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Optical properties of chromium-selenide films designed for terahertz applications
(Optik, Eylul 2023) Aljaloud, Amjad Salamah M.; Qasrawi, Atef Fayez; Alfhaid, Latifah Hamad Khalid
Herein the effects of indium substrates on the properties of chromium selenide thin films are reported. Chromium selenide thin films and indium substrates are prepared by the thermal evaporation technique under a vacuum pressure of 10?5 mbar. It is observed that indium sublayers alters the atomic stoichiometry of chromium selenide. It induces the formation of Cr2Se3 phase instead of CrSe2 phase which grow onto glass substrates. Both of the glass/CrSe2 and In/Cr2Se3 films displayed direct and indirect energy band gaps. The respective gaps are 2.60 eV and 3.19 eV and 2.25 eV and 2.83 eV. The Urbach tails states exhibited a width of 2.24 eV in glass/CrSe2 and showed value of 0.85 eV in In/Cr2Se3. In addition a light absorbability enhancement of more than 45% is reached at the In/Cr2Se3 interfaces in the visible range of light. Moreover, as terahertz resonators, In/Cr2Se3 films showed larger optical conductivity. It also displayed a spectral terahertz cutoff frequency in the range of 3.0–35 THz. Furthermore, when utilized as terahertz resonators, In/Cr2Se3 films demonstrate heightened optical conductivity and a spectral terahertz cutoff frequency ranging from 3.0 to 35 THz. Analyzing these terahertz oscillators using Drude-Lorentz models reveals that the density of free charge carriers increases with higher oscillator energy, while the drift mobility of these carriers within the terahertz resonators varies between 1.10 and 3.09 cm²/Vs. The array of features showcased by In/Cr2Se3 thin films, including their performance as terahertz resonators, positions them as strong contenders for applications in optical and terahertz technologies.
Performance of Pt/CRSe schottky diodes designed for 5G/6G technology applications
(Virtual Co. Physics SRL, 2024) Alfhaid, Latifah Hamad Khalid; Qasrawi, Atef Fayez
Herein thin films of CrSe deposited by the thermal evaporation technique onto Pt substrates are designed as Schottky diodes. It is observed that the Pt/CrSe/C (PCC) Schottky diodes are of tunneling type showing barrier height and widths of 0.56 eV and 18 nm, respectively. These diodes displayed biasing dependent nonlinearity and negative slope of differential resistance. The analyses of the cutoff frequency spectra indicated that PCC devices can exhibit high cutoff frequency up to 17 GHz based on the driving signal frequency. The features of the PCC devices make it promising as electronic component suitable for 5G/6G technology applications.
Growth of Polycrystalline n? CrSe2 Nanosheets Onto p –Si Substrates and their Applications as Rectifiers and Gigahertz Band Filters
(Springer, 2024) Algarni, Sabah E.; Qasrawi, Atef Fayez; Khusayfan, Najla M.
a vacuum evaporation technique under a vacuum pressure of 10– 5 mbar. Experimental and theoretical structural investigations have shown the preferred growth of trigonal CrSe2. The unit cell parameters being a = b = 3.520 Å,c = 5.889 Å and P3m1(164) fits well with the standards of trigonal CrSe2 structure. Nanosheets of chromium selenide displayed low defect density of the order of 1010 lines/cm2 along the a? and b axes. Surface morphology studies have shown that CrSe2 nanosheets is composed of spherical grains of average sizes of 200 nm. Optically the interfacing of the n– type CrSe2 nanosheets with p? type Si results in formation of a conduction and valence band offsets of 0.95 eV and 0.47 eV, respectively. These band offsets were found sufficient to allow running the Si/CrSe2 interfaces as pn junction devices. The devices displayed a biasing dependent rectification ratios (asymmetry). The ratios which reached value of 70 can be varied with the applied voltage. Deep analyses of the current transport mechanism of these rectifiers have shown the domination by thermionic and tunneling mechanisms under forward and reverse biasing conditions, respectively. Moreover the pn junction device showed features of band filters with cutoff frequency values suiting gigahertz technology making the device attractive for multifunction operations.
InSe/CrSe interfaces performed as resistive switches and band filters for Gigahertz/Terahertz communication technology applications
(Springer, 2024) Algarni, Sabah E.; Qasrawi, Atef Fayez; Khusayfan, Najla M.
Herein chromium selenide (n-CrSe) nanosheets are deposited onto amorphous indium selenide (n-InSe) thin films by the thermal evaporation technique under a vacuum pressure of 10?5 mbar. The formed InSe/CrSe heterojunctions are structurally, optically and electrically investigated. InSe/CrSe heterojunctions exhibited a band structure discontinuities at the InSe/CrSe interfaces presented by a conduction and valence band offsets of 0.50 eV and 0.65 eV, respectively. The isotype InSe/CrSe heterojunctions exhibited resistive switching property under a forward and reverse biasing voltages of 1.5 V and 0.3 V, respectively. In addition computer assisted fittings which were carried out on the current–voltage characteristics of the InSe/CrSe devices have shown the existence of large barrier height of 1.75 eV at the InSe/CrSe interfaces. Moreover, low amplitude ac signal analyses have shown that the device under study performed as negative conductance sources with increased negative conductance values with increasing signal frequency. The negative conductance effect resulted from the deficiency of selenium atoms in InSe and CrSe as confirmed by the energy dispersive X-ray spectroscopy. Furthermore combination of the analysis of the picofarad level- capacitance with the conductance allowed determining the cutoff limits of the InSe/CrSe devices when treated as signal filters. The cutoff frequency of the InSe/ CrSe devices varied in the range of 10M-1.1 THz assuring the suitability of the devices for megahertz/gigahertz/terahertz technology applications
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.
Pb/FeSe interfaces designed for optical communication technology
(Wiley, 2023) Alharbi, Seham R.; Qasrawi, Atef Fayez; Algarni, Sabah E.
Herein, thin films of FeSe are coated onto glass and semitransparent Pb substrate of thicknesses of 200 nm. The produced glass/FeSe (GFS) and Pb/FeSe (PFS) are structurally, compositionally, and optically characterized. It is observed that Pb substrates induced the crystallinity of cubic FeSe and cubic PbSe. On average, 21% of the phases in FeSe films are identified as PbSe. Due to the strong orbital overlapping between Pb and FeSe, Pb substrate increases the light absorption, the dielectric constant, the optical conductivity, and the terahertz cutoff frequency by ?150 %, 180 %, 263 %, and 101 %, respectively. In addition the direct and indirect energy bandgaps shrink from 2.49 and 2.80 to 2.41 and 2.50 eV, respectively. Moreover, treating GFS and PFS as terahertz optical resonators have shown that Pb substrates enhanced the drift mobility and increased the plasmon frequency making it adequate for 6G technology applications. An important feature of the PFS optical resonator is the stability of the terahertz cutoff frequency at 16 THz in the visible range of light. This feature together with the enhanced optical absorption in the visible light region makes the PFS films attractive for visible light communication technology.
Fast crystallization of InSe thin films via pulsed laser welding technique and effect of crystallinity on the optical and dielectric properties
(IOP Publishing, 2024) Khusayfan, Najla M.; Qasrawi, Atef Fayez; Khanfar, Hazem K.; Alharbi, Seham R.
Physica Scripta Inclusive Publishing Trusted Science, find out more. ACCEPTED MANUSCRIPT Fast crystallization of InSe thin films via pulsed laser welding technique and effect of crystallinity on the optical and dielectric properties Najla M. Khusayfan1, A F Qasrawi2, Hazem Khanfar3 and Seham Alharbi4 Accepted Manuscript online 18 January 2024 • © 2024 IOP Publishing Ltd What is an Accepted Manuscript? DOI 10.1088/1402-4896/ad2040 DownloadAccepted Manuscript PDF Download PDF Article metrics 3 Total downloads Submit Submit to this Journal MathJax Turn on MathJax Permissions Get permission to re-use this article Share this article Share this content via email Share on Facebook (opens new window) Share on Twitter (opens new window) Share on Mendeley (opens new window) Hide article and author information Author e-mails atef.qasrawi@aaup.edu Author affiliations 1 Department of Physics, University of Jeddah, Jeddah, Jeddah, Makkah, 21959 , SAUDI ARABIA 2 Physics Department, Arab American University, Telfit,, Jenin, P298, Palestine, State of 3 Computer system Engineering , Arab American University, Telfit,, Jenin, Jenin, P298, Palestine, State of 4 Physics Department, University of Jeddah, jeddah, Jeddah, Makkah, 21959 , SAUDI ARABIA ORCID iDs A F Qasrawi https://orcid.org/0000-0001-8193-6975 Hazem Khanfar https://orcid.org/0000-0002-3015-4049 Dates Received 5 October 2023 Revised 17 December 2023 Accepted 18 January 2024 Accepted Manuscript online 18 January 2024 Journal RSS Sign up for new issue notifications Abstract In the current study the crystalline phase of indium selenide thin films which were grown by the thermal evaporation technique is achieved via pulsed laser welding technique (PLW) in a second. The films crystallinity is achieved under various welding conditions including the pulse width (PW), repetition frequency (f_r ) and pulse diameter (d). The optimum parameters for obtaining well crystalline phase are PW=1.0 ms, f_r=10Hz and d=1.0 mm. PLW induced crystallinity showed preferred structure relating to monoclinic phase of InSe. Compositionally while amorphous films exhibited In2Se3 chemical structure, crystalline ones preferred InSe phase. Associated with this type of crystallinity, direct and indirect energy band gap values of 2.32 eV and 3.12 eV are determined. The crystalline films showed lower dielectric constant value accompanied with higher optical conductivity and higher terahertz cutoff frequency in the infrared range of light. In addition the dielectric dispersion spectra were treated using Drude-Lorentz model to read the optical conductivity parameters for the PLW assisted crystalline InSe terahertz resonators. The treatment showed that the crystallinity of the films resulted in improved free carrier density, longer relaxation times at femtosecond level, larger plasmon frequencies and higher drift mobility values. These features together with the response of terahertz cutoff frequency to IR excitations make crystalline InSe thin films promising for optoelectronic and terahertz technology applications.
Growth and characterization of chromium selenide thin films for optoelectronic applications
(Optical and Quantum Electronics, 2023) Aljaloud, Amjad Salamah M.; Qasrawi, Atef Fayez; Alfhaid, Latifah Hamad Khalid
Herein amorphous and stoichiometric CrSe2 thin films are obtained by the thermal deposition (TD) technique under a vacuum pressure of 10?5 mbar. The films are structurally, morphologically, optically and dielectrically characterized. It is observed that CrSe2 thin films grown by TD technique exhibit optical excitations within direct and indirect allowed energy band gaps of 2.60 eV and 3.19 eV, respectively. The amorphous CrSe2 thin films contained a wide range of exponential band distribution presented by Urbach energy width of 2.24 eV. In addition in contrast to the chemical bath deposition technique which produced Cr7Se8 films of low dielectric constant ( ), the TD technique revealed high dielectric constant values up to 11.9 for CrSe2 films. Moreover, the Drude-Lorentz modeling of the imaginary part of the dielectric constant spectra revealed drift mobility values in the range of 0.70–6.45 cm2/Vs. The plasmon frequency varied in the range of 5.42–8.33 GHz. Furthermore, analysis of the terahertz cutoff frequency ( ) spectra have shown that CrSe2 thin films exhibit values in the range of 3.30–40.0 THz. The features of CrSe2 thin films deposited by the thermal evaporation technique are promising semiconductor layers suitable for 6G and terahertz technology applications.
Effects of Pb nanosheets substrates on the optical and electrical properties CrSe thin films
(Physica Scripta, 2023) Aljaloud, Amjad Salamah M.; Qasrawi, Atef Fayez; Alfhaid, Latifah Hamad Khalid
Herein the effects of lead nanosheets substrates on the optical and electrical properties of chromium selenide thin films were studied. Chromium selenide thin films were grown by vacuum thermal evaporation technique onto glass and 100 nmthick lead nanosheets substrates. The effects of Pb nanosheets on the structural, morphological, compositional, optical and electrical properties was explored. While films grown onto glass substrates showed compositional stoichiometry forming CrSe2 phase those coated onto Pb substrates preferred the growth CrSe phase. Both films were of amorphous structure and exhibited direct and indirect allowed optical transitions. Pb nanosheets enhanced the optical absorption of chromium selenide in the visible and ultraviolet ranges of light. Formation of films onto Pb nanosheets resulted in band gaps and band tails narrowing and decreased the room temperature electrical conductivity (s) as well. Deep analyses of the s - T variations in the range of 25–340 Kshowed that the electronic transport is dominated by the thermal excitation and variable range hopping of charge carriers. It was observed that Pb nanosheets increased the average hopping energy and hopping range, decreased the density of localized states near the Fermi level and increased the degree of state disorder. The features of glass/CrSe2 and Pb/CrSe films are promising for using then in optoelectronic technology
Copper doping effects on the optical and dielectric properties of amorphous indium selenide thin films
(Springer, 2023) Qasrawi, Atef Fayez; Aboalrub, Fatima M.
(a-InSe) thin films were doped with copper using the thermal evaporation technique under a vacuum pressure of 10– 5 mbar. The aim was to investigate the impact of Cu doping on the optical absorption, energy band gap, dielectric dispersion, optical conduction, and terahertz cutoff frequency. Notably, Cu doping levels of 1.41 at.% and 2.97 at.% in a-InSe resulted in a significant enhancement in light absorption by more than three and four times, respectively, without significantly altering the energy band gap. Furthermore, Cu doping led to a remarkable increase in the dielectric constant value and caused a redshift in the position of the dielectric resonance peak. Moreover, a noticeable enhancement in the optical conductivity and terahertz cutoff frequency values was observed in a-InSe films doped with 2.97 at.% of Cu. The Drude-Lorentz fittings of the optical conductivity data demonstrated that the presence of Cu atoms increased the scattering time at the femtosecond level and enhanced the drift mobility from ~ 5.0 cm2/ Vs for undoped films to ~ 113 cm2/ Vs for 2.97 at.% Cu-doped films. Additionally, the range of the terahertz cutoff limit expanded, covering a range of 0.1–16 THz. The study indicate that the features exhibited by Cu-doped InSe hold promise for various optoelectronic applications including terahertz technology
Iron selenide nanowire bundles for microwave communication technology
(Wiley, 2023) Toubasi, Ahmad J.; Qasrawi, Atef Fayez
Herein stacked layers of FeSe2 deposited onto ytterbium substrates using the thermal evaporation technique under a vacuum pressure of 10-5 mbar are observed to form nanowire bundles (NB). Structural investigations on these NBs have shown the preferred growth of orthorhombic FeSe2 in addition to hexagonal ytterbium selenide as a minor phase in the structure of FeSe2. Impedance spectroscopy analyses conducted in the frequency domain of 0.01-1.80 GHz shown that FeSe2 stacks can exhibit a negative capacitance effect and band stop filter characteristics. For these band stop filters, the refection coefficient (S11), the voltage standing wave ratios (VSWR) and the return loss (Lr) spectra displayed optimum values at a notch frequency of 0.87 GHz. In addition, computational analysis using Lorentz Oscillator (LO) Model has shown that the negativity of the capacitance is dominated by two oscillators centered at 0.08 GHz and 1.25 GHz. On the other hand, the insertion of aluminum nanosheets between the stacked layers of FeSe2 has been observed to decrease the negativity of the capacitance, increase the values of S11 and Lr and bring the VSWR closer to ideality. FeSe2 nanowire bundles resulting from FeSe2 stacks comprising Al nanosheets are considered suitable for microwave communication technology.
Synthesis of copper nanosheets coatings onto glass and glass/CrSe2 substrates using ion coating technique for terahertz technology
(Wiley, 2023) Alfhaid, Latifah Hamad Khalid; Qasrawi, Atef Fayez
In this study, copper (Cu) nanosheets are utilized as semitransparent conducting optical windows for the fabrication of terahertz band filters based on chromium selenide (CrSe2). The deposition of CrSe2 thin films onto glass substrates is performed via the thermal evaporation technique followed by the application of Cu nanosheets using the ion coating technique. The interaction between Cu windows and CrSe2 films resulted in a slight widening of the energy bandgap and a remarkable reduction in the Urbach tail states from 2.24 to 1.23 eV. Furthermore, the coating of CrSe2 with Cu optical windows led to a decrease in the dielectric constant values of more than 35% and an increase in the terahertz cutoff frequency by more than 70%. The application of Cu windows increased the cutoff frequency to 23 THz. The correlation between electrical and optical conduction in the terahertz band filters is investigated through the utilization of Drude–Lorentz models, revealing that although Cu windows reduced the free carrier density and conductivity, they enhanced drift mobility, resulting in more efficient terahertz filter properties. The calculated optical constants and optical conductivity parameters provided evidence of the suitability of Cu-coated CrSe2 films for applications in terahertz technology.
Au/CrSe stacked layers designed as optical absorbers, tunneling barriers and negative capacitance sources
(Elsevier, 2023) Alfhaid, Latifah Hamad Khalid; Qasrawi, Atef Fayez
Herein thin films of CrSe (500 nm) are deposited onto glass and semitransparent gold nanosheets (100 nm) under a vacuum pressure of 10?5 mbar. Au nanosheets substrates induced the formation of CrSe instead of CrSe2 which grows onto glass substrates. The Au/CrSe stacked layers exhibited enhanced light absorption reaching 25% in the ultraviolet, visible and infrared ranges of light. In addition Au nanosheets successfully redshifted the direct allowed transitions energy band gap from 2.60 eV to 2.40 eV. On the other hand electrical investigations have shown that CrSe2 thin films exhibit a work function of 5.064 eV. The Au/CrSe interfaces displayed tunneling type Schottky barriers of height of 0.56 eV and barrier width of 8 nm. When an ac signal was imposed between the terminals of the Au/CrSe Schottky barriers a negative capacitance (NC) effects was observed in the spectral range of 0.02–1.80 GHz. The NC reached value of ? 100 pF at 0.32 GHz. Fitting of the ac conductivity assuming tunneling type of transport indicated a high degree of localization near the Fermi level reaching a density of cm?3 eV?1. The enhanced light absorption and moderate value of work function in addition to the tunneling type of Schottky formation performing as NC source make the Au/CrSe interfaces promising for use in the design of electro-optic system.
Electrical properties of amorphous Cu doped InSe thin films
(Springer, 2023) Qasrawi, Atef Fayez; Abuarra, Maryam Khalefa N.
In this study, we employed thermal evaporation under vacuum conditions to introduce copper dopants into amorphous InSe thin films. Our objective was to scrutinize the effects of varied copper doping concentrations on the structural, compositional, electrical, and photoelectrical properties of the films. Our observations indicated that copper doping did not induce discernible alterations in the amorphous morphology of the InSe films, yet it yielded notable enhancements in the material’s atomic stoichiometry. Notably, films subjected to both pristine conditions and 0.09 at. % copper doping exhibited extrinsic n-type conductivity behavior, while those doped with 0.42 at. % copper displayed a transition to p-type conductivity. Furthermore, our investigation encompassed electrical conductivity measurements conducted over a temperature range spanning from 100 to 320 K, elucidating the dominance of thermal excitation mechanisms at higher temperatures, and the prevalence of variable range hopping (VRH) processes at lower temperatures. The magnitude of copper dopants in the InSe matrix exerted discernible influence over impurity kinetics and VRH parameters, encompassing factors such as the degree of disorder, density of states proximate to the Fermi level, and average hopping distance. Additionally, our photoelectrical assessments unveiled that a nominal concentration of copper doping (0.09 at. %) yielded a remarkable augmentation of over 70% in the photoconductivity of the InSe films, underscoring its potential suitability for optoelectronic applications.
Optically controlled n ?Si/p ?SeO2/p ?SiO2 microwave resonators designed for 5G/6G communication technology
(Physica Scripta, 2023) Qasrawi, Atef Fayez
Herein n?Si/p?SiO2 interfaces comprising layers of p-SeO2 are employed as an optically controllable microwave resonators. The stacked layers of SeO2 (500 nm) and SiO2 (50 nm) were deposited onto n- type Si thin crystals by the thermal evaporation technique under a vacuum pressure of 10?5 mbar. Ytterbium and Au metals were coated onto SiO2 and Si layers, respectively, to form Schottky arms. Energy band diagram analyses were performed to confirm the formation of doubled conduction and valence band offsets. These offsets create energy barriers and potential wells that contribute to the bistable behavior. Photo-impedance spectroscopic measurements were conducted on the device under blue light, demonstrating its ability to function as a light-power tunable microwave resonator andMOScapacitor. In the absence of light, negative capacitance (NC) effects were observed above a driving frequency of 1.07 GHz. As the device was exposed to light and the light power increased, the frequency range ofNCeffects shifted to higher driving frequencies. Furthermore, the range ofNC effects became narrower with increasing light power, indicating a more limited frequency range for the manifestation of negative capacitance. In addition, n- Si/ p- SeO2/ p- SiO2 microwaves resonators displayed high cutoff frequency exceeding 0.10 THz at driving frequency of 1.07 GHz in the dark. The driving frequency also shifted toward larger values as light power is increased indicating the ability to optically control the cutoff frequency range and value. The high response of the capacitance, conductance, cutoff frequency spectra and the dependence of capacitance–voltage characteristics on incident light power nominate the device as microwave resonators andMOS electro-optic devices suitable for 5G/6G communication technology.
LaGe2 thin films designed as band filters for 6G communication technology
(Springer, 2023) Alfhaid, Latifah Hamad Khalid; Qasrawi, Atef Fayez
Herein, LaGe2 thin films with thickness of 150 nm are grown on thin layers of indium by the thermal evaporation technique under a vacuum pressure of 10?5 mbar. The films are structurally, morphologically, compositionally and electrically characterized. It is observed that thin films of LaGe2 are polycrystalline in nature, comprising slightly excess germanium in their structure. To establish their applicability in communication technology, two In/LaGe2/Ag and In/LaGe2/C electrical channels are formed. Both of the channels performed as negative resistance and capacitance sources. The channels exhibited microwave cutoff frequency exceeding 200 GHz. The resonance in the In/LaGe2/Ag and In/LaGe2/C channels dominates at driving frequencies of 1.21 GHz and 1.42 GHz, respectively. The measured impedance, magnitude of reflection coefficient (S11 parameter), return loss and voltage standing wave ratio spectra confirmed the suitability of the LaGe2 thin films for wireless 6G communication technology.
Enhanced crystallinity, optical conductivity and terahertz cutoff frequency of stacked layers of FeSe2 by Al nanosheets
(Elsevier, 2023) Qasrawi, Atef Fayez; Toubasi, Ahmad J.
Herein a 250 nm thick two stacked layers of FeSe2 (abbreviated as FF) thin films and FF stacks comprising aluminum nanosheets of thicknesses of 50 nm (FAF) are studied. Amorphous FeSe2 thin films are deposited using thermal evaporation technique under a vacuum pressure of 10-5 mbar. It is observed that insertion of Al nanosheets induced the evolution of orthorhombic phase of FeSe2. nanowire and elongated rectangular grains are also formed. Optically Al nanosheets enhanced the light absorption by 4.1 times and redshifted the indirect/direct energy band gaps from 2.80/2.49 eV to 2.42/1.85 eV, respectively. It also improved the optical conductivity and terahertz cutoff frequency as well. In addition the optical conductivity parameters of FF and FAF terahertz resonators are determined by the Drude-Lorentz approach. It is observed that in the infrared range of light Al nanosheets improved the drift mobility of FF from 2.06 cm2/Vs to 12.55 cm2/Vs. The hole density is reduced and the scattering time constant at femtosecond level is increased. FF and FAF terahertz resonators performed as optical filters suitable for terahertz technology applications with terahertz cutoff frequency varying in the range of 17.2-300 THz.
Production of PtInx thin films by the pulsed laser welding technique
(Springer, 01.08.2023) Alfhaid, Latifah Hamad Khalid; Qasrawi, Atef Fayez
Herein, PtInx nanosheets are fabricated by the pulsed laser welding technique (PLW) in an argon atmosphere within seconds from stacked layers of Pt (150 nm) and In (150 nm). Pt/In stacked layers coated by thermal evaporation under a vacuum pressure of 10?5 mbar are exposed to pulsed laser irradiation. During the welding process, the pulse width, repetition frequency and arc voltage of the laser are all varied. It is observed that the formed PtInx alloys are highly sensitive to the laser welding conditions. A new phase of PtInx alloys, referred to as PtIn4, is obtained and shown to favor a monoclinic crystal structure. PtIn4 displayed a high microwave cutoff frequency exceeding 100 GHz and negative capacitance effect. Modeling of the capacitance spectra in accordance with the Drude–Lorentz approach for ac conduction showed that converting stacked layers of Pt/In into thin films of PtIn4 form by PLW improves the electrical conductance and the drift mobility of the films. A 900-fold enhancement in mobility is achieved via the PLW technique. The characteristics of the produced PtIn4 thin films, including the negative capacitance (NC) effects and the cutoff frequency values, make the films attractive candidates for use as the active layer to produce NC thin film transistors and as band filters suitable for 6G technology.
Lead selenide thin films designed for laser sensing and visible light communications
(Springer, 2023) Khusayfan, Najla M.; Qasrawi, Atef Fayez; Khanfar, Hazem K.; Alharbi, Seham R.
Herein thin films of PbSe are coated onto amorphous glass, amorphous silicon (a?Si) and crystalline n?type Si (n?Si) wafers by the thermal evaporation technique under a vacuum pressure of 10? 5 mbar. The films are structurally, morphologically, compositionally, optically and electrically characterized. Strong effect of the nature (amorphous or crystalline) and type (Si or glass) of the substrate on the physical properties of lead selenide films is detected. Of these properties the crystallite sizes decreased and the microstrain, the stacking faults and defect density increased and the energy band gap is blue shifted when (a, n)-Si substrates replaces glass. In addition, the use of crystalline n?Si substrates instead of a?Si removed the free carrier absorption from a?Si/ p?PbSe improving the quantum efficiency of the devices. Opto-electronically, n?Si/p?PbSe films showed photosensor characteristics that suit both visible light and infrared technology applications. The photosensors displayed high current responsivity, external quantum efficiency percentages and response times reaching respective values of 1.4 A/W, 172% and 60 ?s. In addition, the n?Si/p?PbSe photosensors which were used as detectors to receive wireless light signals generated from light pulses of 10 kHz frequencies showed smart features nominating them as promising devices for laser sensing and visible light communication technology.
La/Ge stacked nanosheets designed as optical resonators, microwave oscillators and 5 G/6 G gigahertz receivers
(Optik, 2023) Alkhamisi, Manal M.; Qasrawi, Atef Fayez; Khanfar, Hazem K.
Glass/Ge and La/Ge stacked layers, 100 nm thick, were prepared via thermal evaporation under a vacuum pressure of 10-5 mbar. Structural analysis confirmed amorphous growth of Ge nanosheets. Optically coating Ge onto La improved light absorption, energy band gap, and dielectric responses. In addition, dielectric spectra fitting using Lorentz approach showed increased free electron density, plasmon frequency, and drift mobility (up to 1153 cm2/Vs) in Ge due to lanthanum presence. Moreover, LGA Schottky barrier devices (La/Ge/Au) exhibited tunneling-type current conduction with 0.815 eV barrier height and 40 nm width. Resistance spectra of these Schottky barriers displayed negative resistance near 0.40 GHz, while capacitance spectra showed resonance-antiresonance behavior. La/Ge and LGA interface can be utilized for optical receivers and microwave resonators in 5 G/6 G technologies.

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