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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14411/18
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Article Citation - Scopus: 2Material and Device Properties of Si-Based Cu<sub>0.5</Sub>ag<sub>0.5< Thin-Film Heterojunction Diode(Springer, 2019-12-09) Gullu, H. H.; Isik, M.; Delice, S.; Parlak, M.; Gasanly, N. M.Cu0.5Ag0.5InSe2 (CAIS) thin films were deposited on a glass substrate by sequential sputtering of Cu, Ag, and In2Se3-stacked film layers. Structural characterization showed that the deposited CAIS film satisfies nearly the stoichiometric form with uniform and homogeneous surface structure. The single-phase polycrystalline behavior without any secondary-phase formation was observed from the diffraction profile. The optical properties were investigated using temperature-dependent transmission measurements in the wavelength region of 600-1100 nm and in between 10 and 300 K. In the region of interest, the transmission spectra shifted towards the higher wavelengths as a result of an increase in the sample temperature. The analysis of the absorption data based on the transmission spectra resulted in absorption coefficient values of around 10(5) cm(-1) and the presence of direct allowed optical transition. From the Tauc plots, CAIS samples were found to have three distinct direct optical transitions depending on the possible splitting in the valence band. The obtained room temperature uppermost band gap energy value of 1.09 eV was found in the energy limit of ternary analogues (CuInSe2 and AgInSe2), and also in a good agreement with the previous works in the literature. The dependency of the band gap energy on the temperature was analyzed using fundamental relations. In addition, the electrical characteristics of the film layer were discussed in four-contact conductivity measurements, and room temperature conductivity was observed as 0.8 ohm(-1) cm(-1). Additionally, two activation energy values were found in the temperature-dependent conductivity profile. As a diode application, CAIS/Si heterojunction was fabricated and the main diode parameters were extracted at dark and room temperature conditions.Article Citation - WoS: 14Citation - Scopus: 15Structural and Optical Properties of Ga<sub>2</Sub>se<sub>3< Crystals by Spectroscopic Ellipsometry(Springer, 2019-02-06) Guler, I.; Isik, M.; Gasanly, N. M.; Gasanova, L. G.; Babayeva, R. F.Optical and crystalline structure properties of Ga2Se3 crystals were analyzed utilizing ellipsometry and x-ray diffraction (XRD) experiments, respectively. Components of the complex dielectric function (epsilon=epsilon(1)+i epsilon(2)) and refractive index (N=n+ik) of Ga2Se3 crystals were spectrally plotted from ellipsometric measurements conducted from 1.2eV to 6.2eV at 300K. From the analyses of second-energy derivatives of epsilon(1) and epsilon(2), interband transition energies (critical points) were determined. Absorption coefficient-photon energy dependency allowed us to achieve a band gap energy of 2.02eV. Wemple and DiDomenico single effective oscillator and Spitzer-Fan models were accomplished and various optical parameters of the crystal were reported in the present work.Article Citation - WoS: 4Citation - Scopus: 5Analysis of Temperature-Dependent Transmittance Spectra of Zn<sub>0.5</Sub>in<sub>0.5< (zis) Thin Films(Springer, 2019-04-25) Isik, M.; Gullu, H. H.; Delice, S.; Gasanly, N. M.; Parlak, M.Temperature-dependent transmission experiments of ZnInSe thin films deposited by thermal evaporation method were performed in the spectral range of 550-950nm and in temperature range of 10-300K. Transmission spectra shifted towards higher wavelengths (lower energies) with increasing temperature. Transmission data were analyzed using Tauc relation and derivative spectroscopy. Analysis with Tauc relation was resulted in three different energy levels for the room temperature band gap values of material as 1.594, 1.735 and 1.830eV. The spectrum of first wavelength derivative of transmittance exhibited two maxima positions at 1.632 and 1.814eV and one minima around 1.741eV. The determined energies from both methods were in good agreement with each other. The presence of three band gap energy levels were associated to valence band splitting due to crystal-field and spin-orbit splitting. Temperature dependence of the band gap energies were also analyzed using Varshni relation and gap energy value at absolute zero and the rate of change of gap energy with temperature were determined.Article Citation - WoS: 11Citation - Scopus: 11Temperature-Tuned Bandgap Characteristics of Bi<sub>12</Sub>tio<sub>20< Sillenite Single Crystals(Springer, 2020-11-25) Isik, M.; Delice, S.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.Bi12MO20 (M: Si, Ge, Ti, etc.) compounds are known as sillenites having fascinating photorefractive characteristics. The present paper reports the structural and optical characteristics of one of the members of this family, Bi12TiO20 single crystals, grown by Czochralski method. X-ray diffraction pattern of the crystal presented sharp and intensive peaks associated with planes of cubic crystalline structure with lattice constant of a = 1.0142 nm. The optical properties were studied by means of room temperature Raman and temperature-dependent transmission experiments at various temperatures between 10 and 300 K. Raman spectrum indicated peaks around 127, 162, 191, 219, 261, 289, 321, 497 and 537 cm(-1). The analyses of transmittance spectra indicated the increase of direct bandgap energy from 2.30 to 2.56 eV as temperature was decreased from room temperature to 10 K. The temperature-dependent bandgap characteristics of Bi12TiO20 were analyzed by means of Varshni and O'Donnell-Chen models. The analyses under the light of these models resulted in absolute zero bandgap energy of E-g(0) = 2.56(4) eV, rate of change of bandgap energy of gamma = - 1.11 x 10(-3) eV/K and average phonon energy of < E-ph & rang; = 8.6 meV.Article Citation - WoS: 1Citation - Scopus: 3Optical constants and critical point energies of (AgInSe<sub>2</sub>)<sub>0.75</sub>-(In<sub>2</sub>Se<sub>3</sub>)<sub>0.25</sub> single crystals(Springer, 2020-02-11) Isik, M.; Nasser, H.; Guseinov, A.; Gasanly, N. M.AgInSe2 and In2Se3 are two attractive semiconducting materials for various technological applications especially for photovoltaic applications. In the present study, structural and optical properties of (AgInSe2)(x)-(In2Se3)(1-x) crystals for composition of x = 0.75 corresponding to chemical formula of Ag3In5Se9 were characterized by X-ray diffraction, energy-dispersive spectroscopy, room temperature transmission, and ellipsometry experiments. The transmittance spectrum was analyzed to reveal energy band gap. The derivative spectrophotometry analysis resulted in band gap energy of 1.22 eV. The spectra of complex dielectric function, refractive index and extinction coefficient were presented between 1.6 and 6.2 eV from the outcomes of ellipsometry analyses. Critical point energies have been determined using the derivative analyses of dielectric function. Five critical points at 2.70, 3.30, 4.05, 4.73, and 5.42 eV were revealed from the analyses. Crystal structure and atomic composition in semiconducting compound were also reported in the present work. The obtained results were compared with those reported for constituent compounds.Article Citation - WoS: 12Citation - Scopus: 12Material and Si-based diode analyses of sputtered ZnTe thin films(Springer, 2020-05-29) Gullu, H. H.; Surucu, O. Bayrakli; Isik, M.; Terlemezoglu, M.; Parlak, M.Structural, optical, and electrical properties ZnTe thin films grown by magnetron sputtering technique were studied by X-ray diffraction, atomic force microscopy, Raman spectroscopy, and electrical conductivity measurements. Structural analyses showed that ZnTe thin films grown on soda-lime glass substrates have a cubic crystalline structure. This crystalline nature of the films was also discussed in terms of Raman active modes. From atomic force microscopy images, the smooth and dense surface profile was observed. The conductivity of the film at room temperature was measured as 2.45 x 10(-4)(omega cm)(-1)and the temperature dependency of conductivity showed Arrhenius behavior. The dark conductivity profile was modeled by thermionic emission mechanism and activation energies were extracted. In addition, the conductivity values indicated an increasing behavior with illumination intensity applied between 20 and 115 mW/cm(2). The heterojunction diode was generated by sputtering ZnTe film on n-Si wafer substrate and the rectification behavior was evaluated to determine the main diode parameters.Article Citation - WoS: 6Citation - Scopus: 6Vibrational Modes in (tlgas<sub>2</Sub>)<sub><i>x< Crystals by Raman Measurements: Compositional Dependence of the Mode Frequencies and Line-Shapes(Springer, 2020-07-13) Isik, M.; Terlemezoglu, M.; Gasanly, N. M.; Babayeva, R. F.TlGaS(2)and TlGaSe(2)ternary semiconducting compounds have been of scientific interest due to their large ultrafast optical nonlinearity characteristics. These remarkable properties make them promising semiconducting materials in photonic applications. A series of (TlGaS2)(x)-(TlGaSe2)(1-x)layered mixed crystals grown by Bridgman method were investigated from the standpoint of their Raman spectroscopy characteristics. Experimental Raman scattering study of crystals were reported in the frequency range of 80-400 cm(-1)for compositions ofx = 0, 0.25, 0.50, 0.75 and 1.0. The effects of crystal disorder on the line-width broadening of Raman-active modes were studied in detail. The asymmetry in the Raman line-shape was analyzed for two highest-frequency intralayer mode presenting two-mode behavior. It was shown that mixed crystal disorder effect is the major source for change of Raman line-shape with composition.Article Citation - WoS: 4Citation - Scopus: 6Structural and Optical Properties of (tlins<sub>2</Sub>)<sub>0.75< Thin Films Deposited by Thermal Evaporation(Springer, 2023-01) Guler, I.; Isik, M.; Gasanly, N.Layered semiconductor materials have become a serious research topic in recent years, thanks to their effective optical properties. In this article, the thin-film structure of Tl2In2S3Se [(TlInS2)(0.75)(TlInSe2)(0.25)] material with layered structure was grown by thermal evaporation method. The structural, morphological, and optical properties of the deposited thin films were examined. X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and atomic force microscopy (AFM) techniques were used to get information about structural and morphological properties of the thin films. XRD pattern presented well-defined peaks associated with monoclinic crystalline structure. The crystallite size, dislocation density, and lattice strain of the films were also obtained from the analyses of XRD pattern. EDS analysis showed that atomic compositional ratios of the Tl, In, S, and Se elements are consistent with chemical formula of Tl2In2S3Se. The optical characterization of thin film was performed using transmission and Raman spectroscopy techniques. Raman spectrum offered information about the vibrational modes of the thin film. The analyses of the transmission spectrum presented the indirect and direct band gap energies of the Tl2In2S3Se thin film as 2.23 and 2.52 eV, respectively. The further analyses on the absorption coefficient resulted in Urbach energy of 0.58 eV.Article Citation - WoS: 12Citation - Scopus: 12Linear and Nonlinear Optical Characteristics of Pbmoo<sub>4</Sub> Single Crystal for Optoelectronic Applications(Springer, 2022-09-09) Delice, S.; Isik, M.; Gasanly, N. M.In the present paper, we studied linear and nonlinear optical properties of lead molybdate (PbMoO4) single crystals grown by Czochralski method. Raman measurement was performed in the range of 50-1000 cm(-1) and 11 active vibration modes were defined in the spectrum. The nature of the observed modes was discussed in detail. Optical absorption of the material was investigated utilizing room temperature transmission and reflection experiments in the spectral range of 360-1000 nm. Spectral changes of absorption coefficient, skin depth, refractive index, optical conductivity, and complex dielectric function of PbMoO4 crystals were studied. Absorption coefficient and optical conductivity exhibited strong increment around 3.0 eV with increasing photon energy. Cut-off wavelength was determined to be 390 nm from the skin depth spectrum. Tauc and derivative spectral analyses revealed the presence of direct bandgap with the energy of 3.05 eV. The static refractive index and dielectric constant were estimated as 2.25 and 5.08, respectively, using Wemple-DiDomenico single oscillator model. Urbach energy was calculated to be 0.071 eV from the exponential dependence of absorption coefficient to photon energy. Dielectric constant increased to 5.42 with energy up to 2.60 eV and then it exhibited decreasing behavior. Second energy derivative analysis of imaginary dielectric function resulted in existence of a critical point at 3.19 eV. First- and third-order nonlinear susceptibilities and nonlinear refractive index were found to be 0.32, 1.9 x 10(-12) and 31.7 x 10(-12) esu, respectively. These results show that the material may be used in UV filter and sensor applications.Article Citation - WoS: 1Citation - Scopus: 1Growth and Optical Properties of (na<sub>0.5</Sub>bi<sub>0.5< (x=0.25) Single Crystal: a Potential Candidate for Optoelectronic Devices(Springer, 2023-11-23) Guler, I.; Isik, M.; Gasanly, N.Double tungstates (DT) and double molybdates (DM) have significant importance because of their optoelectronic applications. Regarding the importance of DT and DM, we investigated experimentally structural and optical properties of (Na0.5Bi0.5)(Mo1-xWx)O-4 (x = 0.25) crystal that belongs to the NaBi-DT and DM crystals group. Czochralski method was used to grow the single crystals. The structure of the crystal was identified using X-ray diffraction (XRD) measurements. Two sharp peaks associated with tetragonal crystal structure appeared in the pattern. Vibrational modes of the studied crystal were obtained from the Raman experiments. By the help of the Fourier transform infrared spectrophotometer (FTIR) measurements, infrared transmittance spectrum of the studied compound was recorded. Band gap energy wase found around 3.04 eV using two methods, Tauc and derivative analysis, based on transmission spectrum. Based on the analysis of absorption coefficient, Urbach energy was obtained as 0.22 eV. The revealed structural and optical properties of the crystal indicated that the material may be a candidate for optoelectronic devices in which NaBi(MoO4)(2) and NaBi(WO4)(2) materials are utilized.