Browsing by Author "Omareya, Olfat A."

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Citation - WoS: 6
Citation - Scopus: 6
Characterization of the A1/Ge/In₂Se₃/Ga₂S₃/Al hybrid tunneling barriers designed for Gigahertz/Terahertz applications
(Elsevier Science Sa, 2018) Qasrawi, A. F.; Omareya, Olfat A.
In the current work, we report the design and performance of a tunneling amorphous thin film hybrid device made of Ge/In2Se3/Ga2S3 sandwiched between two aluminum thin films. Each of the stacked semiconducting layers are of 200 nm thicknesses. The hybrid device which is composed of a p-n junction between two Schottky shoulders is designed to have two valence band offsets of 0.59 and 0.84 eV at the Ge/In2Se3 and at In2Se3/Ga2S3 interfaces, respectively The offsets which caused two quantum confinements forces the device to exhibit field effect assisted thermionic and thermionic transport mechanisms under the reverse and forward biasing conditions, respectively. When an alternating current signal is imposed between the terminals of the device, the device conducted by the quantum mechanical tunneling of charge carriers and by the correlated barrier hopping above and below 0.180 GHz, respectively. The hybrid structure are also observed to exhibit series and parallel resonance at the switching frequency between the two conduction mechanisms. It also exhibited negative differential capacitance effect in the frequency domain of 0.18-1.80 GHz. For the Al/Ge/In(2)Se3/Ga2S3/Al hybrid structure the microwave cutoff frequency reached 100 GHz. The latter value is promising as it indicates the ability of using the device as fast switches and microwave/Tera wave traps.
Citation - WoS: 11
Citation - Scopus: 12
Effect of Au Nanosandwiching on the Structural, Optical and Dielectric Properties of the as Grown and Annealed Inse Thin Films
(Elsevier Science Bv, 2017) Omareya, Olfat A.; Qasrawi, A. F.; Al Garni, S. E.
In the current work, the structural, optical and dielectric properties of the InSe/Au/InSe nanosandwiched structures are investigated by means of X-ray diffraction and UV-visible light spectrophotometry techniques. The insertion of a 20 and 100 nm thick Au metal slabs between two InSe layers did not alter the amorphous nature of the as grown InSe films but decreased the energy band gap and the free carrier density. It also increased; the absorption ratio and the values of dielectric constant by similar to 3 times. The insertion of 100 nm Au layers as a nanosandwich enhanced the drift mobility (31.3 cm(2)/V s) and plasmon frequency (1.53 GHz) of the InSe films. On the other hand, upon annealing, a metal induced crystallization process is observed for the InSe/Au (100 nm)/InSe sandwiches. Particularly, while the samples sandwiched with a layer of 20 nm thickness hardly revealed hexagonal gamma -In2Se3 when annealed at 300 degrees C, those sandwiched with 100 nm Au slab, displayed well crystalline phase of hexagonal gamma -In2Se3 at annealing temperature of 200 degrees C. The further annealing at 300 degrees C, forced the appearing of the orthorhombic In4Se3 phase. Optically, the annealing of the InSe/Au(100 nm)/InSe at 200 degrees C improved the absorption ratio by similar to 9 times and decreased the energy band gap. The nanosandwiching technique of InSe seems to be promising for the engineering of the optical properties of the InSe photovoltaic material.
Citation - WoS: 11
Citation - Scopus: 11
Formation and Characterization of Cd₂s_{3< Polycrystalline Films Onto Glass and Lanthanum Substrates}
(Springer, 2019) Qasrawi, A. F.; Omareya, Olfat A.
In this article, the structural, optical and dielectric properties of the rarely investigated Cd2S3 thin films are reported. Particularly, Cd2S3 thin films prepared by the thermal evaporation technique onto glass, and 150-nm-thick lanthanum transparent substrate studied by means of energy-dispersive structural analysis have shown that the Cd2S3 thin films are of polycrystalline nature. The hexagonal unit cell parameters, which slightly differ from that of CdS, increased upon replacement of glass with lanthanum. All the other structural parameters including the grain size, strain and defect density are accordingly affected. While the optical band gap increased when La replaces glass, the high-frequency dielectric constant decreased. On the other hand, the Drude-Lorentz modeling of the dielectric spectra has shown that the La/Cd2S3 thin films are promising materials for production of thin film transistors as they exhibit drift mobility values of approximate to 13.3cm(2)/Vs. The response of the glass/Cd2S3 and La/Cd2S3 interfaces to the incident electromagnetic light is associated with hole-plasmon interactions that are limited by plasmon frequency values in the range of 0.4-8.1GHz. Such property makes this material attractive as microwave band pass/reject filters.
Citation - WoS: 4
Citation - Scopus: 4
In situ observations of the permanent structural modifications, phase transformations and band gap narrowing upon heating of Cu₂Se/Yb/Cu₂Se films
(Elsevier Science Sa, 2019) Qasrawi, A. F.; Omareya, Olfat A.
In this study, we have investigated the temperature dependent structural, optical and dielectric properties of Cu2Se thin films that are nanosandwiched with 50 nm thick ytterbium slab (CYC). The X-ray diffraction monitoring of the films during the heating process in the temperature range of 293-473 K has shown that the CYC films which contain both of the cubic and orthorhombic phases in its structure exhibits lattice expansion that increases the grain size and decreases the defect density, stacking faults and microstrain by 12.5% and by 28.9%, 12.8% and 11.3%, respectively. The CYC films show enhanced permanent crystallinity presented by high degree of orientation with reduction of the weight of the orthorhombic phase after cooling. On the other hand, a red shift in the energy band gap value is observed during the heating process. The analysis of the temperature dependent optical properties has shown a good correlation between the lattice expansion and energy band gap narrowing. In additions, the CYC samples are observed to exhibit negative capacitance effect that nominates the material for use in electronic circuits. The negativity of the capacitance decreased with increasing temperature due to the reduction in the defect density. (C) 2019 Elsevier B.V. All rights reserved.