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Article Citation - WoS: 4Citation - Scopus: 4Mixed Conduction and Anisotropic Single Oscillator Parameters in Low Dimensional Tlinse2 Crystals(Elsevier Science Sa, 2013) Qasrawi, A. F.; Gasanly, N. M.Due to the importance of the TlInSe2 crystal as neutron and gamma-ray detectors, its electrical and dispersive optical parameters have been investigated. Particularly, the anisotropic current conduction mechanism in the temperature region of 100-350 K and the room temperature anisotropic dispersive optical properties were studied by means of electrical conductivity and optical reflectance, respectively. It has been shown that the mixed conduction is the most dominant transport mechanism in the TlInSe2 crystals. Particularly, when the electric field is applied perpendicular to the crystal's c-axis, the main dominant current transport mechanism is due to the mixed conduction and the variable range hopping above and below 160 K, respectively. When the electric field is applied parallel to the crystal's c-axis, the electrical conductivity is dominated by the thermionic emission, mixed conduction and variable range hopping at high, moderate and low temperatures, respectively. The optical reflectivity analysis in the wavelength range 210-1500 nm revealed a clear anisotropy effect on the dispersive optical parameters. Particularly, the static refractive index, static dielectric constant, dispersion energy and oscillator energy exhibited values of 2.50, 6.24, 20.72 eV and 3.96 eV, and values of 3.05, 9.33, 39.27 eV and 4.72 eV for light propagation parallel and perpendicular to the crystal's c-axis, respectively. Moreover, the frequency dependence of the dielectric constant, epsilon(omega), reflected strong dielectric anisotropy that exhibit maximum epsilon(omega) value of 38.80 and 11.40 at frequencies of 11.07 x 10(14) Hz for light propagation parallel and perpendicular to the crystal's c-axis, respectively. The anisotropy in the epsilon(omega) makes the TlInSe2 crystals attractive to be used as nonvolatile static memory devices. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 13Citation - Scopus: 14Linear and Nonlinear Optical Properties of Bi12geo20 Single Crystal for Optoelectronic Applications(Elsevier Sci Ltd, 2023) Isik, M.; Gasanly, N. M.The present paper aims at presenting linear and nonlinear optical properties of Bi12GeO20 single crystals grown by Czochralski method. Transmission and reflection measurements were performed in the 400-1000 nm region. The recorded spectra were analyzed considering well-known optical models. Spectral dependencies of absorption coefficient, skin depth, refractive index, real and imaginary components of dielectric function were presented. The analyses performed on absorption coefficient showed direct bandgap and Urbach energies as 2.56 and 0.22 eV, respectively. The first-and third-order nonlinear susceptibilities and nonlinear refractive index of the crystal were also reported in the present work. The results of the present paper would provide valuable information for optoelectronic device applications of Bi12GeO20.Article Citation - WoS: 22Citation - Scopus: 24Synthesis and Temperature-Tuned Band Gap Characteristics of Magnetron Sputtered Znte Thin Films(Elsevier, 2020) Isik, M.; Gullu, H. H.; Parlak, M.; Gasanly, N. M.Zinc telluride (ZnTe) is one of the attractive semiconducting compounds used in various optoelectronic devices. The usage of ZnTe in optoelectronic applications directs researchers to search its optical characteristics in great detail. For this purpose, structural and optical properties of magnetron sputtered ZnTe thin films were studied by means of x-ray diffraction and transmission spectroscopy measurements. Structural analyses indicated that ZnTe thin films having cubic crystalline structure were successfully grown on soda-lime glass substrates. Transmittance spectra in the 400-1000 nm were recorded in between 10 and 300 K temperature region. The analyses of absorption coefficient spectra resulted in band gap energies decreasing from around 2.31 (10 K) to 2.26 eV (300 K). Temperature dependency of gap energy was studied by Varshni and O'Donnell-Chen relations to determine various optical parameters like absolute zero temperature band gap energy, change of gap energy with temperature, phonon energy.Article Citation - WoS: 3Citation - Scopus: 4Optical 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.Article Citation - WoS: 7Citation - Scopus: 7In situ monitoring of the permanent crystallization, phase transformations and the associated optical and electrical enhancements upon heating of Se thin films(Elsevier Science Bv, 2019) Qasrawi, A. F.; Aloushi, Hadil D.In this work, the in situ structural transformations from amorphous to polycrystalline upon heating and the associated enhancements in the structural parameters of selenium thin films are studied by means of X-ray diffraction technique. The Se thin films which are grown onto ultrasonically cleaned glass substrate by the thermal evaporation technique under vacuum pressure of 10(-5) mbar exhibits structural transformation from amorphous to polycrystalline near 353 K. The films completed the formation of the structure which includes both of the hexagonal and monoclinic phases at 363 K. It is observed that the hexagonal phase dominates over the monoclinic as temperature is raised. Consistently, the thermally assisted crystallization process is accompanied with increase in the crystallite size, decrease in the microstrain, decrease in defect density and decrease in the percentage of stacking faults. The scanning electron microscopy measurements also confirmed the crystallinity of selenium after heating. The time dependent reputations of the crystallization test has shown that the achieved phase transitions and enhancements in structural parameters are permanent in selenium. Optically, the crystallization process is observed to be associated with redshift in the absorption spectra and in the value of the energy band gap. Electrically, the in situ monitoring of the electrical conductivity during the heating cycle has shown that the electrical conductivity stabilizes and exhibit a decrease in the acceptor levels from 566 to 321 meV after the crystallization was achieved.Article Citation - WoS: 3Citation - Scopus: 6Structural and Optical Properties of Thermally Evaporated Cu-Ga (cgs) Thin Films(Elsevier, 2018) Gullu, H. H.; Isik, M.; Gasanly, N. M.The structural and optical properties of thermally evaporated Cu-Ga-S (CGS) thin films were investigated by Xray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM) and optical transmittance measurements. The effect of annealing temperature on the results of applied techniques was also studied in the present paper. EDS results revealed that each of the elements, Cu, Ga and S are presented in the films and Cu and Ga concentration increases whereas S concentration decreases within the films as annealing temperature is increased. XRD pattern exhibited four diffraction peaks which are well-matched with those of tetragonal CuGaS2 compound. AFM images were recorded to get knowledge about the surface morphology and roughness of deposited thin films. Transmittance measurements were applied in the wavelength region of 300-1000 nm. Analyses of the absorption coefficient derived from transmittance data resulted in presence of three distinct transition regions in each thin films with direct transition type. Crystal-field and spin-orbit splitting energies existing due to valence band splitting were also calculated using quasicubic model.Article Citation - WoS: 9Citation - Scopus: 9Optical Band Gap and Dispersion of Optical Constants of Cu-Ga Thin Films(Elsevier Gmbh, 2019) Isik, M.; Gullu, H. H.; Coskun, E.; Gasanly, N. M.Thermally deposited Cu-Ga-S thin films were optically characterized by means of experimental techniques of transmission measurements. The analyses of transmittance spectra were accomplished by derivative spectrophotometry analyses to get gap energies of thin films. The transmittance spectra of thin films annealed at different temperatures presented interference fringes which were analyzed by Swanepoel envelope method. The wavelength dependencies of optical parameters; refractive index (n), real part of complex dielectric function (epsilon(re)) and extinction coefficient (k) were reported in the weak absorption region. The photon energy dependencies of n and epsilon(re) were analyzed using single-oscillator and Spitzer-Fan models, respectively.Article Citation - WoS: 8Citation - Scopus: 9Electronic, 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.Article Citation - WoS: 2Citation - Scopus: 2Optical Characterization of Nabi(moo4)2< Crystal by Spectroscopic Ellipsometry(Springer Heidelberg, 2024) Guler, I.; Isik, M.; Gasanly, N. M.The compound NaBi(MoO4)(2) has garnered significant interest in optoelectronic fields. This study employs spectroscopic ellipsometry to thoroughly examine the linear and nonlinear optical characteristics of NaBi(MoO4)(2) crystals, offering detailed insights into their optical behavior. Our investigation presents a precise method for discerning the crystal's spectral features, revealing the spectral variations of key optical parameters such as refractive index, extinction coefficient, dielectric function, and absorption coefficient within the 1.2-5.0 eV range. Through analysis, we determined optical attributes including bandgap energy, critical point energy, and single oscillator parameters. Additionally, we explored the nonlinear optical properties of NaBi(MoO4)(2), unveiling potential applications such as optoelectronic devices, frequency conversion, and optical sensors. This study enhances comprehension of optical properties of NaBi(MoO4)(2), underscoring its significance in future optical and electronic advancements.Article Citation - WoS: 4Citation - Scopus: 4Growth and Optical Characterization of Sn0.6sb0.4< Layer Single Crystals for Optoelectronic Applications(Elsevier Sci Ltd, 2022) Bektas, T.; Terlemezoglu, M.; Surucu, O.; Isik, M.; Parlak, M.SnSe compound is an attractive semiconductor material due to its usage in photovoltaic applications. The sub-stitution of Sb in the SnSe compound presents a remarkable advantage especially in point of tuning optical characteristics. The present paper reports the structural and optical properties of Sn1-xSbxSe (x = 0.4) layered single crystals grown by the vertical Bridgman method. To the best of our knowledge, this work is the first investigation of the Sn0.6Sb0.4Se crystal grown with the vertical Bridgman technique. X-ray diffraction (XRD) pattern of the grown crystal indicated the well crystalline structure of the grown crystals. Lattice strain and interplanar spacing of the crystal structure were determined using the XRD pattern. Scanning electron micro-scope images allowed to the observation of the layer crystal structure. The layer crystalline structure shows 2D material properties and provides 2D applications. Optical properties were revealed by carrying out Raman, ellipsometry and transmission measurements. Raman modes, refractive index, extinction coefficient, and dielectric spectra, band gap energy of the crystal were presented throughout the paper. The obtained results indicated that Sn1-xSbxSe (x = 0.4) layer single crystals may be an alternative potential for photovoltaic and optoelectronic applications.
