Browsing by Author "Shehada, Sufyan R."

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Citation Count: 2
Dielectric and Optoelectronic Properties of Inse/Cds Heterojunctions
(Springer, 2018) Abusaa, M.; Qasrawı, Atef Fayez Hasan; Qasrawi, A. F.; Shehada, Sufyan R.; Department of Electrical & Electronics Engineering
The effect of an InSe substrate on the structural, optical and dielectric properties of CdS/CdSe heterojunctions prepared by physical vapor deposition technique under vacuum pressure of 10(-8) bar are reported. The structural analysis carried out by x-ray diffraction revealed a strained type of growth of the CdS/CdSe heterojunction onto the InSe along the axis of the hexagonal lattice. The lattice mismatches and strained nature of the heterojunctions associated with the InSe participation causes a quantum confinement that results in a red shift in the energy band gap, enhanced near infrared (IR) light absorbability, and valence band offsets of 0.62eV and 0.53eV for the InSe/CdS and CdS/CdSe interfaces, respectively. In addition, a pronounced enhancement in the real part of the dielectric constant by 2.5 times is observed at 1.25eV. Furthermore, the Durde-Lorentz modeling of the optical conductivity of the CdS/CdSe and InSe/CdS/CdSe reveals significant increases in the drift mobility values from 43.8cm(2)/Vs at the CdS/CdSe interface to 100.0cm(2/)Vs upon replacement of glass by an amorphous InSe substrate. The other optical conduction parameters including the free carrier scattering time at the femtosecond level, the plasmon frequency and the free carrier density are also improved accordingly. The photocurrent illumination intensity dependence for the studied system showed that the presence of InSe increases the photocurrent values and changes the recombination mechanism from sublinear at the surface to trap-assisted recombination. The smart feature of the InSe/CdS/CdSe system is that the structurally controlled quantum confinement results in having mobile photocarriers arising from the enhanced absorbability and large dielectric response in the IR region.
Citation Count: 8
Dielectric dispersion in InSe/CdS bilayers
(Elsevier Science Bv, 2018) Qasrawı, Atef Fayez Hasan; Shehada, Sufyan R.; Department of Electrical & Electronics Engineering
In the current study, the effect of the amorphous InSe thin film substrate on the structural, optical and dielectric properties of CdS are investigated. The structural analysis of the bilayers indicated a strained growth of CdS onto InSe leading to decrease in grain size and increase in the dislocation density. The optical measurements have shown that the InSe/CdS exhibits two direct allowed transitions energy band gap values of 2.04 and 1.38 eV, in the high and low absorption regions, respectively. On the other hand, the detailed analysis of the dielectric spectra for the InSe, CdS and InSe/CdS layers has shown that the presence of the InSe substrate significantly improves the optical conduction parameters. Particularly, the Drude-Lorentz modeling for these dielectric systems revealed a drift mobility value of 329 cm(2)/V for the InSe/CdS bilayer. The deposition of the CdS onto InSe is also observed to shift the plasmon frequency of CdS from 2.49 to 0.77 GHz. The general features of the InSe/ CdS as plasmon cavities are promising as it shows its usability for production of optoelectronic devices that exhibit high performance at very high frequencies.
Citation Count: 7
Negative Capacitance Effect in Ag/-in_{2< Dual Band Stop Filters}
(Springer, 2019) Khanfar, Hazem K.; Qasrawı, Atef Fayez Hasan; Qasrawi, A. F.; Shehada, Sufyan R.; Department of Electrical & Electronics Engineering
In the current study, a 1.5m thick three channel microwave band filter is designed and characterized. The thin film device which was constructed from the indium selenide, cadmium sulfide and cadmium selenide stacked dielectric materials sandwiched between silver and carbon films is studied by means of x-ray diffraction, energy dispersive x-ray analysis and impedance spectroscopy techniques. It was observed that the Ag thin film substrate induced the formation of the hexagonal -In2Se3 phase of indium selenide. The x-ray analysis has also shown that the deposition of hexagonal CdS over Ag/-In2Se3 and that of hexagonal CdSe over -In2Se3/CdS under vacuum pressure of 10(-8) bar is of a highly strained and mismatched physical nature. The impedance spectroscopy analysis in the frequency domain of 0.10-1.80GHz has shown that; while the Ag/-In2Se3/C channel exhibit negative capacitance (NC) effects in the frequency domain of 0.10-1.40GHz, the Ag/-In2Se3/CdS/C and the Ag/-In2Se3/CdS/CdSe/C channels displayed a NC feature in the domains of 1.24-1.40GHz and 1.10-1.56GHz, respectively. The fitting of the capacitance spectra in accordance with the modified Ershov model allowed determining the NC and band filtering parameters. It was also observed that, although the Ag/-In2Se3/C channel behaves as a high frequency low pass filter, the second and third channels displayed band stop filter features with notch frequencies of 1.38GHz and 1.49GHz, respectively. The features of the device nominate it for use as a parasitic capacitance canceller and as a three channels microwave filter.