Browsing by Author "Kayed, Tarek Said"

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Citation - WoS: 6
Citation - Scopus: 6
Al/Cdse Resonant Tunneling Thin Film Transistors
(Elsevier Science Bv, 2017) Qasrawi, A. F.; Kayed, T. S.; Elsayed, Khaled A.; Department of Electrical & Electronics Engineering
An Al/CdSe/GaSe/C thin film transistor device was prepared by the physical vapor deposition technique at a vacuum pressure of 10(-5) mbar. The x-ray diffraction measurements demonstrated the polycrystalline nature of the surface of the device. The de current-voltage characteristics recorded for the Al/CdSe/C and Al/CdSe/GaSe/C channels displayed a resonant tunneling diode features during the forward and reverse voltage biasing, respectively. In addition, the switching current ratio of the Al/CdSe/C increased from 18.6 to 9.62x10(3) as a result of the GaSe deposition on the CdSe surface. Moreover, the alternating electrical signal analyses in the frequency range of 1.0 MHz to 1.8 GHz, showed some remarkable properties of negative resistance and negative capacitance spectra of the AVCdSe/GaSe/C thin film transistors. Two distinct resonance-antiresonance phenomena in the resistance spectra and one in the capacitance spectra were observed at 0.53, 1.04 and 1.40 GHz for the Al/CdSe/C channel, respectively. The respective resonating peak positions of the resistance spectra shift to 0.38 and 0.95 GHz when GaSe is interfaced with CdSe. These features of the thin film transistors are promising for use in high quality microwave filtering circuits and also for use as ultrafast switches.
Citation - WoS: 4
Citation - Scopus: 4
Band Offsets and Optical Conduction in the Cdse/Gase Interface
(Elsevier Science Bv, 2016) Kayed, T. S.; Qasrawi, A. F.; Elsayed, Khaled A.; Department of Electrical & Electronics Engineering
In this work, the design and characterization of CdSe/GaSe heterojunction is considered. The CdSe/GaSe thin film interface was prepared by the physical vapor deposition technique. Systematic structural and optical analysis were performed to explore the crystalline nature, the optical band gaps, the conduction and valence band offsets, the dielectric spectra, and the frequency dependent optical conductivity at terahertz frequencies. The X-ray diffraction analysis revealed a polycrystalline interface that is mostly dominated by the hexagonal CdSe oriented in the (002) direction. It was also found that the CdSe/GaSe interface exhibits conduction and valence band offsets of 1.35 and 1.23/1.14 eV, respectively. The dielectric spectra displayed two dielectric resonance peaks at 530 and 445 THz. Moreover, the computational fittings of the optical conductivity of the interface revealed a free carrier scattering time of 0.41 (fs) for a free carrier density of 7.0 x 10(18) (cm(-3)). The field effect mobility for the CdSe/GaSe interface was found to be 5.22 (cm(2)/Vs). The remarkable features of this device having large band offsets and qualitative optical conduction dominated by a scattering time in the order of femtoseconds in addition to the dielectric property nominate the device to be used in optoelectronic technology. (C) 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Characterization of As₂se_{3< Heterojunction Designed for Multifunctional Operations}
(Iop Publishing Ltd, 2021) Qasrawi, A. F.; Kayed, T. S.; Department of Electrical & Electronics Engineering
In this article, As2Se3/MoO3 heterojunction devices are structurally, compositionally, optically and electrically characterized. The heterojunction devices which are prepared by the thermal evaporation technique under vacuum pressure of 10(-5) mbar are observed to exhibit amorphous nature of growth. The optical spectrophotometry measurements and analyses on the heterojunction devices revealed a conduction and valence band offsets of values of 2.64 and 4.08 eV, respectively. In addition, the dielectric dispersion and the optical conductivity parametric analyses have shown that the heterojunction could exhibit large drift mobility value up to 73.7 cm(2) V-1 s(-1). From electrical point of view, while the capacitance- voltage curves reveal characteristics of MOSFET devices, the current--voltage curves display tunneling diode characteristics. The features of the As2Se3/MoO3 devices including the band offsets, drift mobility, plasmon frequency, microwave band filtering and MOSFET characteristics make them attractive for use as thin films transistors suitable electrical and optical applications.
Citation - WoS: 11
Citation - Scopus: 12
Characterization of Au/As_{2< Hybrid Devices Designed for Dual Optoelectronic Applications}
(Elsevier, 2020) Kayed, T. S.; Qasrawi, A. F.; Department of Electrical & Electronics Engineering
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.
Citation - WoS: 9
Citation - Scopus: 11
Effect of Lithium Doping on the Properties of Tl-Based Superconductors
(Iop Publishing Ltd, 2001) Kayed, TS; Özkan, H; Gasanly, NM; Department of Electrical & Electronics Engineering
The effects of lithium doping on the formation and properties of the T1-based superconductors have been studied. Lithium atoms up to around 3 mol.% have been added to the oxides of nominal composition Tl1.8Ba2Ca2.2Cu3Ox, and the usual solid-state reaction method has been applied. Lithium additions in the range 0.23-0.29 mol.% increase the fraction of the Tl-2223 phase and significantly improve the critical temperature of the samples. Higher amounts of lithium additions diminish the Tl-2223 phase, reduce the fraction of the Tl-2212 phase, and cause separate non-superconducting phases to be formed.
Citation - WoS: 3
Citation - Scopus: 3
Effect of Magnetic Field and Γ Irradiation on the Properties of Tl-2212 Superconducting Tape
(Wiley-v C H verlag Gmbh, 2002) Kayed, TS; Ercan, I; Mathematics; Department of Electrical & Electronics Engineering
The critical temperature and critical current of Tl-2212 superconducting sample in the form of a tape have been studied near T-c under magnetic field and gamma irradiation. T-c decreases from 109 to 94 K with increase of magnetic field up to 300 mT. In 77-109 K range, J(c) decreases rapidly in low fields up to around 50 mT followed by a very slow decrease in J(c) up to 300 mT. T-c of the sample did not change up to 100 MR gamma dose and then started to decrease from 109 to 102 K with increase of gamma dose up to 800 MR, most of the change taking place in high doses. The critical currents of the sample decreased steadily with gamma irradiation up to 600 MR after which no further change was noticed.
Citation - WoS: 5
Citation - Scopus: 5
Electrical Behavior of Pb_1.83mg_{0.29< Pyrochlore Ceramics}
(Elsevier Science Bv, 2004) Mergen, A; Kayed, TS; Department of Electrical & Electronics Engineering
Pb1.83Mg0.29Nb1.71O6.39 pyrochlore was produced via a simple partial oxalate method. It was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Single phase, belonging to the cubic pyrochlore structure, with a lattice parameter of a = 10.60125 +/- 0.001 Angstrom and grain size that varies from 5 to 10 mum was obtained. The electrical properties were measured at different temperatures in the range 15-320 K without and with applied magnetic field of 1.4 T. Current-voltage characteristics data were fitted to a power law expression V=I-beta(T) in which the exponential parameter beta takes values around 1 at all temperatures except at 300 K. Resistance starts from 3.3 x 10(10) Omega at 15 K and increases gradually to 4.8 x 10(10) Omega at 240 K. It drops to approximately 1.2 x 10(10) Omega at 300 K, after which it increases again to around 1.6 x 10(10) Omega at 320 K. (C) 2004 Elsevier B.V. All rights reserved.
Citation - WoS: 9
Citation - Scopus: 9
Electrical Properties of Bi_1.5znsb_{1.5< Pyrochlore Ceramics}
(Wiley-v C H verlag Gmbh, 2003) Kayed, TS; Mergen, A; Department of Electrical & Electronics Engineering
Bi1.5ZnSb1.5O7 pyrochlore samples were prepared by solid state reaction method. They were examined by x-ray diffraction and scanning electron microscopy. Single phase, belongs to the cubic pyrochlore structure, with a lattice parameter of 10.442 Angstrom and grain size that varies from 16 to 20 mum was obtained. The electrical properties were measured at different temperatures in the range 15-330 K under different applied magnetic fields up 1.4 T. In our measurements for Hall coefficient, Hall resistivity, and mobility; we noticed an anomalous behavior at two temperatures (around 250 and 310 K) which was supported by the I-V measurements (double transition of the slope of I-V characteristics (beta) at the same temperatures). This was discussed in terms of polarization phenomenon and mixed ionic-electronic conduction. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Citation - WoS: 25
Citation - Scopus: 25
Fabrication and Some Physical Properties of Agin₅s_{8< Thin Films}
(Elsevier Science Sa, 2004) Qasrawi, AF; Kayed, TS; Ercan, I; Department of Electrical & Electronics Engineering; Mathematics
AgIn5S8 thin films are deposited on glass substrates, kept at 300 K, by thermal evaporation of AgIn5S8 single crystals under the pressure of 10-5 Torr. The X-ray fluorescence analysis revealed that the films have a weight percentage of similar to11.5% Ag, 61.17% In, and 27.33% S which corresponds to 1:5:8 stoichiometric composition. X-ray analysis of the films reveals the polycrystalline nature of the films. The lattice parameter (a) of the films was calculated to be 10.784(5) Angstrom. The dark n-type electrical conductivity of the films was measured in the temperature range of 30-350 K. The conductivity data analysis shows that the thermionic emission of the charge carriers having activation energies of 147 and 224 meV in the temperature ranges of 130-230 and 240-350 K, respectively, are the dominant transport mechanism in the films. The variable range hopping transport mechanism is dominant below 130 K. The room temperature photocurrent-photon energy dependency predicts a band gap of 1.91 eV of the films. The illumination intensity-photocurrent dependency measured in the intensity range of 13-235 W cm(-2) reveals monomolecular recombination (linear) in the films and bimolecular recombination (sublinear) at the film surface corresponding to low and high applied illumination intensities, respectively. The time-dependant photocurrent measured at fixed illumination intensity reveals a response time of 0.85, 2.66 and 10.0 s in the time periods of 0-0.5, 0.5-1.0, and 1.0-10.0 s, respectively. (C) 2004 Elsevier B.V. All rights reserved.
Citation - WoS: 18
Citation - Scopus: 18
Heat Treatment Effects on the Structural and Electrical Properties of Thermally Deposited Agin₅s_{8< Thin Films}
(Pergamon-elsevier Science Ltd, 2011) Qasrawi, A. F.; Kayed, T. S.; Ercan, Filiz; Department of Electrical & Electronics Engineering
The heat treatment effects on structural and electrical properties of thermally deposited AgIn5S8 thin films have been investigated. By increasing the annealing temperature of the sample from 450 to 500 K, we observed a change in the crystallization direction from (420) to (311). Further annealing of the AgIn5S8 films at 550, 600 and 650 K resulted in larger grain size in the (311) preferred direction. The room temperature electrical resistivity, Hall coefficient and Hall mobility were significantly influenced by higher annealing temperatures. Three impurity levels at 230, 150, and 78 meV were detected for samples annealed at 350 K. The electrical resistivity decreased by four orders of magnitude when the sample annealing temperature was raised from 350 to 450 K. The temperature dependent electrical resistivity and carrier concentration of the thin film samples were studied in the temperature ranges of 25-300 K and 140-300 K, respectively. A degenerate-nondegenerate semiconductor transition at approximately 180 was observed for samples annealed at 450 and 500 K. Similar type of transition was observed at 240 K for samples annealed at 600 and 650 K. (C) 2011 Elsevier Ltd. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 4
Magnetoresistance, Voltage-Current Characteristics, and Hall Effect Measurements of Bulk Mgb₂ Superconductors
(Wiley-v C H verlag Gmbh, 2004) Kayed, TS; Department of Electrical & Electronics Engineering
Bulk MgB2 samples were prepared from the commercially available powder (Alfa-Aesar). One of the samples was used in measuring the transport properties by the DC four-probe technique while the other was used in measuring Hall effect using the van-der-Pauw configuration. From the transport measurements, we noticed that the R-T curves shift to lower temperatures under applied magnetic field without any observed enlargement of the transition width. T-c gradually decreases from 37 K at zero field to 32 K at B = 1.4 T. Our V-I data were found to obey a power law expression V proportional to I-beta(T,I- B). The change of beta with temperature and magnetic field was shown and discussed. R-H is positive under positive applied magnetic field. The 1/R-H linear dependency on T, usually observed in high temperature superconductors, could not be observed in our case. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Citation - WoS: 11
Citation - Scopus: 11
Microstructural, thermal, and electrical properties of Bi_1.7V_0.3Sr₂Ca₂Ca₃O_x glass-ceramic superconductor
(Wiley-v C H verlag Gmbh, 2004) Kayed, TS; Calinli, N; Aksu, E; Koralay, H; Günen, A; Ercan, I; Cavdar, S; Mathematics; Department of Electrical & Electronics Engineering
A glass-ceramic Bi1.7V0.3Sr2Ca2Cu3Ox superconductor was prepared by the melt-quenching method. The compound was characterized by scanning electron microscopy, x-ray diffraction, differential thermal analysis, current-voltage characteristics, transport resistance measurements, and Hall effect measurements. Two main phases (BSCCO 2212 and 2223) were observed in the x-ray data and the values of the lattice parameters quite agree with the known values for 2212 and 2223 phases. The glass transition temperature was found to be 426 degreesC while the activation energy for crystallization of glass has been found to be E-a = 370.5 kJ / mol. This result indicates that the substitution of vanadium increased the activation energy for the BSCCO system. An offset T-c of 80 K was measured and the onset T-c was 100 K. The Hall resistivity rho(H) was found to be almost field-independent at the normal state. A negative Hall coefficient was observed and no sign reversal of rho(H) or RH could be noticed. The mobility and carrier density at different temperatures in the range 140-300 K under different applied magnetic fields up to 1.4 T were also measured and the results are discussed.
Citation - WoS: 4
Citation - Scopus: 4
Optical Characterization of the Mgo/Inse Interface
(Wiley-v C H verlag Gmbh, 2015) Kayed, T. S.; Qasrawi, A. F.; Elsayed, Khaled A.; Department of Electrical & Electronics Engineering
In this work, a 500nm thick MgO layer deposited on the physically evaporated amorphous InSe thin film substrate is designed as a window for the MgO/InSe terahertz resonators. The optical properties including the reflectance and the dielectric constant dependence on the angle of incidence ((i)), the normal transmittance, and the absorption coefficient of the interface were investigated in the range of approximate to 270-1000THz. It was observed that the total reflectivity of the substrate continuously decreases with increasing (i) in the range of 33-80 degrees. The spectra of InSe and MgO/InSe revealed strong dielectric resonance patterns below 450THz. The energy bands of the direct allowed transitions in InSe film shrunk from 3.90, 2.75, and 1.49eV to 3.71, 2.10, and 0.96eV when MgO was deposited onto the InSe film. By analyzing the dielectric spectra, we were able to determine the static and lattice dielectric constants in addition to the oscillator and dispersion energies. The latter energy increased from 27.43 to 35.84 via interface construction.
Citation - WoS: 7
Citation - Scopus: 7
Photoconductivity Kinetics in Agin₅s_{8< Thin Films}
(Elsevier Science Sa, 2010) Qasrawi, A. F.; Kayed, T. S.; Ercan, Ismail; Department of Electrical & Electronics Engineering
The temperature (T) and illumination intensity (F) effects on the photoconductivity of as grown and heat-treated AgIn5S8 thin films has been investigated. At fixed illumination intensity, in the temperature region of 40-300K, the photocurrent (I-ph) of the films was observed to decrease with decreasing temperature. The I-ph of the as grown sample behaved abnormally in the temperature region of 170-180K. At fixed temperature and variable illumination intensity, the photocurrent of the as grown sample exhibited linear, sublinear and supralinear recombination mechanisms at 300 K and in the regions of 160-260K and 25-130 K. respectively. This behavior is attributed to the exchange of role between the linear recombination at the surface near room temperature and trapping centers in the film which become dominant as temperature decreases. Annealing the sample at 350 K for 1 h improved the characteristic curves of I-ph. The abnormality disappeared and the I-ph - T dependence is systematic. The data analysis of which revealed two recombination centers located at 66 and 16 meV. In addition, the sublinear recombination mechanism disappeared and the heat-treated films exhibited supralinear recombination in most of the studied temperature range. (C) 2010 Elsevier B.V. All rights reserved.
Citation - Scopus: 12
Production of Anorthite From Kaolinite and Caco3 Via Colemanite
(Trans Tech Publications Ltd, 2004) Mergen,A.; Kayed,T.S.; Bilen,M.; Qasrawi,A.F.; Gürü,M.; Department of Electrical & Electronics Engineering
Boron oxide has been found to be useful flux for the preparation of dense anorthite ceramics (CaO.Al2O3.2SiO2). Inexpensive starting materials of kaolinite, calcium carbonate and silica were used for anorthite ceramic production. Colemanite (2CaO.3B2O 3.5H2O) was added into the mixtures and the effects of colemanite upon the transformation towards anorthite and on the densification were investigated between 900-1400°C. Single phase anorthite ceramic formed at lower temperatures in boron containing mixtures. Boron containing powder compacts were sintered above 90% theoretical density at 1350°C.
Citation - WoS: 10
Production of Anorthite From Kaolinite and Caco₃ Via Colemanite
(Trans Tech Publications Ltd, 2004) Mergen, A; Kayed, TS; Bilen, M; Qasrawi, AF; Gürü, M; Department of Electrical & Electronics Engineering
Boron oxide has been found to be useful flux for the preparation of dense anorthite ceramics (CaO.Al2O3.2SiO(2)). Inexpensive starting materials of kaolinite, calcium carbonate and silica were used for anorthite ceramic production. Colemanite (2CaO.3B(2)O(3).5H(2)O) was added into the mixtures and the effects of colemanite upon the transformation towards anorthite and on the densification were investigated between 900-1400 degreesC. Single phase anorthite ceramic formed at lower temperatures in boron containing mixtures. Boron containing powder compacts were sintered above 90% theoretical density at 1350 degreesC.
Citation - WoS: 7
Citation - Scopus: 9
Properties of Boron Doped Ti-Ba Superconductors
(Pergamon-elsevier Science Ltd, 2003) Kayed, TS; Department of Electrical & Electronics Engineering
The effects of boron doping on the formation and properties of the Tl-based superconductors have been studied. Up to 10 wt.% boron has been added to the oxides having the nominal composition, Tl1.8Ba2Ca2.2Cu3Ox, by the usual solid-state reaction method. Boron additions in the range 0.8-1.0% increase the fraction of the Tl-2223 phase and significantly improve the critical temperature of the samples. Higher amounts of boron additions eliminate the Tl-2223 phase, reduce the fraction of Tl-2212 phase and cause separate non-superconducting phases to be formed. The formation of non-superconducting phases does not allow us to obtain pure Tl-2212 phase. (C) 2002 Elsevier Science Ltd. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 4
Properties of Se/Inse Thin-Film Interface
(Springer, 2016) Qasrawi, A. F.; Qasrawı, Atef Fayez Hasan; Kayed, T. S.; Elsayed, Khaled A.; Kayed, Tarek Said; Qasrawı, Atef Fayez Hasan; Kayed, Tarek Said; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics Engineering
Se, InSe, and Se/InSe thin films have been prepared by the physical vapor deposition technique at pressure of similar to 10(-5) torr. The structural, optical, and electrical properties of the films and Se/InSe interface were investigated by means of x-ray diffraction (XRD) analysis, ultraviolet-visible spectroscopy, and current-voltage (I-V) characteristics. XRD analysis indicated that the prepared InSe films were amorphous while the Se films were polycrystalline having hexagonal structure with unit cell parameters of a = 4.3544 and c = 4.9494 . Spectral reflectance and transmittance analysis showed that both Se and InSe films exhibited indirect allowed transitions with energy bandgaps of 1.92 eV and 1.34 eV, respectively. The Se/InSe interface exhibited two energy bandgaps of 0.98 eV and 1.73 eV above and below 2.2 eV, respectively. Dielectric constant values were also calculated from reflectance spectra for the three layers in the frequency range of 500 THz to 272 THz. The dielectric constant exhibited a promising feature suggesting use of the Se/InSe interface as an optical resonator. Moreover, the Au/Se/InSe/Ag heterojunction showed some rectifying properties that could be used in standard optoelectronic devices. The ideality factor and height of the energy barrier to charge carrier motion in this device were found to be 1.72 and 0.66 eV, respectively.
Citation - WoS: 1
Citation - Scopus: 1
Pseudodielectric Dispersion in As₂se_{3< Thin Films}
(Wiley-v C H verlag Gmbh, 2020) Kayed, Tarek S.; Kayed, Tarek Said; Qasrawi, Atef F.; Qasrawı, Atef Fayez Hasan; Kayed, Tarek Said; Qasrawı, Atef Fayez Hasan; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics Engineering
Herein, X-ray diffraction, energy dispersive X-ray spectroscopy, and spectral ellipsometry techniques are used to investigate the structural, pseudo-optical, and pseudodielectric properties of arsenic selenide thin films. The stoichiometric films which are prepared by the thermal evaporation technique are found to prefer the amorphous nature of growth. While the pseudoabsorption coefficient spectra display strong absorption bands at 1.84, 1.81, 1.41, and 1.13 eV, the preferred pseudo-optical transitions happen within a direct forbidden energy bandgap of 1.80 eV. In addition, the real part of the pseudodielectric spectra displays three strong resonance peaks at critical energy values of 2.33, 1.90, and 1.29 eV. Modeling of the imaginary part of the pseudodielectric constant spectra in accordance with the Drude-Lorentz approach results in the existence of six linear oscillators. The response of arsenic selenide to elliptically polarized light signals shows that the films exhibit drift mobility, free electron concentration, and plasmon frequency values in the ranges of 0.21-43.96 cm(2) V(-1)s(-1), 1.90-58.0 x 10(19) cm(-3), and 5.8-32.0 GHz, respectively. The optical conductivity parameters for As2Se3 film nominate it as a promising candidate for the fabrication of tunneling diodes suitable for microwaves filtering up to 32.0 GHz and as thin-film transistors.
Citation - WoS: 4
Citation - Scopus: 5
Structural, Optical, Dielectric and Electrical Properties of Al-Doped Znse Thin Films
(Springer, 2019) Kayed, T. S.; Qasrawi, A. F.; Elsayed, Khaled A.; Department of Electrical & Electronics Engineering
In this work, the heavy aluminum doping effects on the compositional, structural, optical, dielectric and electrical properties of ZnSe thin films are investigated. It is observed that the Zn/Se compositional ratio increases with increasing Al content. The major cubic phase of ZnSe becomes more pronounced compared to the hexagonal phase. In addition, the presence of Al in the structure of ZnSe causes lattice constant contraction, decreased the grain size and increased both of the strain and defect density. Optically, the Al doping increased the light absorbability and widens both of the energy band gap and energy interbands which are present in the band gap of ZnSe films. Moreover, the Al doping into ZnSe lowers the high frequency dielectric constant and enhances the optical conductivity. On the other hand, the capacitance spectra which are studied in the frequency domain of 0.01-1.80GHz displayed negative capacitance effect associated with resonance-antiresonance phenomena upon doping of ZnSe with Al. Such enhancements in the physical properties of ZnSe that are achieved via Al doping make the zinc selenide thin films more appropriate for electronic and optoelectronic technological applications.