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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: 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: 1Citation - Scopus: 1Temperature -Dependent Optical and Electrical Characterization of Cu-Ga Thin Films and Their Diode Characteristics on N-Si(Elsevier Gmbh, 2020) Gullu, H. H.; Isik, M.; Gasanly, N. M.; Parlak, M.In this paper, optical and electrical properties of thermally deposited Cu-Ga-S thin films were investigated using temperature-dependent optical transmission and electrical conductivity measurements. The analysis of the transmission spectra resulted in formation of three direct optical transitions due to the possible valence band splitting in the structure. The band gap values were calculated by means of absorption coefficient and incident photon energy was found in decreasing behavior as the temperature rises. The measured current-voltage values were used to extract the conductivity values which stand in the range of 1.73-2.62 (x104 O-1 cm-1) depending on the ambient temperature. These dark conductivity values were modeled by thermionic emission mechanism. The conductivity activation energies in the structures were calculated as 6.4, 14.5 and 40.7 meV according to the effects of grain boundary potentials. In addition, the films deposited on n-Si wafer showed a diode characteristic under the applied bias voltage between indium (In) front and silver (Ag) back contacts. From current-voltage measurements across the Si-based diode, about four orders of magnitude rectification was observed and the results were analyzed to determine the main diode parameters at dark and room temperature conditions.Article Citation - WoS: 5Citation - Scopus: 5Structural and Optical Properties of Thermally Evaporated (gase)0.75-(gas)0.25 Thin Films(Elsevier Gmbh, 2021) Isik, M.; Işık, Mehmet; Emir, C.; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringGaSe and GaS binary semiconducting compounds are layered structured and have been an attractive research interest in two-dimensional material research area. The present paper aims at growing (GaSe)0.75 - (GaS)0.25 (or simply GaSe0.75S0.25) thin film and investigating its structural and optical properties. Thin films were prepared by thermal evaporation technique using evaporation source of its single crystal grown by Bridgman method. The structural properties were revealed using x-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. XRD pattern and EDS analyses indicated that thin films annealed at 300 ?C were successfully deposited and its structural characteristics are well-consistent with its single crystal form. Surface morphology was studied by means of SEM and AFM measurements. Optical properties were investigated by transmission and Raman spectroscopy techniques. Raman spectrum exhibited three peaks around 172, 242 and 342 cm-1. Analyses of transmission spectrum revealed the direct band gap energy as 2.34 eV. The mixed compounds of GaSe0.75S0.25 were prepared for the first time in a thin film form and the results of the present paper would provide valuable information to research area in which layered compounds have been studied in detail.Article Citation - WoS: 1Citation - Scopus: 1Optical Parameters of Anisotropic Chain-Structured Tl2ingate4< Crystals by Spectroscopic Ellipsometry(Elsevier Gmbh, 2016) Isik, M.; Gasanly, N. M.Spectroscopic ellipsometry measurements were performed on Tl2InGaTe4 single crystals in the 1.2-6.2 eV range for orientations of electric field, parallel (E//c) and perpendicular (E perpendicular to c) to optic axis c. Spectral dependence of optical parameters; real and imaginary components of the dielectric function, refractive index and extinction coefficient were obtained from the analyses of experimental data using an ambient-substrate optical model. The analysis of the absorption data calculated using the extinction coefficient showed the existence of indirect transitions in the crystal with an energy band gap of similar to 0.72 eV for both orientations. Interband transition (critical point) energies were revealed using second-energy derivative spectra of the dielectric function. The results showed the presence of five each interband transition structures for E//c and E perpendicular to c orientations. (C) 2016 Elsevier GmbH. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 7Temperature dependent bandgap in NaBi(WO4)2 single crystals(Elsevier Gmbh, 2022) Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.The double tungstates have been an attractive research interest due to their optoelectronic applications. In the present work, NaBi(WO4)(2), one of the members of double tungstates family, was grown by Czochralski method as single crystal form and optically investigated. X-ray diffraction pattern presented three peaks associated with tetragonal scheelite crystalline structure. Optical properties of the crystal were studied by performing temperature-dependent transmission measurements between 10 and 300 K. The shift of the absorption edge to higher energies was observed with decrease of temperature. The analyses indicated that direct band gap energy increases from 3.50 to 3.60 eV when the temperature was decreased from room temperature to 10 K. The temperature dependency of bandgap was studied considering the Varshni model and fitting of the experimental data under the light of model presented the optical parameters of band gap energy at 0 K, rate of band gap change with temperature and Debye temperature as E-g(0) = 3.61 eV, gamma = 8.83 x 10(-4) eV/K and beta = 456 K, respectively. Urbach energies were also determined from the analyses as 122 and 113 meV for 10 and 300 K experimental data, respectively.Article Citation - WoS: 7Citation - Scopus: 6Investigation of Optical Characteristics of Pbmoo4 Single Crystals by Spectroscopic Ellipsometry(Elsevier Gmbh, 2022) Delice, S.; Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.In this study, we investigated the optical properties of PbMoO4 single crystals grown by Czochralski method. Spectroscopic ellipsometry measurements were carried out in the energy region between 1.0 and 5.5 eV at room temperature. X-ray diffraction measurements were achieved for structural characterization. The resulted pattern exhibited one peak belonging to (200) plane. Spectral variations of complex dielectric function, complex refractive index, absorption coefficient and dissipation function were obtained from the analyses of ellipsometry data. Real part of dielectric function increased up to 4.0 eV and then decreased suddenly at above this value. Zero frequency refractive index and dielectric constant were found to be 2.04 and 4.15, respectively. High frequency dielectric constant was determined to be 4.36. Optical band gap of PbMoO4 crystals was calculated as 3.09 eV. Two critical points with energies of 3.57 and 4.34 eV were estimated from the analyses of second-energy derivative spectra of real and imaginary parts of dielectric function. It was determined that [MoO4]2- complexes and charge transfer from Pb2+ ions into the neighboring Mo groups were responsible for these interband transitions. Dissipation function increased with increasing photon energy.Article Citation - WoS: 8Citation - Scopus: 8Characterization of Trap Centers in Gd2o3< Nanoparticles by Low Temperature Thermoluminescence Measurements(Elsevier Gmbh, 2018) Delice, S.; Isik, M.; Gasanly, N. M.Trapping centers in Gd2O3 nanoparticles were investigated using thermoluminescence (TL) measurements in the below room temperature region of 10-280 K. Seven peaks having peak maximum temperatures between 30 and 252 K were observed in the TL spectra measured at constant heating rate of 0.3 K/s. Activation energies, order of kinetics and frequency factors were reported using three different analysis techniques: curve fitting, initial rise and peak shape methods. Activation energies of the trapping centers were found between 0.012 eV and 0.79 eV. Most of the TL transitions associated with observed peaks were found as dominated by mixed order of kinetics. Structural characterization of used nanoparticles was achieved using x-ray diffraction and scanning electron microscopy experiments. (C) 2017 Elsevier GmbH. All rights reserved.
