9 results
Search Results
Now showing 1 - 9 of 9
Article Citation - WoS: 5Citation - Scopus: 5Absorption Edge and Optical Constants of Tl2ga2< Crystals From Reflection and Transmission, and Ellipsometric Measurements(Elsevier, 2012) Isik, M.; Gasanly, N. M.The optical properties of Tl2Ga2S3Se layered crystalline semiconductors were investigated from transmission, reflection and ellipsometric measurements. The experimental results of the room temperature transmission and reflection measurements performed in the wavelength range of 400-1100 nm showed the presence of both indirect and direct transitions in the band structure of the crystals with 2.38 and 2.62 eV band gap energies. Spectroscopic ellipsometry measurements on Tl2Ga2S3Se crystals were carried out on the layer-plane (0 0 1) surfaces with light polarization E perpendicular to c* in the 1.20-4.70 eV spectral range at room temperature. The real and imaginary parts of the dielectric function as well as refractive and absorption indices were found as a result of analysis of ellipsometric data. The Wemple-DiDomenico single-effective-oscillator model was used to study the dispersion of the refractive index in the below band gap energy range. The structures of critical points have been characterized from the second derivative spectra of the dielectric function. The analysis revealed four interband transition structures with 3.14, 3.40, 3.86 and 4.50 eV critical point energies. (C) 2012 Elsevier B.V. All rights reserved.Article Citation - WoS: 12Citation - Scopus: 12Interband 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.Article Citation - WoS: 7Citation - Scopus: 7Exploring the Linear and Nonlinear Optical Behavior of (tlins2)0.75(tlinse2)0.25: Insights From Ellipsometry Measurements(Elsevier, 2023) Isik, M.; Guler, I.; Gasanly, N.The search for layered structured new semiconductor materials with remarkable optical properties has become a driving force, especially for materials science. Tl2In2S3Se [(TlInS2)0.75(TlInSe2)0.25], a fascinating compound, holds great promise for advanced photonic and optoelectronic applications. In the present study, the linear and nonlinear optical properties of Tl2In2S3Se layered single crystals were studied by ellipsometry measurements. The variation of refractive index, extinction coefficient, absorption coefficient and skin depth with energy were investigated. Applying the derivative analysis technique to the absorption spectrum, indirect bandgap was found as 2.19 eV. The refractive index data was analyzed considering single-effective-oscillator model. The lattice dielectric constant, plasma frequency, carrier density to the effective mass ratio and zero-frequency refractive index were found. Moreover, the change in optical conductivity with energy yielded to determine the direct bandgap as 2.40 eV. The optical parameters of nonlinear refractive index, first-and third-order nonlinear susceptibilities were also reported.Article Citation - WoS: 11Citation - Scopus: 11Ellipsometry Study of Interband Transitions in Tlgas2x< Mixed Crystals (0 ≤ x ≤ 1)(Elsevier, 2012) Isik, M.; Gasanly, N. M.In this paper, the spectroscopic ellipsometry measurements on TlGaS2xSe2(1 - x) mixed crystals (0 <= x <= 1) were carried out on the layer-plane (001) surfaces with light polarization E perpendicular to c* in the 1.2-6.2 eV spectral range at room temperature. The real and imaginary parts of the dielectric function, refractive index and extinction coefficient were calculated from ellipsometric data using the ambient-substrate optical model. The critical point energies in the above-band gap energy range have been obtained from the second derivative spectra of the dielectric function. Particularly for TlGaSe2 crystals, the determined critical point energies were assigned tentatively to interband transitions using the available electronic energy band structure. The effect of the isomorphic anion substitution (sulfur for selenium) on critical point energies in TlGaS2xSe2(1 - x) mixed crystals was established. (C) 2012 Elsevier B.V. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 6Spectroscopic Ellipsometry Characterization of Pbwo4 Single Crystals(Elsevier, 2022) Delice, S.; Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.Optical characterization of PbWO4 single crystals grown by Czochralski method was achieved in virtue of spectroscopic ellipsometry experiments carried out in the energy region of 1.0-5.6 eV at room temperature. Tetragonal scheelite structure with lattice parameters of a = b = 5.4619 & Aring; and c = 12.0490 & Aring; was determined for the bulk crystal utilizing from XRD analysis. Analyses of the ellipsometry data presented the photon energy dependencies of complex dielectric function of the crystal. The real part of the dielectric function exhibited increasing behavior with energy in the below 4.1 eV and then decreased immediately. Zero frequency refractive index and dielectric constant were determined to be 2.02 and 4.08, respectively, using Wemple and DiDomenico oscillator model. High frequency dielectric constant was calculated as 4.30 by Spitzer-Fan model. Optical band gap of PbWO4 was found to be 3.24 eV from the dielectric relaxation time spectrum. Moreover, existence of two critical points with energies of 3.70 and 4.58 eV was revealed from the analyses of extinction coefficient and second derivative of the dielectric function. These levels were considered to be due to creation of cation exciton (Pb2+ 6s(2) - Pb2+ 6s6p) and transitions in the [WO4](2-) group.Article Citation - WoS: 11Citation - Scopus: 12Characterization of Au/As2< Hybrid Devices Designed for Dual Optoelectronic Applications(Elsevier, 2020) Kayed, T. S.; Qasrawi, A. F.In this work, hybrid devices composed of n-As2Se3/p-MoO3 encapsulated between two Schottky shoulders (Au/n-As2Se3, Ag/MoO3) are prepared and characterized. While the structural analyses proofed the preferred growth of monoclinic MoO3 onto amorphous layers of As2Se3, the spectroscopic ellipsometry analysis revealed the high frequency dielectric constants, the effective mass and the negative pseudodielectric constant values. Electrically, the hybrid device displayed both tunneling and standard diode characteristics. As passive mode devices, the capacitance-voltage characteristics displayed the accumulation-depletion -inversion modes in the device. Furthermore, the conductivity spectral analysis has shown that the current conduction is dominated by the quantum mechanical tunneling and correlated barriers hoping mechanisms. The amplitude of the reflection coefficient and the return loss spectral analyses indicated that the hybrid devices are band stop filters in addition to it is usability as nonlinear optical interfaces, CMOS device and tunneling diodes.Article Citation - WoS: 10Citation - Scopus: 10Ellipsometry Study of Optical Parameters of Agin5s8< Crystals(Elsevier, 2015) Isik, Mehmet; Gasanly, NizamiAgln(5)S(8) crystals grown by Bridgman method were characterized for optical properties by ellipsometry measurements. Spectral dependence of optical parameters; real and imaginary parts of the pseudodielectric function, pseudorefractive index, pseudoextinction coefficient, reflectivity and absorption coefficient were obtained from ellipsometiy experiments carried out in the 1.2-6.2 eV range. Direct band gap energy of 1.84 eV was found from the analysis of absorption coefficient vs. photon energy. The oscillator energy, dispersion energy and zero-frequency refractive index, high-frequency dielectric constant values were found from the analysis of the experimental data using Wemple-DiDomenico and Spitzer-Fan models. Crystal structure and atomic composition ratio of the constituent elements in the AgIn5S8 crystal were revealed from structural characterization techniques of X-ray diffraction and energy dispersive spectroscopy. (C) 2015 Elsevier B.V. All rights reservedArticle Citation - WoS: 13Citation - Scopus: 16Unveiling the Application Potential of Pbmo0.75w0.25< Crystal: Linear and Nonlinear Optical Properties Through Ellipsometry(Elsevier, 2024) Isik, M.; Gasanly, N. M.PbMo0.75W0.25O4 compound is formed by replacing one quarter of the Mo atoms in the PbMoO4 with W atoms and has significant potential for optoelectronic applications. Optical properties of PbMo0.75W0.25O4 single crystal have been systematically investigated using ellipsometry measurements in the spectral range of 2.4-5.4 eV. The linear optical parameters, including refractive index, extinction coefficient, and absorption coefficient, were extracted from the obtained ellipsometry data. By analyzing spectral dependence of these parameters, band gap energy, critical point energy, and single effective oscillator parameters were determined. The refractive index spectrum was analyzed in the below band gap energy region by considering Cauchy and Sellmeier models. Additionally, nonlinear optical values were calculated, providing a comprehensive understanding of the optical properties of the PbMo0.75W0.25O4 single crystal. This study not only contributes to the fundamental understanding of the crystal's optical properties but also has potential implications for applications in optoelectronic devices and photovoltaics.Article Citation - WoS: 3Citation - Scopus: 2Characterization of Linear and Nonlinear Optical Properties of Nabi(wo4)2 Crystal by Spectroscopic Ellipsometry(Elsevier, 2024) Isik, M.; Işık, Mehmet; Guler, I.; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringNaBi(WO4)2 compound has been a material of considerable attention in optoelectronic applications. The present research, in which we examined the linear and nonlinear optical properties of NaBi(WO4)2 crystal using the spectroscopic ellipsometry method, elucidates the optical behavior of the crystal in detail. Our work provides a sensitive approach to determine the spectral characteristic of the crystal. The spectral dependence of various optical parameters such as refractive index, extinction coefficient, dielectric function and absorption coefficient was reported in the range of 1.2-5.0 eV. Optical values such as bandgap energy, critical point energy, single oscillator parameters were obtained as a result of the analyses. In addition to linear optical properties, we also investigated the nonlinear optical behavior of NaBi(WO4)2 and shed new light on the potential applications of the crystal. Absorbance and photoluminescence spectra of the crystal were also reported to characterize optical, electronic and emission behavior of the compound. Our findings may form the basis for a number of technological applications such as optoelectronic devices, frequency conversion, and optical sensors. This research contributes to a better understanding of the optical properties of NaBi(WO4)2 crystal, highlighting the material's role in future optical and electronic technologies.
