Browsing by Author "Kayed, T. S."

Now showing 1 - 9 of 9

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.
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.
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: 3
Citation - Scopus: 3
Characterization of As₂se_{3< Heterojunction Designed for Multifunctional Operations}
(Iop Publishing Ltd, 2021) Qasrawi, A. F.; Kayed, T. S.
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.
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: 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
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: 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.
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
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 - 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: 5
Citation - Scopus: 6
Structural, Optical, Dielectric and Electrical Properties of Al-Doped Znse Thin Films
(Springer, 2019) Kayed, T. S.; Qasrawi, A. F.; Elsayed, Khaled A.
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.