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4 Acta Physica Polonica A

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Effect of Deep-Level Defects on Transient Photoconductivity of Semi-Insulating 4H-SiC

100%

Suproniuk M. , Kamiński P. , Kozłowski R. , Pawłowski M.

Acta Physica Polonica A

2014

tom 125

nr 4

1042-1048

A model enabling the equilibrium conductivity and transient photoconductivity of semi-insulating 4H-SiC to be simulated has been demonstrated. Using this model, the simulations of both equilibrium conductivity and transient photoconductivity have been carried out. Both the simulation and experimental results have shown that the evolution of photoconductivity in time after switching on the band-to-band generation of electron-hole pairs is strongly affected by the properties of deep level defects. The results of transient photocurrent measurements confirm the simulations results indicating that the Z_{1/2} center is a very effective recombination center in semi-insulating 4H-SiC having detrimental effect on the transient photoconductivity.

EPR Spectra of Multispin Systems. Application to Poly-m-p-Aniline

75%

Juszyński P. , Twardowski A. , Gosk J. , Kulszewicz-Bajer I. , Pawłowski M. , Dziatkowski K. , Szczytko J.

Acta Physica Polonica A

2011

tom 119

nr 5

717-719

In this communication we present NiceMagnetic, software for simulations and analysis of EPR spectrum and SQUID measurements. Systems of arbitrary number N of spin-only magnetic moments (S ≤ 0 and L = 0) were considered within the lines of the Heisenberg and Zeeman Hamiltonians. Effective algorithms used for the computations are discussed. This includes modified secant method adapted to calculate resonance fields with demanded precision. Finally, application of NiceMagnetic to experimental SQUID magnetization and EPR spectra of poly-m-p-aniline, one of recently synthesized high spin polymers containing unpaired electrons will be presented. As a result, exchange integral between electron and nitrogen nuclei spins (ligand hyperfine interaction) J = 6.3 × 10^{-4} cm^{-1} was estimated.

Mn Impurity in Bulk GaAs Crystals

63%

Pawłowski M. , Piersa M. , Wołoś A. , Palczewska M. , Strzelecka G. , Hruban A. , Gosk J. , Kamińska M. , Twardowski A.

Acta Physica Polonica A

2005

tom 108

nr 5

825-830

Magnetic and electron transport properties of GaAs:Mn crystals grown by Czochralski method were studied. Electron spin resonance showed the presence of Mn acceptor A in two charge states: singly ionized A^- in the form of Mn^{2+}(d^5), and neutral A^0 in the form of Mn^{2+}(d^5) plus a bound hole (h). It was possible to determine the relative concentration of both types of centers from intensity of the corresponding electron spin resonance lines. Magnetization measured as a function of magnetic field (up to 6 T) in the temperature range of 2-300 K revealed overall paramagnetic behavior of the samples. Effective spin was found to be about 1.5 value, which was consistent with the presence of two types of Mn configurations. In most of the studied samples the dominance of Mn^{2+}(d^5)+h configuration was established and it increased after annealing of native donors. The total value of Mn content was obtained from fitting of magnetization curves with the use of parameters obtained from electron spin resonance. In electron transport, two mechanisms of conductivity were observed: valence band transport dominated above 70 K, and hopping conductivity within Mn impurity band at lower temperatures. From the analysis of the hopping conductivity and using the obtained values of the total Mn content, the effective radius of Mn acceptor in GaAs was estimated as a = 11±3Å.

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

63%

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

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.