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1

Superconductivity Study of GaN Highly Doped by Transition Metals

100%

Gosk J., Boćkowski M., Tokarczyk M., Kowalski G., Twardowski A.

Acta Physica Polonica A

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2013

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vol. 124

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issue 5

877-880

EN

GaN:Cr and GaN:Fe single crystals as well as GaN:Mn micropowders highly doped by transition metals were grown to investigate low temperature superconductivity. Magnetic measurements revealed type I superconductivity with T_{C} ≈ 6 K and H_{C} ≈ 600 Oe, identical for all compounds and also identical to that observed before in GaP:Cr and GaAs:Cr. The presence of amorphous inclusions of gallium may explain existing superconductivity as a result of a phase transition leading to β-Ga during cooling down of the sample. Since the observed parameters are close to those characteristic for superconducting Ga(II) this possibility could not be ruled out.

2

Observation of Magnetic Anisotropy in GaN:Cr Single Crystals

86%

Gosk J., Boćkowski M., Kowalski G., Grzegory I., Szczytko J., Twardowski A.

Acta Physica Polonica A

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2012

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vol. 122

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issue 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.

3

Time-Resolved Studies of Gallium Nitride Doped with Gadolinium

86%

Witek B., Wysmołek A., Kamińska M., Twardowski A., Potemski M., Boćkowski M., Grzegory I.

Acta Physica Polonica A

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2008

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vol. 114

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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.

4

Photoluminescence Study of Bulk GaN Doped with Beryllium

86%

Jaworek M., Wysmołek A., Kamińska M., Twardowski A., Boćkowski M., Grzegory I.

Acta Physica Polonica A

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2005

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vol. 108

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issue 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.

5

Measurement of Very Small Zeeman Splittings in GaN:Mn,Mg by Faraday Rotation

73%

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.

6

Coupling of LO Phonons to Excitons in GaN

73%

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.

7

Photoluminescence and Electron Paramagnetic Resonance Studies of Bulk GaN Doped with Gadolinium

73%

Lipińska Z., Pawłowski M., Żołnierowicz H., Wysmołek A., Palczewska M., Kamińska M., Twardowski A., Boćkowski M., Grzegory I.

Acta Physica Polonica A

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2006

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vol. 110

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issue 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.

8

Mn Impurity in GaN Studied by Electron Paramagnetic Resonance

73%

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.

9

High Resistivity GaN Single Crystalline Substrates

59%

Porowski S., Boćkowski M., Łucznik B., Grzegory I., Wróblewski M., Teisseyre H., Leszczyński M., Litwin-Staszewska E., Suski T., Trautman P., Pakuła K., Baranowski J.

Acta Physica Polonica A

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1997

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vol. 92

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issue 5

958-962

EN

High resistivity 10^{4}-10^{6} Ω cm (300 K) GaN single crystals were obtained by solution growth under high N_{2} pressure from melted Ga with 0.1-0.5at.% of Mg. Properties of these crystals are compared with properties of conductive crystals grown by a similar method from pure Ga melt. In particular, it is shown that Mg-doped GaN crystals have better structural quality in terms of FWHM of X-ray rocking curve and low angle boundaries. Temperature dependence of electrical resistivity suggests hopping mechanism of conductivity. It is also shown that strain free GaN homoepitaxial layers can be grown on the Mg-doped GaN substrates.

10

Thermal Expansion of GaN Bulk Crystals and Homoepitaxial Layers

59%

Leszczyński M., Teisseyre H., Suski T., Grzegory I., Boćkowski M., Jun J., Pałosz B., Porowski S., Pakuła K., Baranowski J., Barski A.

Acta Physica Polonica A

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1996

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vol. 90

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issue 5

887-890

EN

Thermal expansion of gallium nitride was measured using high resolution X-ray diffraction. The following samples were examined: (i) single monocrystals grown at pressure of about 15 kbar, (ii) homoepitaxial layers. The main factor influencing both, the lattice parameters and the thermal expansion coefficient, are free electrons related to the nitrogen vacancies. The origin of an increase in the lattice constants by free electrons is discussed in terms of the deformation potential of the conduction-band minimum. An increase of the thermal expansion by free electrons is explained by a decrease of elastic constants.

11

Blue Laser on High N_2 Pressure-Grown Bulk GaN

46%

Grzegory I., Boćkowski M., Krukowski S., Łucznik B., Wróblewski M., Weyher J., Leszczyński M., Prystawko P., Czernecki R., Lehnert J., Nowak G., Perlin P., Teisseyre H., Purgał W., Krupczyński W., Suski T., Dmowski L., Litwin-Staszewska E., Skierbiszewski C., Łepkowski S., Porowski S.

Acta Physica Polonica A

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2001

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vol. 100

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issue Supplement

229-232

EN

In this note we report briefly on the details of pulsed-current operated "blue" laser diode, constructed in our laboratories, which utilizes bulk GaN substrate. As described in Ref. [1] the substrate GaN crystal was grown by HNPSG method, and the laser structure was deposited on the conducting substrate by MOCVD techniques (for the details see Sec. 2 and Sec. 4 of Ref.~[1], respectively).

Refine search results

Superconductivity Study of GaN Highly Doped by Transition Metals

Observation of Magnetic Anisotropy in GaN:Cr Single Crystals

Time-Resolved Studies of Gallium Nitride Doped with Gadolinium

Photoluminescence Study of Bulk GaN Doped with Beryllium

Measurement of Very Small Zeeman Splittings in GaN:Mn,Mg by Faraday Rotation

Coupling of LO Phonons to Excitons in GaN

Photoluminescence and Electron Paramagnetic Resonance Studies of Bulk GaN Doped with Gadolinium

Mn Impurity in GaN Studied by Electron Paramagnetic Resonance

High Resistivity GaN Single Crystalline Substrates

Thermal Expansion of GaN Bulk Crystals and Homoepitaxial Layers

Blue Laser on High N_2 Pressure-Grown Bulk GaN