonance decreases. This is a consequence of the location of Mn acceptor level in GaN band gap. The analysis of the spin relaxation times reveals the Korringa scattering as the dominating spin relaxation mechanism in n-type GaN:Mn crystals. The effective exchange constant determined from spin relaxation rate temperature dependence is of the order of 14 meV.
17
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Mechanisms of Yellow and Red Photoluminescence in Wurtzite and Cubic GaN

33%
Godlewski M., Suski T., Grzegory I., Porowski S., Langer R., Barski A., Bergman J., Monemar B., Goldys E., Phillips M.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
326-330
EN
The origin of two "deep" photoluminescence (PL) emissions observed in wurtzite (yellow PL) and cubic (red PL) GaN is discussed. PL and time-resolved PL studies confirm donor-acceptor pair character of the yellow band in wurtzite GaN and point to participation of shallow donors in this emission. A similar PL mechanism is proposed for the red emission of cubic GaN. We further show a puzzling property of both yellow and red PLs. Both yellow and red emissions show spatial homogeneity and are only weakly dependent on surface morphology.
18
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Cathodoluminescence Profiling of InGaN-Based Quantum Well Structures and Laser Diodes - In-Plane Instabilities of Light Emission

27%
Godlewski M., Ivanov V., Goldys E., Phillips M., Böttcher T., Figge S., Hommel D., Czernecki R., Prystawko P., Leszczynski M., Perlin P., Grzegory I., Porowski S.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
689-694
EN
Instabilities of light emission and also of stimulated emission in series of GaN epilayers and InGaN quantum well structures, including laser diode structures, are studied. A stimulated emission is observed under electron beam pumping. This enabled us to study light emission properties from laser structures and their relation to microstructure details. We demonstrate large in-plane fluctuations of light emission and that these fluctuations are also present for excitation densities larger than the threshold densities for the stimulated emission.
19
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High Power Continuous Wave Blue InAlGaN Laser Diodes Made by Plasma Assisted MBE

27%
Skierbiszewski C., Siekacz M., Wiśniewski P., Perlin P., Feduniewicz-Żmuda A., Cywiński G., Smalc J., Grzanka S., Grzegory I., Leszczyński M., Porowski S.
Acta Physica Polonica A
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2006
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vol. 110
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issue 3
345-351
EN
Room temperature, continuous wave operation of InGaN multi-quantum wells laser diodes made by rf plasma assisted molecular beam epitaxy at 411 nm wavelength is demonstrated. The threshold current density and voltage were 4.2 kA/cm^2 and 5.3 V, respectively. High optical power output of 60 mW was achieved. The lifetime of these laser diodes exceeds 5 h with 2 mW of optical output power. The laser diodes are fabricated on low dislocation density bulk GaN substrates, at growth conditions which resembles liquid phase epitaxy. We demonstrate that relatively low growth temperatures (600-700°C) pose no intrinsic limitations for fabrication of nitride optoelectronic components by plasma assisted molecular beam epitaxy.
20
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Crack Free GaInN/AlInN Multiple Quantum Wells Grown on GaN with Strong Intersubband Absorption at 1.55μm

27%
Cywiński G., Skierbiszewski C., Feduniewicz-Żmuda A., Siekacz M., Nevou L., Doyennette L., Julien F., Prystawko P., Kryśko M., Grzanka S., Grzegory I., Porowski S.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
175-181
EN
Crack free GaInN/AlInN multiple quantum wells were grown by rf plasma-assisted molecular beam epitaxy on (0001) GaN/sapphire substrates. The strain-engineering concept was applied to eliminate cracking effect for growth of intersubband structures on GaN. Indium contained ternary compounds of barrier and well layers are contrary strained to the substrate material. A series of crack free GaInN/AlInN intersubband structures on (0001) GaN was fabricated and investigated. The assumed composition and layered structure were confirmed by room temperature photoluminescence and X-ray diffraction measurements. The intersubband measurements were done in multipass waveguide geometry by applying direct intersubband absorption and photoinduced intersubband absorption measurements. The optimized structure design contains forty periods of Si-doped GaInN/AlInN quantum wells and exhibits strong intersubband absorption.
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