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4 Acta Physica Polonica A

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Observation of Magnetic Anisotropy in GaN:Cr Single Crystals

100%

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

nr 6

1007-1009

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.

Time-Resolved Studies of Gallium Nitride Doped with Gadolinium

100%

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

nr 5

1425-1430

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.

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

84%

Wołoś A. , Kossacki P. , Golnik A. , Kamińska M. , Gaj J. , Twardowski A. , Grzegory I. , Boćkowski M. , Porowski S.

nr 4-5

695-699

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.

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

84%

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

tom 110

nr 2

243-248

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.

High Resistivity GaN Single Crystalline Substrates

67%

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.

nr 5

958-962

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.