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Article Citation - WoS: 12Citation - Scopus: 12Energy Band Gap and Dispersive Optical Parameters in Bi1.5zn0.92< Pyrochlore Ceramics(Elsevier Science Sa, 2010) Qasrawi, A. F.; Mergen, A.The compositional and optical properties of Bi1.5Zn0.92Nb1.5O6.92 Pyrochlore ceramics have been investigated by means of scanning electron microscopy (SEM) and UV-vis spectroscopy, respectively. The SEM spectroscopy revealed that the pyrochlore exhibits a very dense microstructure with single-phase appearance. The absorption spectral analysis in the sharp absorption region revealed an indirect forbidden transitions band gap of 3.30 eV. The room temperature refractive index, which was calculated from the reflectance and transmittance data, allowed the identification of the dispersion and oscillator energies, static and lattice dielectric constants and static refractive index as 26.69 and 3.37 eV, 8.92 and 15.95 and 2.98, respectively. (C) 2010 Elsevier B.V. All rights reserved.Article Citation - WoS: 8Citation - Scopus: 9Structural and Optoelectronic Properties of Cds/Y Thin Films(Elsevier Science Sa, 2019) Qasrawi, A. F.; Abed, Tamara Y.In the current study, the structural, optical, photoelectrical and electrical properties of CdS/Y/CdS thin films are investigated. The current design include the evaporation of a layer of 70 nm thick yttrium between two layers of CdS. Each CdS layer is of thickness of 500 nm. It is observed that the yttrium slab increased the microstrain, defect density, stacking faults and decreased the grain size and redshifts the indirect allowed transitions energy band gap of CdS. In addition an enhancement by similar to 5 times in the light absorbability is detected at 1.74 eV. The enhanced absorbance results in increasing the photocurrent by similar to 21 times and changed the recombination mechanism from a trap assisted recombination to supralinear recombination mechanisms. Moreover, the ac signal analysis in the frequency domain of 10-1800 MHz has shown that the yttrium forces the CdS to exhibit negative capacitance effect and make it behave as band stop filter with notch frequency of 1520 MHz. The quality of the CdS/Y/CdS films as microwave cavities are screened by the evaluation of the return loss which revealed good features of the nanostructured films as microwave receivers.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: 10Citation - Scopus: 11Temperature effects on the optoelectronic properties of AgIn5S8 thin films(Elsevier Science Sa, 2011) Qasrawi, A. F.Polycrystalline AgIn5S8 thin films are obtained by the thermal evaporation of AgIn5S8 crystals onto ultrasonically cleaned glass substrates under a pressure of similar to 1.3 x 10(-3) Pa. The temperature dependence of the optical band gap and photoconductivity of these films was studied in the temperature regions of 300-450 K and 40-300 K, respectively. The heat treatment effect at annealing temperatures of 350, 450 and 550 K on the temperature dependent photoconductivity is also investigated. The absorption coefficient, which was studied in the incidence photon energy range of 1.65-2.55 eV, increased with increasing temperature. Consistently, the absorption edge shifts to lower energy values as temperature increases. The fundamental absorption edge which corresponds to a direct allowed transition energy band gap of 1.78 eV exhibited a temperature coefficient of -3.56 x 10(-4) eV/K. The 0 K energy band gap is estimated as 1.89 eV. AgIn5S8 films are observed to be photoconductive. The highest and most stable temperature invariant photocurrent was obtained at an annealing temperature of 550 K. The photoconductivity kinetics was attributed to the structural modifications caused by annealing and due to the trapping-recombination centers' exchange. (C) 2010 Elsevier B.V. All rights reserved.Conference Object Citation - WoS: 4Citation - Scopus: 3Temperature-dependent material characterization of CuZnSe2 thin films(Elsevier Science Sa, 2020) Gullu, H. H.; Surucu, O.; Terlemezoglu, M.; Isik, M.; Ercelebi, C.; Gasanly, N. M.; Parlak, M.In the present work, CuZnSe2 (CZSe) thin films were co-deposited by magnetron sputtering of ZnSe and Cu targets. The structural analyses resulted in the stoichiometric elemental composition and polycrystalline nature without secondary phase contribution in the film structure. Optical and electrical properties of CZSe thin films were investigated using temperature-dependent optical transmission and electrical conductivity measurements. The band gap energy values were obtained using transmittance spectra under the light of expression relating absorption coefficient to incident photon energy. Band gap energy values were found in decreasing behavior from 2.31 to 2.27 eV with increase in temperature from 10 to 300 K. Temperature-band gap dependency was evaluated by Varshni and O'Donnell models to detail the optical parameters of the thin films. The experimental dark and photoconductivity values were investigated by thermionic emission model over the grain boundary potential. Room temperature conductivity values were obtained in between 0.91 and 4.65 ( x 10(-4) Omega(-1)cm(-1)) under various illumination intensities. Three different linear conductivity regions were observed in the temperature dependent profile. These linear regions were analyzed to extract the activation energy values.Article Citation - WoS: 11Citation - Scopus: 11Post Annealing Effects on the Structural, Compositional, Optical and Dielectric Properties of Cd Doped Gase Thin Films(Elsevier Science Sa, 2015) Al Garni, S. E.; Qasrawi, A. F.In this work, the heat treatment effects at temperatures (T-a) of 200, 300 and 400 degrees C on the compositional, structural, optical and dielectric properties of Cd doped GaSe are explored by means of energy dispersive X-ray spectroscopy, X-ray diffraction and UV-VIS spectrophotometry. The annealing process of the Cd doped GaSe thin films revealed a highly oriented orthorhombic structure type that exhibit a systematic increase in the grain size. While the strain, degree of orientation and dislocation density of the annealed films are weakly affected by the annealing process. The optical energy band gap of the doped films decreased from 1.23 to 0.90 eV and the exponential energy band tails rose from 0.16 to 0.23 eV when the annealing temperature is raised from 300 to 400 degrees C. In addition, the analysis of the dielectric spectral curves which were studied in the frequency range of 270-1500 THz, allowed to investigate the oscillator and dispersion energies and the static (epsilon(s)) and lattice (epsilon(l)) dielectric constants. The annealing process on the doped samples decreased the dispersion and oscillator energies as well as es. Oppositely, el values increased from 12.52 to 24.45 as a result of larger grain size and less defect density associated with annealing process when T-a is raised from 200 to 400 degrees C, respectively. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 22Citation - Scopus: 23Temperature Effects on the Structural and Optical Properties of the Tlinse2xs2(1-x)< Mixed Crystals (x=0.3)(Elsevier Science Sa, 2017) Omar, A.; Qasrawi, A. F.; Gasanly, N. M.In this work, we have studied the temperature effects on the recrystallization process and on the energy band gap of the TlInSe(2)xS(2(1 - x)) mixed crystals at the critical composition (x = 0.3) where structural phase transition from tetragonal to monoclinic takes place. Remarkable effect which included permanent recrystallization process, enlargements in the monoclinic crystallite size, decreases in the compressing strain and in the dislocation density as well as in the stacking faults and in the energy band gap with increasing temperature were observed. In addition, the temperature dependent energy band gap of the crystal which is investigated in the same temperature range that was used for the recrystallization process revealed that the recrystallization process is associated with energy band gap narrowing. (C) 2017 Elsevier B.V. All rights reserved.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: 7Citation - Scopus: 7Interband Critical Points in Tlgax< Layered Mixed Crystals (0 ≤ x ≤ 1)(Elsevier Science Sa, 2013) Isik, M.; Işık, Mehmet; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringThe layered semiconducting TlGaxIn1-xS2 mixed crystals (0 <= x <= 1) were studied by spectroscopic ellipsometry measurements in the 1.2-6.2 eV spectral range at room temperature. The spectral dependence of the components of the complex dielectric function, refractive index and extinction coefficient were revealed using an optical model. The interband transition energies in the studied samples were found from the analysis of the second-energy derivative spectra of the complex dielectric function. The variation of the obtained energies with composition were plotted to see the effect of the substitution of indium with gallium. Moreover, a simple diagram showing the revealed transitions in the available electronic band structure was given for TlGaS2 single crystals. (C) 2013 Elsevier B.V. All rights
