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1
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Temperature Dependence of the First-Order Raman Phonon Lines in GaS_{0.25}Se_{0.75} Layered Crystals

100%
Gasanly N.
Acta Physica Polonica A
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2002
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vol. 102
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issue 6
801-810
EN
Systematic measurements by Raman scattering of the frequency and line width of the zone-center optical modes in GaS_{0.25}Se_{0.75} layered crystal over the temperature range of 10-300 K are carried out. The analysis of temperature dependence of intralayer modes shows that frequency shift and line broadening are successfully modeled by including the contributions from thermal expansion and lattice anharmonicity. The purely anharmonic contribution (phonon-phonon coupling) is found to be due to three-phonon processes.
2
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Tuning Optical Absorption Edge by Composition and Temperature in TlGaS_{2x}Se_{2(1-x)} Layered Mixed Crystals (0 ≤ x ≤ 1)

100%
Gasanly N.
Acta Physica Polonica A
|
2012
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vol. 122
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issue 4
728-731
EN
Optical properties of TlGaS_{2x}Se_{2(1-x)} mixed crystals (0 ≤ x ≤1) have been studied using the transmission and reflection measurements in the wavelength range of 400-1100 nm. The optical indirect band gap energies were determined through the analysis of the absorption data. It was found that the energy band gaps increase with increase of sulfur atoms content in TlGaS_{2x}Se_{2(1-x)} mixed crystals. From the transmission measurements carried out in the temperature range of 10-300 K, the rates of change of the indirect band gaps with temperature were established for the different compositions of mixed crystals studied.
3
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Radiative Donor-Acceptor Pair Recombination in Tl_2Ga_2Se_3S Layered Single Crystals

100%
Gasanly N.
Acta Physica Polonica A
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2013
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vol. 124
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issue 1
128-132
EN
The emission band spectra of Tl_2Ga_2Se_3S layered crystals have been studied in the temperature range of 10-50 K and in the wavelength region of 540-700 nm. A broad photoluminescence band centered at 626 nm (1.98 eV) was observed at T=10 K. Variation of emission band has been studied as a function of excitation laser intensity in the 0.4-51.5 mW cm^{-2} range. The analysis of the spectra reveals that the peak energy position changes with laser excitation intensity (blue shift). This behavior of the emission band is in agreement with the idea of separation inhomogeneity of donor-acceptor pairs. Radiative transitions from the moderately deep donor level E_{d}=270 meV to the shallow acceptor level E_{a}=10 meV were suggested to be responsible for the observed photoluminescence band.
4
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Influence of Isomorphic Atom Substitution on Lattice Anisotropy of Thallium Dichalcogenide Layered Mixed Crystals

100%
Gasanly N.
|
EN
Compositional variation of the lattice parameters of TlBX_2-type (B = Ga or In and X = S or Se) mixed crystals with monoclinic structure were studied by X-ray diffraction technique. The lattice anisotropy (c/b) of these mixed crystals changes linearly with substitution of the atoms located both at the centers and the vertices of the corresponding BX_4 tetrahedra. A brief survey of the important features of the effect of isomorphic atom substitution on the lattice anisotropy and the unit cell volume of TlBX_2-type mixed crystals with layered structure was presented.
5
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Thermally Stimulated Current Study of Shallow Traps in As-Grown TlInSe_2 Chain Crystals

64%
Gasanly N., Yildirim T.
Acta Physica Polonica A
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2011
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vol. 119
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issue 3
437-441
EN
Thermally stimulated current measurements were carried out on as-grown TlInSe_2 single crystals. The investigations were performed in temperatures ranging from 10 to 260 K with heating rate of 0.3 K s^{-1}. The analysis of the data revealed the hole traps levels located at 6 and 57 meV. The activation energies of the traps have been determined using various methods of analysis, and they agree with each other. The concentration (2.8 × 10^{13} and 3.4 × 10^{12} cm^{-3}) and capture cross section (4.1 × 10^{-28} and 2.9 × 10^{-26} cm^2) of the traps were estimated for peaks A and B, respectively. It was concluded that in these centers retrapping was negligible, as confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping.
6
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Low-Temperature Raman Scattering in TlGa_xIn_{1-x}S_2 Layered Mixed Crystals: Compositional Dependence of the Mode Frequencies and Line Shapes

64%
Gasanly N., Yuksek N.
Acta Physica Polonica A
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2005
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vol. 108
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issue 6
997-1003
EN
The Raman spectra of TlGa_xIn_{1-x}S_2 layered mixed crystals were studied for a wide range of composition (0≤x≤1) at T=50 K. The effect of crystal disorder on the line width broadening of the Raman-active modes are discussed. The asymmetry in the Raman line shape is analyzed for two interlayer and intralayer modes exhibiting one-mode behavior.
7
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Compositional Dependence of Optical Modes Frequencies in TlGa_xIn_{1-x}S_2 Layered Mixed Crystals (0 ≤ x ≤1)

51%
Isik M., Gasanly N., Korkmaz F.
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vol. 126
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issue 3
747-751
EN
The infrared transmittance and Raman scattering spectra in TlGa_xIn_{1-x}S_2 (0 ≤ x ≤1) layered mixed crystals grown by the Bridgman method were studied in the frequency ranges of 400-2000 and 250-400 cm^{-1}, respectively. The bands observed at room temperature in IR transmittance spectra of TlGa_xIn_{1-x}S_2 were interpreted in terms of multiphonon absorption processes. The dependences of the frequencies of IR- and Raman-active modes on the composition of TlGa_xIn_{1-x}S_2 mixed crystals were also established. The structural characterization of the mixed crystals was investigated by means of X-ray diffraction measurements and compositional dependence of lattice parameters was revealed.
8
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Optical Absorption and Reflection Studies of Tl_4InGa_3S_8 Layered Single Crystals

51%
Goksen K., Gasanly N., Ozkan H.
Acta Physica Polonica A
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2007
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vol. 112
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issue 1
93-100
EN
The optical properties of Tl_4InGa_3S_8 layered single crystals have been studied by means of transmission and reflection measurements in the wavelength region between 400 and 1100 nm. The analysis of the room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 2.40 and 2.61 eV, respectively. Transmission measurements carried out in the temperature range of 10-300 K revealed the rate of change of the indirect band gap with temperature asγ=-6.0×10^{-4} eV/K. The absolute zero value of the band gap energy was obtained as E_{gi}(0)= 2.52 eV. The dispersion of the refractive index is discussed in terms of the Wemple-DiDomenico single-effective-oscillator model. The refractive index dispersion parameters: oscillator energy, dispersion energy, oscillator strength, and zero-frequency refractive index were found to be 5.07 eV, 26.67 eV, 8.82×10^{13} m^{-2}, and 2.50, respectively.
9
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Photovoltaic Effect and Space Charge Limited Current Analysis in TlGaTe_2 Crystals

51%
Qasrawi A., Yaseen T., Eghbariy B., Gasanly N.
Acta Physica Polonica A
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2012
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vol. 122
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issue 1
152-155
EN
Anisotropic space charge limited current density analysis and photovoltaic effect in TlGaTe_2 single crystals has been investigated. It is shown that, above 330 K, the crystal exhibits intrinsic and extrinsic type of conductivity along (c-axis) and perpendicular (a-axis) to the crystal's axis, respectively. The current density (J) is found to be space charge limited. It is proportional to the square and three halves power of voltage (V) along the a- and c-axis, respectively. Along the a-axis and at sufficiently low electric field values, the activation energy of the current density is found to depend on the one half power of electric field. At high electric fields, the activation energy is field invariant. This behavior is found to be due to the Pool-Frenkel effect and due to a trap set located at 0.26 eV, respectively. Along the c-axis the crystal is observed to operate under the Child-Langmuir space charge limited regime. TlGaTe_2 crystals are found to exhibit photovoltaic properties. The open circuit photovoltage is recorded as a function of illumination intensity at room temperature.
10
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Excitation and Temperature Tuned Photoluminescence in Tl_2In_2S_3Se Layered Crystals

51%
Guler I., Goksen K., Gasanly N.
Acta Physica Polonica A
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2006
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vol. 110
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issue 6
823-831
EN
Photoluminescence spectra of Tl_2In_2S_3Se layered single crystals have been studied in the wavelength region of 535-725 nm and in the temperature range of 22-58 K. Two photoluminescence bands centered at 564 (2.20 eV, A-band) and 642 nm (1.93 eV, B-band) were observed at T = 22 K. Variations of both bands have been investigated as a function of excitation laser intensity in the range from 16 to 516 mW cm^{-2}. These bands are attributed to recombination of charge carriers through donor-acceptor pairs located in the band gap. Radiative transitions from shallow donor levels located 0.02 and 0.01 eV below the bottom of conduction band to acceptor levels located 0.05 and 0.44 eV above the top of the valence band are suggested to be responsible for the observed A- and B-bands in the photoluminescence spectra, respectively.
11
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Trapping Center Parameters in N-Implanted Tl_2Ga_2S_3Se Single Crystals by Thermally Stimulated Currents Measurements

51%
Yildirim T., Gasanly N., Turan R.
Acta Physica Polonica A
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2013
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vol. 123
|
issue 4
766-769
EN
As-grown Tl_2Ga_2S_3Se crystals have been doped by ion implantation technique. The samples were bombarded at room temperature in the direction perpendicular to the layer by N ion beam of about 120 keV having dose of 1 × 10^{16} ions/cm^2. The effect of N implantation with annealing at 300C was studied by using thermally stimulated current measurements. The investigations were performed in temperatures ranging from 10 to 290 K. The experimental evidence was found for presence of one deep hole trapping center with activation energy of 392 meV. The capture cross-section was calculated as 3.9 × 10^{-20} cm^2. Also the concentration of the traps was estimated to be 8.0 × 10^{11} cm^{-3}.
12
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Trapping Center Parameters in TlInS_2 Layered Crystals by Thermally Stimulated Current Measurements

51%
Yuksek N., Gasanly N., Ozkan H., Karci O.
Acta Physica Polonica A
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2004
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vol. 106
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issue 1
95-103
EN
Thermally stimulated current measure ments are carried out on TlInS_2 layered single crystal with the current flowing perpendicular to the c-axis in the temperature range of 10 to 90 K. The results are analyzed according to various methods, such as curve fitting, heating rate, and initial rise methods, which seem to be in good agreement with each other. Experimental evidence is found for one trapping center in TlInS_2 crystal in the low-temperature region.
13
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Analysis of Thermoluminescence Glow Peaks in β-Irradiated TlGaSeS Crystals

51%
Isik M., Yildirim T., Gasanly N.
Acta Physica Polonica A
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2016
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vol. 129
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issue 6
1165-1168
EN
Thermoluminescence properties of TlGaSeS layered single crystals were investigated in the temperature range of 280-720 K. Thermoluminescence glow curve exhibited three peaks with maximum temperatures of ≈370, 437, and 490 K. Curve fitting, initial rise and peak shape methods were used to determine the activation energies of the trapping centers. All applied methods resulted with energies around 0.82, 0.91, and 0.99 eV. Dose dependence of the thermoluminescence intensity was also examined for the doses in the range of 0.7-457.6 Gy. Peak maximum intensity of the observed peak around 370 K showed an increase up to a certain dose and then a decrease at higher doses. This non-monotonic dose dependence was discussed under the light of a reported model in which different kinds of competition between radiative and nonradiative recombination centers during excitation or heating stages of the thermoluminescence process are explained.
14
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Low-Temperature Thermoluminescence Studies on TlInS_{2} Layered Single Crystals

51%
Isik M., Delice S., Gasanly N.
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vol. 126
|
issue 6
1299-1303
EN
Thermoluminescence characteristics of TlInS_{2} layered single crystals grown by the Bridgman method were investigated in the low temperature range of 10-300 K. The illuminated sample with blue light ( ≈ 470 nm) at 10 K was heated at constant heating rate. Curve fitting, initial rise and various heating rate methods were used to determine the activation energy of the trap levels. All applied methods showed good consistency about the presence of five trapping centers located at 14, 19, 350, 420, and 520 meV. Behavior of the TL curve for various heating rates was investigated. Traps distribution has also been studied. The activation energies of the distributed trapping centers were found to be increasing from 14 to 46 meV.
15
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Deep Traps Distribution in TlInS_2 Layered Crystals

51%
Isik M., Gasanly N., Ozkan H.
Acta Physica Polonica A
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2009
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vol. 115
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issue 3
732-737
EN
The trap centers and distributions in TlInS_2 were studied in the temperature range of 100-300 K by using thermally stimulated currents technique. Experimental evidence was found for the presence of three trapping centers with activation energies 400, 570, and 650 meV. Their capture cross-sections were determined as 6.3 × 10^{-16}, 2.7× 10^{-12}, and 1.8× 10^{-11} cm^{2}, respectively. It was concluded that in these centers retrapping is negligible as confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. An exponential distribution of hole traps was revealed from the analysis of the thermally stimulated current data obtained at different light excitation temperatures. This experimental technique provided a value of 800 meV/decade for the trap distribution.
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