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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.
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.
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: 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.
Citation - WoS: 2
Citation - Scopus: 2
Structural, Electrical and Anisotropic Properties of Tl₄se_{3< Chain Crystals}
(Pergamon-elsevier Science Ltd, 2009) Qasrawi, A. F.; Gasanly, N. M.
The structure, the anisotropy effect on the current transport mechanism and the space charge limited current in Tl4Se3S chain crystals have been studied by means of X-ray diffraction, electrical conductivity measurements along and perpendicular to the crystal's c-axis and the current voltage characteristics. The temperature-dependent electrical conductivity analysis in the region of 150-400 K, revealed the domination of the thermionic emission of charge carriers over the chain boundaries above 210 and 270 K along and perpendicular to the c-axis, respectively. Below these temperatures, the variable range hopping is dominant. At a consistent temperature range, the thermionic emission analysis results in conductivity activation energies of 280 and 182 meV, along and perpendicular to the c-axis, respectively. Likewise, the hopping parameters are altered significantly by the conductivity anisotropy. The current-voltage characteristics revealed the existence of hole trapping state being located at 350 meV above the valence band of the crystal. (C) 2009 Elsevier Ltd. All rights reserved.
Citation - WoS: 29
Citation - Scopus: 31
Composition-tuned band gap energy and refractive index in GaS_xSe_1-x layered mixed crystals
(Elsevier Science Sa, 2017) Isik, Mehmet; Gasanly, Nizami
Transmission and reflection measurements on GaSxSe1-x mixed crystals (0 <= x <= 1) were carried out in the 400-1000 nm spectral range. Band gap energies of the studied crystals were obtained using the derivative spectra of transmittance and reflectance. The compositional dependence of band gap energy revealed that as sulfur (selenium) composition is increased (decreased) in the mixed crystals, band gap energy increases quadratically from 1.99 eV (GaSe) to 2.55 eV (GaS). Spectral dependencies of refractive indices of the mixed crystals were plotted using the reflectance spectra. It was observed that refractive index decreases nearly in a linear behavior with increasing band gap energy for GaSxSe1-x mixed crystals. Moreover, the composition ratio of the mixed crystals was obtained from the energy dispersive spectroscopy measurements. The atomic compositions of the studied crystals are well-matched with composition x increasing from 0 to 1 by intervals of 0.25. (C) 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 1
Dark Electrical Conductivity and Photoconductivity of Ga₄se_{3< Layered Single Crystals}
(Pergamon-elsevier Science Ltd, 2008) Qasrawi, A. F.; Gasanly, N. M.
Ga(4)Se(3)S layered crystals were studied through the dark electrical conductivity, and illumination- and temperature-dependent photoconductivity in the temperature region of 100-350 K. The dark electrical conductivity reflected the existence of two energy states located at 3 10 and 60 meV being dominant above and below 170 K, respectively. The photoconductivity measurements revealed the existence of another two energy levels located at 209 and 91 meV above and below 230 K. The photoconductivity was observed to increase with increasing temperature. The illumination dependence of photoconductivity was found to exhibit linear and supralinear recombination above and below 280 K, respectively. The change in recombination mechanism was attributed to the exchange in the behavior of sensitizing and recombination centers. (C) 2008 Elsevier Ltd. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Analysis of Optical Constants and Temperature-Dependent Absorption Edge of Gas_0.75se_{0.25< Layered Crystals}
(Pergamon-elsevier Science Ltd, 2017) Isik, Mehmet; Gasanly, Nizami
GaS0.75Se0.25 single crystals were optically characterized through transmission and reflection measurements in the wavelength range of 450-1000 nm. Derivative spectrophotometry analyses on temperature dependent transmittance spectra showed that band gap energies of the crystal increase from 239 eV (T=300 K) to 2.53 eV (T=10 K). Band gap at zero temperature, average phonon energy, electron phonon coupling parameter and rates of change of band gap energy with temperature were found from the temperature dependences of band gap energies under the light of different models reported in literature. Furthermore, the dispersion of room temperature refractive index was discussed in terms of single effective oscillator model. The refractive index dispersion parameters, namely oscillator and dispersion energies, zero-frequency refractive index, were determined as a result of analyses. (C) 2017 Elsevier Ltd. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 5
Thermoluminescence characteristics of GaSe and Ga₂Se₃single crystals
(Elsevier, 2022) Isik, M.; Sarigul, N.; Gasanly, N. M.
GaSe and Ga2Se3 are semiconducting compounds formed from same constituent elements. These compounds have been attractive due to their optoelectronic and photovoltaic applications. Defects take remarkable attention since they affect quality of semiconductor devices. In the present paper, deep defect centers in GaSe and Ga2Se3 single crystals grown by Bridgman method were reported from the analyses of thermoluminescence measurements performed in the 350-675 K range. Experimental TL curves of GaSe and Ga2Se3 single crystals presented one and two overlapped peaks, respectively. The applied curve fitting and initial rise techniques were in good agreement about trap activation energies of 0.83 eV for GaSe, 0.96 and 1.24 eV for Ga2Se3 crystals. Crystalline structural properties of the grown single crystals were also investigated by x-ray diffraction measurements. The peaks observed in XRD patterns of the GaSe and Ga2Se3 crystals were well-consistent with hexagonal and zinc blende structures, respectively.

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