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Effects of Mg incorporation in cubic GaN films grown by PAMBE near Ga rich conditions
摘要： The structural and electrical properties of Mg-doped cubic GaN epi-layers grown by plasma-assisted molecular beam epitaxy (PAMBE) near Ga rich conditions are investigated. The diffraction of high-energy reflected electrons (RHEED) in situ, in addition to structural studies of X-ray diffraction, show that the fraction of hexagonal and crystal twinning inclusions decreases when the Mg flux increases. The condition for the higher incorporation of Mg where the electrical properties are optimized is highly sensitive to the flow ratio Mg/Ga. The p-doping level steadily increases with increasing Mg flux. The Mg concentration obtained by secondary ion mass spectroscopy (SIMS) from samples grown at Mg temperatures from 200 °C to 700 °C are in a range between 2 × 10^19 to 2 × 10^20 atoms/cm^3. The highest mobility and p-type doping level achieved, determined from Hall measurements, were 28.2 cm^2/V-s and 2 × 10^19 cm^-3, respectively. We corroborate that the Mg doped c-GaN films are suitable for the construction of optoelectronic devices based on cubic III-Nitrides.
关键词： Plasma-assisted molecular beam epitaxy,Cubic GaN diode,Mg p-type doping
更新于2025-09-23 15:22:29
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Contact Engineering for Dual-Gate MoS <sub/>2</sub> Transistors Using O <sub/>2</sub> Plasma Exposure
摘要： The benefits of O2 plasma exposure at the contact regions of dual-gate MoS2 transistors prior to metal deposition for high performance electron contacts is studied and evaluated. Comparisons between devices with and without the exposure demonstrate significant improvements due to the formation of a high-quality contact interface with low electron Schottky barrier (~0.1 eV). Topographical and interfacial characterization are used to study the contact formation on MoS2 from the initial exfoliated surface through the photolithography process and Ti deposition. Fermi level pinning near the conduction band is shown to take place after photoresist development leaves residue on the MoS2 surface. After O2 plasma exposure and subsequent Ti deposition, Ti scavenges oxygen from MoOx and forms TiOx. Electrical characterization results indicate that photoresist residue and other contaminants present after development can significantly impact electrical performance. Without O2 plasma exposure at the contacts, output characteristics of MoS2 FETs demonstrate non-linear, Schottky-like contact behavior compared to the linearity observed for contacts with exposure. O2 plasma allows for the removal of the residue present at the surface of MoS2 without the use of a high temperature anneal. A low conduction band offset and superior carrier injection are engineered by employing the reactive metal Ti as the contact to deliberately form TiO2. Dual-gate MoS2 transistors with O2 plasma exposure at the contacts demonstrate linear output characteristics, lower contact resistance (~20× reduction), and higher field effect mobility (~15× increase) compared to those without the treatment. In addition, these results indicate that device fabrication process induced effects cannot be ignored during the formation of contacts on MoS2 and other 2D materials.
关键词： TiO2,MoS2,contact resistance,O2 plasma,photoresist residue,MOSFETs,contacts
更新于2025-09-23 15:22:29
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Contact Angle Relaxation and Long-lasting Hydrophilicity of Sputtered Anatase TiO <sub/>2</sub> Thin Films by Novel Quantitative XPS Analysis
摘要： The contact angle relaxation of TiO2 surfaces is an important problem that must be understood, particularly for long-lasting hydrophilicity under dark conditions. The relaxation of sputtered anatase TiO2 thin films over a long time (~22 days) in an atmospheric environment was observed using quantitative XPS analysis. A new peak was identified as H2O within a donor-acceptor complex at ~2.57 eV above the lattice oxygen peak. This donor?acceptor complex turns out to be a key factor for long lasting hydrophilicity, and our model is presented. Adventitious carbon contamination was not the main cause of the contact angle relaxation. Instead, samples with lower amounts of donor?acceptor complexes (IDAC/Ibulk ≤ ~5%) underwent contact angle relaxation over time, and samples with a high density of donor?acceptor complexes (IDAC/Ibulk ≥ ~10%) showed good hydrophilicity (contact angle ≤ 20°) over 22 days. Larger amounts of basic Ti?OH relative to acidic OHbridge (ITi?OH/Ibridge ≥ 1) resulted in greater amounts of donor?acceptor complexes (IDAC/Ibulk ≥ ~10%). Thus, basic Ti?OH groups interact with H2O by forming a strong electrostatic donor?acceptor complex, leading to long-lasting hydrophilicity. Indeed, TiO2 was transformed to show long lasting hydrophilicity by high-density oxygen plasma treatment by forming sufficient Ti?OH groups and H2O molecules in the donor?acceptor complexes. Contact angle relaxation is closely related to the interactions between water molecules and the TiO2 surface in the dark. It is suggested that the relaxation depends on the number of electrostatic donor?acceptor complexes. This study provides new insight by linking theoretical studies with the experimental contact angle at the TiO2 surface in an ambient environment and is the first study that provides the presented relaxation mechanism.
关键词： Hydrophilicity,Sputtering,Plasma treatment,Contact angle relaxation,XPS analysis,Donor-acceptor complex,TiO2 thin films
更新于2025-09-23 15:22:29
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Electromagnetic wave cloaking and scattering around an antiresonance-resonance symmetrical pair in the frequency domain
摘要： Cloaking and scattering cancellation of electromagnetic waves have attracted much attention since they allow control of rf and light waves and are of scientific interest. The analytical results demonstrated in this paper reveal that plasmonic cloaking, which is one of the schemes for scattering cancellation, occurs in the vicinity of Tonks-Dattner resonances in the frequency domain, where resonances enhance wave scattering. This antiresonance-resonance pair for cloaking and scattering is cross-correlated by the symmetrical locations above and below the electron plasma frequency, respectively. However, the cloaking effect is almost independent of electron collisions with neutral particles, whereas scattering at resonance is fairly sensitive to them, leading to unclear resonance. An experimental verification of this analytical prediction is performed for the cloaking effect on working points passing through the cloaking condition and approaching resonance, which is dynamically controlled by changing the electron density. Numerical calculations based on a model configuration similar to the experimental setup confirm scattering cancellation and an increase in scattering as the points get close to the resonance condition. These results are direct evidence of scattering cancellation with a uniform epsilon-near-zero material and demonstrate the effectiveness of plasma as a cloaking material.
关键词： plasma,electromagnetic cloaking,scattering cancellation,Tonks-Dattner resonances,epsilon-near-zero material
更新于2025-09-23 15:22:29
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Design, Development, and Operation of Seven Channels' 100-GHz Interferometer for Plasma Density Measurement
摘要： A seven-channel microwave interferometer (100 GHz) is designed, developed, and used to measure the radial profile of the plasma density (ne) in Aditya tokamak. The resolution of the density measurement is ne = 2 × 10^11 cm^-3. The spatial and time resolutions are 7 cm and 10 μs, respectively. The chord-averaged measurements from seven channels are Abel inverted to obtain the radial profile of the plasma density. Plasma density measured by the microwave interferometer is well matched with that measured by the Thomson scattering diagnostics.
关键词： Density measurements,interferometry,plasma measurements,microwave circuits
更新于2025-09-23 15:22:29
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Analysis of Optical Plasma Monitoring in Plasma-Enhanced Atomic Layer Deposition Process of Al <sub/>2</sub> O <sub/>3</sub>
摘要： A noninvasive, optical plasma monitoring method in plasma-enhanced atomic layer deposition (PEALD) process for nanoscale water vapor barrier film is presented. Any equipment malfunction, as well as a deviation in the condition of individual components can easily jeopardize the process result. Al2O3 deposition process was employed in this research as a test vehicle, and high-speed optical plasma monitoring was demonstrated. It is shown that optical plasma monitoring is useful for not only measuring plasma pulses in real time, but also for the detection of any variation in plasma condition which enables inferring plasma dynamics for advanced process control in nanoscale thin film deposition process.
关键词： PEALD,Process Monitoring,Plasma Diagnostics,Fault Detection
更新于2025-09-23 15:22:29
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[IEEE 2018 China International SAR Symposium (CISS) - Shanghai (2018.10.10-2018.10.12)] 2018 China International SAR Symposium (CISS) - Imaging and Detection of Moving Targetsbased on Spaceborne Video SAR Mode
摘要： Yttrium fluoride (YF3) films were grown on sapphire substrate by a radio frequency magnetron using a commercial ceramic target in a vacuum chamber. The structure, composition, and plasma etching behavior of the films were systematically investigated. The YF3 film was deposited at a working pressure of 5 mTorr and an RF power of 150 W. The substrate-heating temperature was increased from 400 to 700 °C in increments of 100 °C. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction results confirmed an orthorhombic YF3 structure was obtained at a substrate temperature of 700 °C for 2 h. X-ray photoelectron spectroscopy revealed a strongly fluorinated bond (Y–F bond) on the etched surface of the YF3 films. HRTEM analysis also revealed that the YF3 films became yttrium-oxyfluorinated after exposure to fluorocarbon plasma. The etching depth was three times lower on YF3 film than on Al2O3 plate. These results showed that the YF3 films have excellent erosion resistance properties compared to Al2O3 plates.
关键词： yttrium fluoride,plasma processing equipment,films
更新于2025-09-23 15:22:29
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Growth Condition-Oriented Defect Engineering for Changes in Au–ZnO Contact Behavior from Schottky to Ohmic and Vice Versa
摘要： ZnO has the built-in characteristics of both ionic and covalent compound semiconductors, which makes the metal–ZnO carrier transport mechanism quite intricate. The growth mechanism-centric change in ZnO defect density and carrier concentration also makes the contact formation and behavior unpredictable. This study investigates the uncertainty in Au–ZnO contact behavior for application-oriented research and the development on ZnO nanostructures. Herein, we explain the phenomenon for how Au–ZnO contact could be rectifying or non-rectifying. Growth method-dependent defect engineering was exploited to explain the change in Schottky barrier heights at the Au–ZnO interface, and the change in device characteristics from Schottky to Ohmic and vice versa. The ZnO nanorods were fabricated via aqueous chemical growth (ACG) and microwave-assisted growth (MAG) methods. For further investigations, one ACG sample was doped with Ga, and another was subjected to oxygen plasma treatment (OPT). The ACG and Ga-doped ACG samples showed a quasi-Ohmic and Ohmic behavior, respectively, because of a high surface and subsurface level donor defect-centric Schottky barrier pinning at the Au–ZnO interface. However, the ACG-OPT and MAG samples showed a more pronounced Schottky contact because of the presence of low defect-centric carrier concentration via MAG, and the removal of the surface accumulation layer via the OPT process.
关键词： oxygen plasma treatment,nanorod,ZnO,crystal defects,microwave,metal-semiconductor contact
更新于2025-09-23 15:22:29
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P-1.3: The conductivity modulation of amorphous zinc tin oxide thin film by Ar plasma treatment
摘要： We propose a method to form low-resistance amorphous zinc tin oxide thin film (a-ZTO) by Ar plasma. The results show that the Ar plasma treatment can effectively decrease the resistivity of the a-ZTO. The ZTO film treated with Ar plasma at suitable time and moderate operating power, exhibits a low sheet resistance of 2.3 kΩ/□. With the help of PECVD-SiOx coverage layer, the sheet resistance of Ar-plasma treated ZTO is enhanced and increases only one order of magnitude after annealing at 230 ℃. As a result, an optimized Ar plasma treatment for fabrication of low-resistance a-ZTO film is presented.
关键词： amorphous zinc tin oxide,thermal stability,Ar plasma treatment,low-resistance
更新于2025-09-23 15:22:29
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Plasma-Assisted Chemical Vapor Synthesis of Aluminum-Doped Zinc Oxide Nanopowder and Synthesis of AZO Films for Optoelectronic Applications
摘要： Transparent conducting oxide aluminum-doped zinc oxide (AZO) nanoparticles were synthesized by a plasma-assisted chemical vapor synthesis route using zinc nitrate and aluminum nitrate as the precursors. The injected precursors vaporized in the plasma flame, followed by vapor-phase reaction and subsequent quenching of the vaporized precursors, producing nanosized AZO powder. The amount of aluminum nitrate was varied to obtain samples with 2 at.%, 4 at.% and 8 at.% Al, designated as AZO1, AZO2 and AZO3, respectively. The XRD patterns of the AZO1 and AZO2 nanoparticles indicated the presence of a wurtzite structure without any alumina peaks except in the AZO3 sample, and scanning electron microscopy micrographs revealed spherical particles. The magnetization measurements revealed a ferromagnetic behavior at room temperature in the AZO1 sample, and the ferromagnetic order is decreased in the high field region with an increase in the Al doping amount. AZO thin films were deposited on glass substrates by spin-coating a dispersion of nanoparticles. All the AZO films had a hexagonal wurtzite structure and exhibited a c-axis preferred orientation perpendicular to the substrate. The Hall effect measurements yielded a minimum resistivity of 9.9 × 10?? Ω cm for the AZO2 film and optical transmission of 80% for both the AZO1 and AZO2 films. However, with 8 at.% Al in the AZO3 film, deterioration in crystallinity, electrical and optical properties were observed. Post-annealing of the AZO1 film in H2 atmosphere caused a significant decrease in resistivity from 1.2 × 10?3 Ω cm to 8.7 × 10?? Ω cm. The optical band gap energies of the AZO films were determined from the transmission spectra. The blue shift in the band gap from 3.2 eV to 3.28 eV, observed with an increase in Al doping, was interpreted by the Burstein–Moss effect. The photoluminescence spectra of the AZO films revealed a UV near-band edge emission and a green emission peak.
关键词： Plasma,optoelectronics,doped-zinc oxide,chemical vapor synthesis
更新于2025-09-23 15:22:29