Işık, Mehmet

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https://hdl.handle.net/20.500.14411/8160
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Mehmet, Işık
M.,Işık
Isik, Mehmet
Mehmet, Isik
I., Mehmet
I.,Mehmet
Işık,M.
Isik,M.
I.,Mehmet
M.,Isik
Işık, Mehmet
M., Isik
Isik, M.
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Profesör Doktor
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mehmet.isik@atilim.edu.tr
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Department of Electrical & Electronics Engineering
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Former Staff
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Scholarly Output

173

Articles

169

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Optical Materials17
Physica B: Condensed Matter16
Journal of Luminescence15
Materials Science in Semiconductor Processing14
Journal of Materials Science: Materials in Electronics12
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Subject: Semiconductors

Scholarly Output Search Results

Now showing 1 - 10 of 38
  • Thumbnail Image
    Article
    Citation - WoS: 7
    Citation - Scopus: 7
    Interband Critical Points in Tlgax< Layered Mixed Crystals (0 ≤ x ≤ 1)
    (Elsevier Science Sa, 2013) Isik, M.; Işık, Mehmet; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics Engineering
    The layered semiconducting TlGaxIn1-xS2 mixed crystals (0 <= x <= 1) were studied by spectroscopic ellipsometry measurements in the 1.2-6.2 eV spectral range at room temperature. The spectral dependence of the components of the complex dielectric function, refractive index and extinction coefficient were revealed using an optical model. The interband transition energies in the studied samples were found from the analysis of the second-energy derivative spectra of the complex dielectric function. The variation of the obtained energies with composition were plotted to see the effect of the substitution of indium with gallium. Moreover, a simple diagram showing the revealed transitions in the available electronic band structure was given for TlGaS2 single crystals. (C) 2013 Elsevier B.V. All rights
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    Article
    Citation - WoS: 2
    Determination of Optical Constants and Temperature Dependent Band Gap Energy of Gas0.25se0.75< Single Crystals
    (Natl inst Optoelectronics, 2017) Isik, M.; Gasanly, N.
    Optical properties of GaS0.25Se0.75 single crystals were investigated by means of temperature -dependent transmission and room temperature reflection experiments. Derivative spectrophotometry analysis showed that indirect band gap energies of the crystal increase from 2.13 to 2.26 eV as temperature is decreased from 300 to 10 K. Temperature dependence of band gap energy was fitted under the light of theoretical expression. The band gap energy change with temperature and absolute zero value of the band gap energy were found from the analyses. The Wemple-DiDomenico single effective oscillator model and Sellmeier oscillator model were applied to the spectral dependence of room temperature refractive index to find optical parameters of the GaS0.25Se0.75 crystal. Chemical composition of the crystal was determined using the energy dispersive spectral measurements.
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    Article
    Citation - WoS: 8
    Citation - Scopus: 8
    Study of Vibrational Modes in (ga2s3< - (ga2se3< Mixed Crystals by Raman and Infrared Reflection Measurements
    (Elsevier, 2019) Isik, M.; Guler, I.; Gasanly, N. M.
    Raman and infrared (IR) reflection characteristics were investigated in the frequency region of 100-450 cm(-1) for (Ga2S3)(x) - (Ga2Se3)(1-x) mixed crystals for compositions of x increasing from 0.0 to 1.0 by intervals of 0.25 obtained by Bridgman crystal growth technique. In the Raman spectra of these crystals four dominant peak features were observed while two bands were detected in the IR spectra of interest samples. Kramers-Kronig dispersion relations applied to IR spectra presented the frequencies of transverse optical modes. The compositional dependencies of revealed Raman- and IR-active mode frequencies on (Ga2S3)(x) - (Ga2Se3)(1-x) crystals were established. One-mode behavior was displayed from indicated dependencies.
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    Article
    Citation - WoS: 3
    Citation - Scopus: 4
    Optical Properties of Cu3in5< Single Crystals by Spectroscopic Ellipsometry
    (Elsevier Gmbh, 2018) Isik, M.; Nasser, H.; Ahmedova, F.; Guseinov, A.; Gasanly, N. M.
    Cu3In5S9 single crystals were investigated by structural methods of x-ray diffraction and energy dispersive spectroscopy and optical techniques of ellipsometry and reflection carried out at room temperature. The spectral dependencies of optical constants; dielectric function, refractive index and extinction coefficient, were plotted in the range of 1.2-6.2 eV from ellipsometric data. The spectra of optical constants obtained from ellipsometry analyses and reflectance spectra presented a sharp change around 1.55 and 1.50 eV, respectively, which are associated with band gap energy of the crystal. The critical point (interband transition) energies were also found from the analyses of second-energy derivative of real and imaginary components of dielectric function. The analyses indicated the presence of four critical points at 2.73, 135, 4.04 and 4.98 eV.
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    Article
    Citation - WoS: 5
    Citation - Scopus: 7
    Temperature-Dependent Electrical Resistivity, Space-Charge Current and Photoconductivity of Ga0.75in0.25< Single Crystals
    (Elsevier Science Bv, 2013) Isik, M.; Gasanly, N. M.
    Dark electrical resistivity, space-charge-limited (SCL) current and photoconductivity measurements were carried out on Ga0.75In0.25Se single crystals. Analysis of the dark resistivity measurements revealed the presence of one level with activation energy of 0.10 eV. Current voltage characteristics showed that both ohmic and SCL characters exhibit in 180-300 K range. Analysis of the experimental data in the SCL region resulted with a trap level at 0.11 eV above the valence band. Photoconductivity measurements were performed at different light intensities in the temperature range of 150-300 K. Behavior of the recombination mechanism in the crystal was brought out as sublinear recombination from the dependence of photocurrent on illumination intensity. Moreover, obtained activation energies were compared with the results of other experimental techniques applied to Ga0.75In0.25Se crystals in literature. (C) 2013 Elsevier B.V. All rights reserved.
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    Article
    Citation - Scopus: 3
    Determination of optical constants and temperature dependent band gap energy of GaS0.25Se0.75 single crystals
    (National Institute of Optoelectronics, 2017) Isik,M.; Gasanly,N.
    Optical properties of GaS0.25Se0.75 single crystals were investigated by means of temperature-dependent transmission and room temperature reflection experiments. Derivative spectrophotometry analysis showed that indirect band gap energies of the crystal increase from 2.13 to 2.26 eV as temperature is decreased from 300 to 10 K. Temperature dependence of band gap energy was fitted under the light of theoretical expression. The band gap energy change with temperature and absolute zero value of the band gap energy were found from the analyses. The Wemple-DiDomenico single effective oscillator model and Sellmeier oscillator model were applied to the spectral dependence of room temperature refractive index to find optical parameters of the GaS0.25Se0.75 crystal. Chemical composition of the crystal was determined using the energy dispersive spectral measurements.
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    Article
    Low Temperature Thermoluminescence of Quaternary Thallium Sulfide Tl4inga3<
    (indian Assoc Cultivation Science, 2015) Delice, S.; Isik, M.; Bulur, E.; Gasanly, N. M.
    Thermoluminescence measurements have been carried out on Tl4InGa3S8 single crystals in the temperature range of 10-300 K at various heating rates. The observed thermoluminescence spectra have been analyzed applying many methods like curve fitting, initial rise, peak shape and heating rate methods. Thermal cleaning method has been performed on the observed thermoluminescence glow curve to separate the overlapped peaks. Three distinctive trapping centers with activation energies of 13, 44 and 208 meV have been revealed from the results of the analysis. Heating rate dependence and traps distribution investigations have been also undertaken on the most intensive peak. The thermoluminescence mechanisms in the observed traps have been attributed to first order kinetics (slow retrapping) on the strength of the consistency between theoretical assumptions for slow retrapping process and experimental outcomes.
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    Article
    Citation - WoS: 24
    Citation - Scopus: 22
    Spectroscopic Ellipsometry Study of Above-Band Gap Optical Constants of Layered Structured Tlgase2, Tlgas2 and Tlins2 Single Crystals
    (Elsevier Science Bv, 2012) Isik, M.; Gasanly, N. M.; Turan, R.
    Spectroscopic ellipsometry measurements on TlGaSe2, TlGaS2 and TlInS2 layered crystals were carried out on the layer-plane (0 0 1) surfaces, which are perpendicular to the optic axis c*, in the 1.2- 6.2 eV spectral range at room temperature. The real and imaginary parts of the pseudodielectric function as well as pseudorefractive index and pseudoextinction coefficient were found as a result of analysis of ellipsometric data. The structures of critical points in the above-band gap energy range have been characterized from the second derivative spectra of the pseudodielectric function. The analysis revealed four, five and three interband transition structures with critical point energies 2.75, 3.13, 3.72 and 4.45 eV (TlGaSe2), 3.03, 3.24, 3.53, 4.20 and 4.83eV (TlGaS2), and 3.50, 3.85 and 4.50 eV (TlInS2). For TlGaSe2 crystals, the determined critical point energies were assigned tentatively to interband transitions using the available electronic energy band structure. (c) 2012 Elsevier B.V. All rights reserved.
  • Thumbnail Image
    Article
    Citation - WoS: 14
    Citation - Scopus: 15
    Structural and Optical Properties of Ga2se3< Crystals by Spectroscopic Ellipsometry
    (Springer, 2019) Guler, I.; Isik, M.; Gasanly, N. M.; Gasanova, L. G.; Babayeva, R. F.
    Optical and crystalline structure properties of Ga2Se3 crystals were analyzed utilizing ellipsometry and x-ray diffraction (XRD) experiments, respectively. Components of the complex dielectric function (epsilon=epsilon(1)+i epsilon(2)) and refractive index (N=n+ik) of Ga2Se3 crystals were spectrally plotted from ellipsometric measurements conducted from 1.2eV to 6.2eV at 300K. From the analyses of second-energy derivatives of epsilon(1) and epsilon(2), interband transition energies (critical points) were determined. Absorption coefficient-photon energy dependency allowed us to achieve a band gap energy of 2.02eV. Wemple and DiDomenico single effective oscillator and Spitzer-Fan models were accomplished and various optical parameters of the crystal were reported in the present work.
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    Article
    Citation - WoS: 7
    Citation - Scopus: 7
    Trapping Centers and Their Distribution in Tl2ga2< Layered Single Crystals
    (Pergamon-elsevier Science Ltd, 2009) Isik, M.; Gasanly, N. M.
    Thermally stimulated current (TSC) measurements with current flowing perpendicular to the layers were carried out on Tl2Ga2Se3S layered single crystals in the temperature range of 10-260K. The experimental data were analyzed by using different methods, such as curve fitting, initial rise and isothermal decay methods. The analysis revealed that there were three trapping centers with activation energies of 12, 76 and 177 meV. It was concluded that retrapping in these centers was negligible, which was confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. The capture cross section and the concentration of the traps have been also determined. An exponential distribution of electron traps was revealed from the analysis of the TSC data obtained at different light illumination temperatures. This experimental technique provided values of 10 and 88 meV/decade for the traps distribution related to two different trapping centers. (C) 2009 Elsevier Ltd. All rights reserved.