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Öğe Amorphous WO3 thin films designed as gigahertz/terahertz dielectric lenses(Springer Link, 2022) Qasrawi, Atef Fayez; Abu Alrub, Shatha N.; Daragme, Rana B.Herein, tungsten oxide thin films comprising excess oxygen are treated as optical resonator suitable for gigahertz/terahertz applications. WO3 thin films which are prepared by the thermal evaporation technique under a vacuum pressure of 10? 5 mbar are structurally, compositionally and optically evaluated. The amorphous WO3 films which showed high transparency permit electronic transitions within an indirect allowed energy band gap of 3.05 eV. The band gap comprised energy band tails of width of 190 meV. Four dominant dielectric resonators centered in the infrared (IR), visible (VIS) and ultraviolet (UV) ranges of light are detected. Analysis of the optical conductivity in accordance with the Drude-Lorentz approaches have shown that the drift mobility of free holes in this amorphous layer can be as large as 5.61 cm2/Vs an as low as 1.59 cm2/Vs when exposed to IR and UV light signals, respectively. In addition, the gigahertz/terahertz cutoff frequency (fco) spectra demonstrated fco values in the gigahertz frequency domain when exposed to IR light. Excitations with light signals in the VIS and UV spectral ranges allow fco values that extends from 0.7 to 40.0 THz. The wide range of tunability of the WO3 dielectric resonators nominates them as dielectric lenses suitable for optical communications.Öğe Design and characterization of (Yb, Al, Cu, Au)/GeO2/C As MOS field effect transistors, negative capacitance effect devices and band pass/reject filters suitable for 4G technologiet(Springer Link, 2022) Qasrawi, Atef Fayez; Daragme, Rana B.Herein, the efect of Yb, Al, Cu and Au metal substrates on the electrical performance of germanium oxide-based devices is reported. Back-to-back Schottky-type metal-insulator-metal (MIM) electronic devices with the structure (Yb, Al, Cu, Au)/ GeO2/C are prepared by vacuum evaporation under a vacuum pressure of 10?5 mbar. Capacitance-voltage characteristic curve analysis on these devices have shown that, while the forward-biased Al/GeO2/C displays NMOS (enhanced N-channel metal oxide semiconductor) characteristics, Cu/GeO2/C and Au/GeO2/C show inverted NMOS and PMOS felds efect transistor (FET) characteristics under forward and reverse biasing conditions, respectively. A large scale (8–737 nm) of depletion width and built-in potentials engineering is possible via metallic substrate selection. In addition, current-voltage characteristic curve analysis have shown that the dominant transport mechanism is by electric feld-assisted tunneling through narrow barriers. The only device that showed current rectifcation was the Yb/GeO2/C device. The absence of the recertifcation property from the (Al, Cu, Au)/GeO2/C devices is assigned to the large surface roughness of the metal substrates. Analysis of the capacitance, conductance, impedance and refection coefcient spectra in the frequency domain of 0.01–1.80 GHz have shown that the proposed device structures can exhibit features of negative capacitance efect devices and tunable microwave/ radio wave cavities. The observed notch frequency values of the (Yb, Al, Cu, Au)/GeO2/C devices make them suitable for use as bandpass/reject flters suitable for 4G technologyÖğe Effects of Amorphous Si Substrates on the Optoelectronic Properties of Zinc Phthalocyanine Thin Films(Springer, 2024) Qasrawi, Atef Fayez; Daragme, Rana B.In the current work the effect of amorphous silicon (a-Si) substrates on the structural, optical and electrical properties of zinc phthalocyanine (ZnPc) thin films is explored. ZnPc thin films are coated onto glass and a-Si substrates by the thermal evaporation technique under a vacuum pressure of 10–5 mbar. It is observed that a-Si substrates lead to a lattice expansion, increased strain, increased stacking faults percentages and increased defect densities. Coating ZnPc films onto a-Si substrates reduced the crystallite sizes from 28 to 24 nm and decreased the energy band gap from 3.20 eV to 2.50 eV. In addition the temperature dependent electrical resistivity measurements has shown that deeper acceptor levels are formed in the energy band gap of ZnPc. Although the room temperature electrical resistivity increased by 45.5% upon coating the films onto a-Si, the light absorption in ZnPc increased by more than 24 times at 2.65 eV. The enhanced light absorption together with the shift in the energy band gap indicates that a-Si makes ZnPc films more adequate for optoelectronic applications.Öğe Fabrication and characterization of Se/WO3 heterojunctions designed as terahertz/gigahertz dielectric resonators(Elsevier, 2022) Qasrawi, Atef Fayez; Daragme, Rana B.In this work, Selenium (Se) thin film substrates are coated with tungsten oxide thin layers. The Se/WO3 interfaces are fabricated using a vacuum deposition technique. The substrates displayed stable polycrystalline structure of hexagonal selenium when coated with amorphous WO3. The surface morphology revealed preferred growth of Se nanowires. The coating of Se with WO3 enhanced the light absorbability in the visible and infrared ranges of light spectrum. In addition, the Se/WO3 heterojunctions exhibited conduction and valence band offsets of values of 2.03 eV and 0.63 eV, respectively. The band offsets are sufficiently large to force quantum confinement at the interface. It was observed that Se/WO3 behaves as good dielectric resonator revealing resonance peaks in the infrared, visible and ultraviolet ranges of light. Moreover, computing the optical conductivity parameters for these dielectric oscillators revealed drift mobility and plasmon frequency values that are suitable for optical communications. Furthermore, as a terahertz resonator, the Se/WO3 dielectric media displayed terahertz cutoff frequency values in the range of 0.6-75 THz depending on the exciting photon energy. As practical application, when photo-excited with daylight light, the carbon contacted planner Se/WO3 interfaces displayed a light power dependent photosensitivity. The photosensitivity increases 38 times upon irradiation of 0.9 W. With these features, the Se/WO3 heterojunction devices can be nominated for applications in optical communications.Öğe Transparent In/SeO2 thin film transistors designed for gigahertz/terahertz technologies(Springer Link, 2022) Qasrawi, Atef Fayez; Daragme, Rana B.Herein, thin films of selenium oxide are coated onto transparent indium substrates with thickness of 150 nm under vacuum pressure of 10–5 mbar. In/SeO2 optical receivers are structurally, optically and electrically characterized. Induced crystallization of tetragonal SeO2 showing homogeneous composition and continuous film formation is achieved via indium substrates. Indium thin films enhance the light absorbability and optical conductivity without altering the energy band gap of SeO2. Strong interaction between In and Se at the ultrathin interface of In/SeO2 led to the formation of a new second band gap of 0.92 eV relating to direct allowed transitions in InSe. Indium substrates increased the dielectric constant of SeO2 by more than four times, making SeO2 suitable for nonlinear optical applications. The terahertz cutoff frequency changed in the range of 0.9–14.0 THz. In-depth analysis of the optical conduction in In/SeO2 films showed that the films display drift mobility, plasmon frequency and free carrier density values that render In/SeO2 a suitable candidate for fabrication of thin film transistors. The transistors displayed microwave resonator features presented by double band stop filters. The filters showed return loss values larger than 20 dB and voltage standing wave ratios of 1.0 at 1.16 GHz. A negative capacitance effect is also observed for the transistors under study.Öğe YB/SE/WO3/YB thin film transistors as rectifiers, 2 n-channel metal oxide semiconductor capacitors, 3 laser sensors, and microwave bandstop filters(Wiley, 2022) Qasrawi, Atef Fayez; Daragme, Rana B.Herein, Yb/p–Se/p–WO3/Yb heterojunctions are employed as multifunctional 6 devices. The devices which show back-to-back Schottky (BBS) diode character 7 istics are prepared by the thermal evaporation method under a vacuum pressure 8 of 10 5 mbar. The structural and morphological analyses on these heterojunc 9 tions have shown the growth of amorphous WO3 onto meshed nano/microwire 10 network of hexagonal selenium. The BBS diodes display voltage-controlled 11 current rectification ratios. In addition, the domination of the thermionic and 12 tunneling current conduction mechanisms in the transistors is computationally 13 investigated. Moreover, studies of the capacitance–voltage characteristic curves 14 demonstrate the performance of the devices as n-channel metal oxide semi 15 conductor (NMOS) field-effect transistors responsive in the frequency domain of 16 1.0–50.0 MHz. Furthermore, the impedance spectroscopy measurements in the 17 frequency domain of 0.01–1.80 GHz indicate the possibility of using the BBS 18 diodes as bandstop filters. The microwave cutoff frequency of these filters 19 reaches 1.06 GHz. On the other hand, when ohmic contacts are formed on the 20 glass/Se/WO3 part using two carbon electrodes, the active layer between the 21 electrodes displays high sensitivity to light irradiations from He–Ne lasers, 22 indicating the possibility of performing as photosensors.Öğe Yb/WO3/Yb back to back Schottky barriers designed as voltage controlled rectifiers and as microwave resonators(Forum of Chalcogeniders, 2022) Qasrawi, Atef Fayez; Daragme, Rana B.Herein, p ?WO3 thin films coated onto ytterbium thin film substrates are used as active layers to fabricate a back to back Schottky (BBS) barriers. The Schottky contacts and the tungsten oxide active layers are grown by the thermal evaporation technique under a vacuum pressure of 10-5 mbar. The films are structurally, morphologically, optically and electrically characterized. The physical nature of the grown p ?WO3 layers is amorphous comprising excess oxygen in its composition. Electrically, the BBS devices displayed a biasing dependent current rectification ratio confirming the tunneling type of Schottky barriers. The current conduction are dominated through tunneling barriers of height of ~0.80 eV. The barriers allow hole tunneling within energy barriers of widths of ~45 nm and of 300 nm under reverse and forward biasing conditions, respectively. In addition, the impedance spectroscopy measurements have shown the ability of wide tunability of the resistance and capacitance of the devices resulting in a microwave cutoff frequency exceeding 2.0 GHz. The resistive and capacitive features of the devices in addition to the microwave cutoff frequency spectra nominate the Yb/p-WO3/Yb BBS devices for use as microwave resonators suitable for 4G/5G technologies.Öğe Yb/WO3/Yb back to back Schottky barriers designed as voltage controlled rectifiers and as microwave resonators(S.C. Virtual Company of Phisics S.R.L, 2022) Qasrawi, Atef Fayez; Daragme, Rana B.; Qasrawi, Atef FayezHerein, p -WO3 thin films coated onto ytterbium thin film substrates are used as active layers to fabricate a back to back Schottky (BBS) barriers. The Schottky contacts and the tungsten oxide active layers are grown by the thermal evaporation technique under a vacuum pressure of 10-5 mbar. The films are structurally, morphologically, optically and electrically characterized. The physical nature of the grown p -WO3 layers is amorphous comprising excess oxygen in its composition. Electrically, the BBS devices displayed a biasing dependent current rectification ratio confirming the tunneling type of Schottky barriers. The current conduction are dominated through tunneling barriers of height of ~0.80 eV. The barriers allow hole tunneling within energy barriers of widths of ~45 nm and of 300 nm under reverse and forward biasing conditions, respectively. In addition, the impedance spectroscopy measurements have shown the ability of wide tunability of the resistance and capacitance of the devices resulting in a microwave cutoff frequency exceeding 2.0 GHz. The resistive and capacitive features of the devices in addition to the microwave cutoff frequency spectra nominate the Yb/p-WO3/Yb BBS devices for use as microwave resonators suitable for 4G/5G technologies. © 2022, S.C. Virtual Company of Phisics S.R.L. All rights reserved.Öğe ZnPc based multifunctional devices designed as fast capacitors, rectifiers, infrared detectors and microwave resonators adequate for 6 G technology applications(Iop Publishing Ltd, 2024) Qasrawi, A. F.; Daragme, Rana B.Herein Zinc phthalocyanine (ZnPc) based multifunctional devices are fabricated and characterized. The device fabrication included formation of an Au nanosheets onto n-Si wafers and coating these nanosheets with 500 nm thick ZnPc layer. Silver and platinum were used to form a Schottky and an ohmic contacts with n-Si and ZnPc, respectively. The device hybrid structure (Ag/n-Si/Au/p-ZnPc/Pt; abbreviated as ASZ) is composed of Ag/n-Si Schottky arm and p- and n- layers forming pn junction separated by Au nanosheets. Electrical and photoelectrical measurements on the ASZ devices have shown their ability to perform as conventional metal-oxide-semiconductor capacitors (CMOS). These CMOS devices showed light and frequency controlled charge accumulation, depletion and inversion mechanisms within the range of 1.0-50 MHz. The flat band and threshold voltages of the ASZ capacitors are engineered by the imposed ac signal frequency and by infrared (IR) light. In addition, ASZ devices performed as biasing controlled IR photosensors and as current rectifiers. A rectification ratio of 103, IR light sensitivity of 39, specific detectivity of .96 x 10 9 Jones and current responsivity exceeding 9.0 mA W-1 are recorded at biasing voltage of 4.5 V. Moreover ASZ devices displayed microwave resonator characteristics presented by negative capacitance effect, resonance -antiresonance phenomena and high microwave cutoff frequency. The latter is larger than 10 GHz nominating the device for 6 G technology applications.
