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  1. 30 Acta Physica Polonica A
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  1. 1 2016
  2. 1 2012
  3. 1 2008
  4. 3 2007
  5. 3 2006
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  1. 31 Grzegory I.
  2. 20 Porowski S.
  3. 10 Perlin P.
  4. 10 Suski T.
  5. 9 Boćkowski M.
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1
Content available remote Application of GaN Pressure Grown Crystals for Epitaxy of GaN-Based Structures
100%
Grzegory I.
Acta Physica Polonica A
|
2000
|
tom 98
|
nr 3
183-193
EN
The results obtained with the use of the pressure grown GaN single crystalline substrates allow to draw the following conclusions important for the construction of In-free UV light emitting diodes and lasers and InGaN-based high power blue lasers: 1. The application of the pressure grown GaN single crystalline substrates allows to grow near dislocation free layer structures by both metal organic chemical vapor deposition and MBE. 2. The elimination of dislocations leads to highly efficient UV emission from GaN and GaN/AlGaN quantum wells which is impossible for strongly dislocated structures grown on sapphire. 3. At high excitations (i.e. in lasers) dislocations are effective nonradiative recombination centers also in the InGaN containing structures, therefore the elimination of these defects is crucial for better performance of blue lasers. 4. The analysis of microstructural and optical properties of the InGaN containing dislocation free structures shows that the main mechanisms of carrier localization in InGaN are not related with the nm scale compositional fluctuations in InGaN. In the paper, the optical and structural properties of the near dislocation free GaN-based structures leading to the above conclusions are discussed.
2
Content available remote High Pressure Freeze-out of Electrons in Undoped GaN Crystal. Proof of Existence of Resonant Donor State (Nitrogen Vacancy)
38%
Perlin P. , Teisseyre H. , Suski T. , Leszczyński M. , Grzegory I. , Jun J. , Porowski S.
Acta Physica Polonica A
|
1995
|
tom 87
|
nr 1
141-143
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.
3
Content available Observation of Magnetic Anisotropy in Bulk GaMnN:Mg Crystals
38%
Gosk J. , Zając M. , Kamińska M. , Twardowski A. , Grzegory I. , Boć M. , Porowski S.
Acta Physica Polonica A
|
2003
|
tom 103
|
nr 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.
4
Content available remote Two-Electron Transition in Homoepitaxial GaN Layers
38%
Fiorek A. , Baranowski J. , Wysmołek A. , Pakuła K. , Wojdak M. , Grzegory I. , Porowski S.
Acta Physica Polonica A
|
1997
|
tom 92
|
nr 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.
5
Content available remote Deep-Level Defects in MBE-Grown GaN-Based Laser Structure
38%
Tsarova T. , Wosiński T. , Mąkosa A. , Skierbiszewski C. , Grzegory I. , Perlin P.
Acta Physica Polonica A
|
2007
|
tom 112
|
nr 2
331-337
EN
We present results of deep-level transient spectroscopy investigations of defects in a GaN-based heterostructure of a blue-violet laser diode, grown by plasma-assisted molecular beam epitaxy on a bulk GaN substrate. Three majority-carrier traps, T1 at E_C - 0.28 eV, T2 at E_C - 0.60 eV, and T3 at E_V + 0.33 eV, were revealed in deep-level transient spectra measured under reverse-bias conditions. On the other hand, deep-level transient spectroscopy measurements performed under injection conditions, revealed one minority-carrier trap, T4, with the activation energy of 0.20 eV. The three majority-carrier traps were revealed in the spectra measured under different reverse-bias conditions, suggesting that they are present in various parts of the laser-diode heterostructure. In addition, these traps represent different charge-carrier capture behaviours. The T1 trap, which exhibits logarithmic capture kinetics, is tentatively attributed to electron states of dislocations in the n-type wave-guiding layer of the structure. In contrast, the T2, T3, and T4 traps display exponential capture kinetics and are assigned to point defects.
6
Content available remote Time-Resolved Studies of Gallium Nitride Doped with Gadolinium
38%
Witek B. , Wysmołek A. , Kamińska M. , Twardowski A. , Potemski M. , Boćkowski M. , Grzegory I.
Acta Physica Polonica A
|
2008
|
tom 114
|
nr 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.
7
Content available remote Observation of Magnetic Anisotropy in GaN:Cr Single Crystals
38%
Gosk J. , Boćkowski M. , Kowalski G. , Grzegory I. , Szczytko J. , Twardowski A.
|
|
nr 6
1007-1009
EN
Magnetic properties of bulk wurtzite GaN:Cr single crystals were studied with the magnetic field applied parallel and perpendicular to the crystal wurtzite c-axis. Structure of the crystal was examined by the X-ray diffraction method. Strong anisotropy of magnetization at low temperatures (2-10 K) was observed. The experimental data suggest Cr to be in nonspherical d^4 configuration.
8
Content available remote Luminescence Dynamics of Exciton Replicas in Homoepitaxial GaN Layers
38%
Korona K. , Baranowski J. , Pakuła K. , Monemar B. , Bergman J. , Grzegory I. , Porowski S.
Acta Physica Polonica A
|
1997
|
tom 92
|
nr 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.
9
Content available remote Crystallographic Properties of Bulk GaN Crystals Grown at High Pressure
38%
Leszczyński M. , Grzegory I. , Bockowski M. , Jun J. , Porowski S. , Jasiński J. , Baranowski J. M.
Acta Physica Polonica A
|
1995
|
tom 88
|
nr 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.
10
Content available remote Band Structure and Refractive Index of Gallium Nitride Under Pressure
38%
Perlin P. , Gorczyca I. , Suski T. , Teisseyre H. , Grzegory I. , Christensen N.
Acta Physica Polonica A
|
1991
|
tom 80
|
nr 3
421-424
EN
The effect of hydrostatic pressure on direct gap and refractive index of GaN is investigated up to 5.5 GPa. Band structure of GaN is calculated by Linear Muffin-Tin Orbitals (LMTO) method for different values of pressure. Resulting pressure coefficient of the main gap and of the refractive index are in a good agreement with the experimental ones.
11
Content available Photoluminescence Study of Bulk GaN Doped with Beryllium
38%
Jaworek M. , Wysmołek A. , Kamińska M. , Twardowski A. , Boćkowski M. , Grzegory I.
Acta Physica Polonica A
|
2005
|
tom 108
|
nr 4
705-710
EN
Photoluminescence of bulk GaN:Be grown by high pressure method is presented. The investigated crystals show well-resolved photoluminescence due to free and bound excitons similar to that observed for homoeptitaxial GaN layers. In addition to the excitonic transitions, pronounced luminescence band at 3.38 eV, due to Be acceptor, is observed. It was found that temperature behavior of this emission is typical of donor- and conduction band-acceptor transitions. The optical activation energy of Be acceptor is obtained to be of 60±15 meV.
12
Content available Measurement of Very Small Zeeman Splittings in GaN:Mn,Mg by Faraday Rotation
32%
Wołoś A. , Kossacki P. , Golnik A. , Kamińska M. , Gaj J. , Twardowski A. , Grzegory I. , Boćkowski M. , Porowski S.
Acta Physica Polonica A
|
2002
|
tom 102
|
nr 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.
13
Content available Mn Impurity in GaN Studied by Electron Paramagnetic Resonance
32%
Wołoś A. , Palczewska M. , Wilamowski Z. , Kamińska M. , Twardowski A. , Boćkowski M. , Grzegory I. , Porowski S.
Acta Physica Polonica A
|
2003
|
tom 103
|
nr 6
595-600
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.
14
Content available remote Mechanisms of Yellow and Red Photoluminescence in Wurtzite and Cubic GaN
32%
Godlewski M. , Suski T. , Grzegory I. , Porowski S. , Langer R. , Barski A. , Bergman J. , Monemar B. , Goldys E. , Phillips M.
Acta Physica Polonica A
|
1998
|
tom 94
|
nr 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.
15
Content available remote Magnetoluminescence Studies of GaN:Fe
32%
Niedźwiadek A. , Wysmołek A. , Wasik D. , Potemski M. , Szczytko J. , Kamińska M. , Twardowski A. , Łucznik B. , Pastuszka B. , Grzegory I.
Acta Physica Polonica A
|
2007
|
tom 112
|
nr 2
177-182
EN
We report on magneto-optical studies on iron doped GaN crystals grown using hydride vapor phase epitaxy method on bulk GaN substrate. The investigated samples showed an intensive 1.3 eV luminescence band, characteristic of Fe^{3+}(d^5) center in GaN. A high quality of the investigated samples allowed us to observe a well-resolved fine structure of intracenter transitions between ^4T_1(G) and ^6A_1(S) states, consisting of four sharp no-phonon lines. All the observed no-phonon lines showed pronounced splittings in magnetic field. From the analysis of the magneto-optical data, the structure of split ^4T_1(G) multiplet in the magnetic field applied along c-axis of GaN crystals was established.
16
Content available Photoluminescence and Electron Paramagnetic Resonance Studies of Bulk GaN Doped with Gadolinium
32%
Lipińska Z. , Pawłowski M. , Żołnierowicz H. , Wysmołek A. , Palczewska M. , Kamińska M. , Twardowski A. , Boćkowski M. , Grzegory I.
Acta Physica Polonica A
|
2006
|
tom 110
|
nr 2
243-248
EN
Photoluminescence and electron paramagnetic resonance experiments on strain free GaN bulk crystals of wurtzite structure doped with gadolinium are reported. Efficient gettering of residual GaN donors by Gd was observed. Electron paramagnetic resonance showed that Gd ion incorporated into GaN lattice had Gd^{3+}(4f^7) configuration. The observed photoluminescence spectra were explained as due to intracenter Gd^{3+}(4f^7) transitions. No ferromagnetic behavior was detected.
17
Content available remote III-V Semiconducting Nitrides Energy Gap under Pressure
32%
Perlin P. , Gorczyca I. , Teisseyre H. , Suski T. , Litwin-Staszewska E. , Porowski S. , Grzegory I. , Christensen N.
Acta Physica Polonica A
|
1992
|
tom 82
|
nr 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.
18
Content available remote Growth of GaN Metalorganic Chemical Vapour Deposition Layers on GaN Single Crystals
32%
Pakula K. , Baranowski J. M. , Stępniewski R. , Wysmołek A. , Grzegory I. , Jun J. , Porowski S. , Sawicki M. , Starowieyski K.
Acta Physica Polonica A
|
1995
|
tom 88
|
nr 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.
19
Content available remote Coupling of LO Phonons to Excitons in GaN
32%
Wysmołek A. , Łomiak P. , Baranowski J. , Pakuła K. , Stępniewski R. , Korona K. , Grzegory I. , Boćkowski M. , Porowski S.
Acta Physica Polonica A
|
1996
|
tom 90
|
nr 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.
20
Content available MnAs Overlayer on GaN(000_1)-(1 x 1) - Its Growth, Morphology and Electronic Structure
32%
Kowalski B. , Kowalik I. , Iwanowski R. , Łusakowska E. , Sawicki M. , Sadowski J. , Grzegory I. , Porowski S.
Acta Physica Polonica A
|
2004
|
tom 105
|
nr 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.
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