Effect of ionic substitution on the structural, dielectric nd electrical properties of bismuth zinc niobate ceramics

A.F. Qasrawi 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.4

The effects of tin substitution on the structural, dielectric and electrical properties of the Bi1.5Zn0.92Nb1.5O6.92 pyrochlore ceramics have been investigated. Tin atoms was substituted in the A (Bi1.5Zn0.46 )-site instead of zinc and in the B ((Zn0.46Nb1.5) -site instead of niobium in accordance to the chemical formulae Bi1.5Zn0.92Nb1.5-xSnxO6.92-x/2 and (Bi1.5-x/3Zn0.46-3x/ 2Snx)(Nb1.5Zn0.46)O6.92, for 0.00 ≤ x ≤ 0.40 and 0.00 ≤ x ≤ 0.60, respectively. A relative single phase formation of the structures was possible for x values less than 0.25 and less than 0.10. Pronounced tunability in the dielectric constant values associated with very low dielectric loss are obtainable by Sn substitution. Furthermore, a frequency invariant but linearly varying temperature dependent dielectric constant is observed. The electrical conductivity decreased by two and one order of magnitude for the A and B-site substitutions, respectively. The temperature-dependent conductivity analysis in the temperature region of 300-500 K, reflected the existence of shallow and deep impurity energy levels being created by the doping process.

Properties of Tl4Se3S single crystals and characterization of Ag/Tl4Se3S Schottky barrier diodes

A.F. Qasrawi,N.M. Gasanly 한국물리학회 2010 Current Applied Physics Vol.10 No.2

The main physical properties of Tl4Se3S single crystals were investigated for the first time. Particularly,the crystal data, Debye temperature, dark electrical resistivity and Hall effect in addition to the temperature dependent current–voltage characteristics and photosensitivity of the Ag/Tl4Se3S Schottky barrier diode were studied. The X-ray diffraction patterns have revealed that the crystal exhibited a single phase of tetragonal structure belonging to the D184h - I4mcm space group. A Debye temperature of 100 K was calculated using the results of the X-ray diffraction analysis. The dark electrical resistivity and Hall-effect measurements indicated that the samples exhibits p-type conduction with an electrical resistivity, carrier concentration and Hall mobility of 6.20 × 103 Ωcm, 1.16 × 1012 cm-3 and 873 ㎠ V-1 s-1, respectively. The crystals were observed to have Schottky diode properties. The Ag/Tl4Se3S Schottky barrier device bias voltage was observed to depend on the crystal direction and on temperature. It was found that the calculated energy barrier height decreased and the diode ideality factor increased with temperature decreasing. The photosensitivity–light intensity dependence of this device was found to be linear reflecting the ability of using it in optoelectronics.

Gold and ytterbium interfacing effects on the properties of the CdSe/Yb/CdSe nanosandwiched structures

S.R. Alharbi,A.F. Qasrawi 한국물리학회 2018 Current Applied Physics Vol.18 No.8

Owing to the performance of the CdSe as an optoelectronic material used for the production of quantum dots, photosensors and wave traps we here, in this article, report the enhancements in structural and electrical properties that arises from the nanosandwiching of a 40 nm thick Yb film between two films of CdSe (CYbC-40). The CdSe films which were deposited onto glass, Yb and Au substrates are characterized by X-ray diffraction, temperature dependent electrical conductivity and impedance spectroscopy measurements in the frequency range of 10–1800 MHz. The analysis of the XRD patterns have shown that the glass/CdSe/Yb/CdSe films exhibit larger grain size and lower strain, defect density and lower stacking faults compared to the not sandwiched CdSe. In addition, it was observed that the Yb shifts the donor states of the n-type CdSe from 0.44 to 0.29 eV leading to a modification in the built in voltage of the material. On the other hand, the design of the energy band diagram has shown the ability of the formation of the Au/CYbC-40/Yb as Schottky (SB) and the Au/CYbC-40/Au as back to back Schottky barriers (BBSB). While the SB device show low band pass filter characteristics, the BBSB device performed as band stop filters. The BBSB device exhibited negative capacitance effects with filtering features that reveal a return loss of 42 dB at ∼1440 MHz.

Band offsets and optical conduction in the CdSe/GaSe interface

T.S. Kayed,A.F. Qasrawi,Khaled A. Elsayed 한국물리학회 2016 Current Applied Physics Vol.16 No.7

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 1018 (cm3). The field effect mobility for the CdSe/GaSe interface was found to be 5.22 (cm2/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.

Fabrication and characterization of Yb/MoO3/(C,Yb) devices

S.E. Al Garni,A.F. Qasrawi 한국물리학회 2019 Current Applied Physics Vol.19 No.4

In this study we have explored some of the properties of Yb/MoO3/(C, Yb) thin films as a multifunctional optoelectronic device. While the MoO3 films which are deposited onto glass substrate are found to be of amorphous nature, the Yb metal induced the growth of orthorhombic phase of MoO3. The films are high transparent and exhibit energy band gap value of 3.0 eV which make it sensitive to light signals in the near ultraviolet range of light. In addition, the frequency dependent capacitance-voltage characteristics of Yb/MoO3/ (C,Yb) structure display pronounced accumulation, depletion and inversion regions that nominate it for use as tunable metal-oxide-semiconductor MOS device. The physical parameters including the built in voltage, barrier height, flat band and threshold voltages of the MOS capacitors are also determined. Furthermore, the currentvoltage characteristics displayed high rectification ratio that could reach 1.26×104 at biasing voltage of 0.5 V nominating the Yb/MoO3/C device for use as electronic switches. On the other hand, the impedance spectroscopy analysis in the frequency domain of 0.01–1.80 GHz, have shown that the Yb/MoO3/Yb structures are more appropriate for microwave applications than Yb/MoO3/C device. The microwave cutoff frequency for the Yb sandwiched MoO3 exceeds 140 GHz. The return loss for the Yb/MoO3/Yb reaches 26 dB at 1.8 GHz. These values are attractive as they suit microwave low/high pass band filters.

Characterization of Au/As2Se3/MoO3/Ag hybrid devices designed for dual optoelectronic applications

T.S. Kayed,A.F. Qasrawi 한국물리학회 2020 Current Applied Physics Vol.20 No.1

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.

Effect of ytterbium, gold and aluminum transparent metallic substrates on the performance of the Ga2S3 thin film devices

S.R. Alharbi,A.F. Qasrawi 한국물리학회 2017 Current Applied Physics Vol.17 No.6

In the current work, the structural, optical, dielectric and electrical properties of the Ga2S3 thin films which are deposited onto transparent thin Al, Yb and Au metal substrates are characterized by means of transmittance electron microscopy, X-ray diffraction, ultravioletevisible light spectroscopy and impedance spectroscopy techniques. The effects of the metallic substrates on the crystalline nature, energy band gap and dielectric spectra are also investigated. The modeling of the dielectric spectra allowed determining the effect of the Al, Yb and Au thin layers on the electron scattering time, the plasmon frequency, free electron density and drift mobility. In addition, a Yb/Ga2S3/Au Schottky barrier and Al/ Ga2S3/Au back to back Schottky barrier devices (metal-semiconductor-metal (MSM) device) are fabricated and characterized by means of capacitance -voltage characteristics and capacitance and conductance spectra in the frequency range of 10e1800 MHz. While the Schottky barrier device displayed three distinct positions of resonance-antiresonance phenomena, the MSM device displayed one peak with narrow bandwidth of 10 MHz. The MSM devices exhibited an inversion, depletion and accumulation modes within a voltage range of 0.25 V width at 250 MHz. The study indicates the applicability of these device as smart capacitive switches, as Plasmon devices and as wavetraps.

Design and performance of Yb/ZnS/C Schottky barriers

Najla M. Khusayfan,S.E. Al Garni,A.F. Qasrawi 한국물리학회 2017 Current Applied Physics Vol.17 No.1

In this work, ZnS thin films are deposited onto glass and transparent ytterbium substrates under vacuum pressure of 105 mbar. The effects of the Yb substrate on the structural, mechanical, optical, dielectric and electrical performance of the ZnS are explored by means of the energy dispersion X-ray analyzer, X-ray diffraction, UVeVIS spectroscopy, current-voltage characteristics and impedance spectroscopy techniques. The techniques allowed determining the lattice parameters, the grain size, the degree of orientation, the microstrain, the dislocation density, the optical and the excitonic gaps, the energy band offsets and the dielectric resonance and dispersion. The (111) oriented planes of glass/ZnS and Yb/ZnS exhibited 2.06% lattice mismatch between Yb and ZnS and degree of orientation values of 63% and 51.6%, respectively. The interfacing of the ZnS with Yb shrunk the energy band gap of ZnS by 0.50 eV. On the other hand, the electrical analysis on the Yb/ZnS/C Schottky device has revealed a rectification ratio of 3.48 104 at a biasing voltage of 0.30 V. The barrier height and ideality factor was also determined. Moreover, the impedance spectroscopy analysis have shown that the Yb/ZnS/C device is very attractive for use as varactor devices of wide tunability. The device could also be employed as microwave resonator above 1337 MHz.