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Citation - WoS: 7
Citation - Scopus: 7
Trapping Centers and Their Distribution in Tl₂ga_{2< 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.
Hopping Conduction in Ga₄se_{3< Layered Single Crystals}
(Pergamon-elsevier Science Ltd, 2008) Qasrawi, A. F.; Gasanly, N. M.
The conduction mechanism in Ga4Se3S single crystals has been investigated by means of dark and illuminated conductivity measurements for the first time. The temperature-dependent electrical conductivity analysis in the region of 100-350 K, revealed the dominance of the thermionic emission and the thermally assisted variable range hopping (VRH) of charged carriers above and below 170 K, respectively. The density of states near the Fermi level and the average hopping distance for this crystal in the dark were found to be 7.20 x 10(15) cm(-3) eV(-1) and 7.56 x 10(-6) cm, respectively. When the sample was illuminated, the Mott's VRH parameters are altered, particularly, the average hopping distance and the density of states near the Fermi level increase when light intensity increases. This action is attributed to the electron generation by photon absorption, which in turn leads to the Fermi level shift and/or trap density reduction by electron-hole recombination. (C) 2008 Elsevier Ltd. All rights reserved.
Citation - WoS: 12
Citation - Scopus: 12
Interband Transitions in Gallium Sulfide Layered Single Crystals by Ellipsometry Measurements
(Elsevier, 2013) Isik, M.; Gasanly, N. M.; Turan, R.
Spectroscopic ellipsometry measurements on the GaS single crystals are presented in the energy range of 1.2 - 6.2 eV at room temperature. Optical constants; pseudorefractive index, pseudoextinction coefficient, real and imaginary parts of the pseudodielectric function were determined. Analysis of the second derivative of real and imaginary parts of the pseudodielectric constant revealed five transitions with critical point energies of 3.95, 4.22, 4.51, 4.75 and 5.50 eV. These energies were assigned to interband transitions according to theoretical study of GaS band structure available in literature. (C) 2012 Elsevier B.V. All rights reserved.
Low Temperature Thermoluminescence of Quaternary Thallium Sulfide Tl₄inga_3<
(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.
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.
Citation - WoS: 3
Citation - Scopus: 4
Optical Properties of Cu₃in_{5< 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.
Citation - WoS: 2
Determination of Optical Constants and Temperature Dependent Band Gap Energy of Gas_0.25se_{0.75< 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.
Citation - WoS: 8
Citation - Scopus: 8
Study of Vibrational Modes in (ga₂s_{3< - (ga₂se_{3< 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.
Citation - WoS: 7
Citation - Scopus: 7
Photoconductivity Kinetics in Agin₅s_{8< Thin Films}
(Elsevier Science Sa, 2010) Qasrawi, A. F.; Kayed, T. S.; Ercan, Ismail
The temperature (T) and illumination intensity (F) effects on the photoconductivity of as grown and heat-treated AgIn5S8 thin films has been investigated. At fixed illumination intensity, in the temperature region of 40-300K, the photocurrent (I-ph) of the films was observed to decrease with decreasing temperature. The I-ph of the as grown sample behaved abnormally in the temperature region of 170-180K. At fixed temperature and variable illumination intensity, the photocurrent of the as grown sample exhibited linear, sublinear and supralinear recombination mechanisms at 300 K and in the regions of 160-260K and 25-130 K. respectively. This behavior is attributed to the exchange of role between the linear recombination at the surface near room temperature and trapping centers in the film which become dominant as temperature decreases. Annealing the sample at 350 K for 1 h improved the characteristic curves of I-ph. The abnormality disappeared and the I-ph - T dependence is systematic. The data analysis of which revealed two recombination centers located at 66 and 16 meV. In addition, the sublinear recombination mechanism disappeared and the heat-treated films exhibited supralinear recombination in most of the studied temperature range. (C) 2010 Elsevier B.V. All rights reserved.
Citation - WoS: 8
Citation - Scopus: 9
Electronic, Optical and Thermodynamic Characteristics of Bi12sio20 Sillenite: First Principle Calculations
(Elsevier Science Sa, 2021) Isik, M.; Surucu, G.; Gencer, A.; Gasanly, N. M.
Bi12XO20 (X: Si, Ge, Ti) ternary semiconducting compounds are known as sillenites and take a remarkable attention thanks to their attractive photorefractive properties. The present paper reports electronic, optical and thermodynamic characteristics of Bi12SiO20 by means of density functional theory (DFT) calculations. The crystalline structure of the compound was revealed as cubic with lattice constant of 10.135 angstrom. XRD pattern obtained from DFT calculations were compared with experimental data and there is a good consistency between them. The electronic band structure and density of state plots were presented in detail. The band gap energy of the compound was determined from electronic band structure and spectra of optical constants. The spectral dependencies of real and imaginary components of dielectric function, refractive index, extinction coefficient, absorption coefficient and loss function were plotted in the 0-12 eV spectral range. The revealed structural, electronic and optical characteristics were discussed taking into account the previously reported theoretical and experimental studies on the Bi12SiO20 sillenite.

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