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Electrical characterization of HVPE GaN containing different concentrations of carbon dopants
摘要： A comprehensive study of the electrical characteristics in Schottky diodes made of GaN:C grown by HVPE technology has been reported. The Schottky junctions were made of Ni/Au (25/200 nm) metal stack and ohmic contacts were fabricated by the Ti/Al/Ni/Au (30/90/20/100 nm) e-beam deposition of the metal thin-films followed by the rapid thermal annealing. A good quality of the fabricated Schottky diodes has been proved by considering the transient shape using a pulsed technique of the barrier evaluation under linearly increasing voltage (BELIV). The concentrations of equilibrium carriers of 1×1011 cm-3 and of 2×1010 cm-3 have been evaluated for relatively low and high carbon density doped samples, respectively, using photo-capacitance characteristics dependent on excitation intensity. The effective mobility of carriers of μeff=610 cm2/Vs has been estimated by considering the serial resistance variations dependent on excitation density, through analysis of delay times appeared in formation of peaks within BELIV transients. The optical deep level transient spectroscopy has shown that thermal emission from the rather shallow centres prevails. The centres, ascribed to vacancies as well as to carbon on Ga site, have been identified. It has been demonstrated that Schottky junctions made of heavy carbon doped (NC≥1018 cm-3) HVPE GaN material are capable to withstand voltages of ≥300 V.
关键词： barrier evaluation by linearly increasing voltage pulsed technique,transient current technique,Schottky diodes,carbon doped HVPE GaN grown on Ammono substrates,deep level transient spectroscopy
更新于2025-09-23 15:21:21
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Local photo-excitation of shift current in noncentrosymmetric systems
摘要： Photocurrent in solids is an important phenomenon with many applications including the solar cells. In conventional photoconductors, the electrons and holes created by light irradiation are separated by the external electric field, resulting in a current flowing into electrodes. Shift current in noncentrosymmetric systems is distinct from this conventional photocurrent in the sense that no external electric field is needed and, more remarkably, is driven by the Berry phase inherent to the Bloch wavefunction. It is analogous to the polarization current in the ground state but is a dc current continuously supported by the nonequilibrium steady state under the pumping by light. Here we show theoretically, by employing Keldysh–Floquet formalism applied to a simple one-dimensional model, that the local photo excitation can induce the shift current which is independent of the position and width of the excited region and also the length of the system. This feature is in stark contrast to the conventional photocurrent, which is suppressed when the sample is excited locally at the middle and increases towards the electrodes. This finding reveals the unconventional nature of shift current and will pave a way to design a highly efficient photovoltaic effect in solids.
关键词： nonequilibrium Green’s function method,shift current,photovoltaic effect
更新于2025-09-23 15:21:21
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Characteristics of GeSn-based multiple quantum well heterojunction phototransistors: a simulation-based analysis
摘要： Introduction of multiple quantum wells (MQWs) is an efficient way to enhance the light absorption capability in phototransistors. Direct band gap Ge1?xSnx alloy (x?>?0.08) having large absorption coefficient is an attractive material for heterojunction phototransistors (HPTs) compatible with CMOS platform. In this work, simulations are employed to obtain current gain, responsivity and collector current characteristics of Ge/GeSn/Ge HPTs with incorporation of MQWs (Ge0.87Sn0.13/Ge0.83Sn0.17) in the base region. The performances of bulk, single quantum well and MQW HPT structures are examined and compared. Best performance is shown by HPTs having MQW structure over a wide range of base emitter voltage.
关键词： simulation,current gain,heterojunction phototransistors,responsivity,GeSn,multiple quantum wells
更新于2025-09-23 15:21:21
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[IEEE 2018 20th International Symposium on High-Current Electronics (ISHCE) - Tomsk, Russia (2018.9.16-2018.9.22)] 2018 20th International Symposium on High-Current Electronics (ISHCE) - Cherenkov Ka-Band Oscillator with 45% Efficiency of Beam-to-Microwave Power Conversion
摘要： The paper describes a study of a new relativistic microwave Cherenkov generator of millimeter wavelength range with the transverse dimension of the electrodynamic system D>2.5λ, where D is the average diameter of the slow wave structure, and λ is the radiation wavelength. The investigations were carried out with a high-current SINUS-200 electron accelerator at a voltage of 473 kV and an electron beam current of 3.8 kA. The use of several, complementing each other, mechanisms of suppression of parasitic waves provides stable microwave generation at a specified frequency of 36.4 GHz. The microwave power in the experiment 804 MW with 45% beam-to microwave power conversion.
关键词： amplitude modulation of high-current electron beam,slow wave structures,Cherenkov radiation,electromagnetic radiation
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Effect of thermal pre-treatment on thermionic emission current stability from carbon nanotube forests
摘要： Carbon nanotube forests have great potential as efficient thermionic electron emitters due to a highly localized optical heating effect (“Heat Trap”). In past experiments, we observed a rapid decay in the emission current. In this work, we demonstrate that a relatively stable emission current can be achieved if the nanotube forest is pre-heated to 300 °C for 4 hours priors to electron emission. We attribute this improved current stability to the removal of reactant species, such as water trapped within the nanotube forest network.
关键词： Heat Trap,outgassing,lifetime,Carbon nanotubes,current stability,cathode,thermionic emission
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Stable and low noise field emission from single p-type Si-tips
摘要： Single gated p-type Si-tips with two different tip radii were fabricated. An emission current of 2.40 μA was measured for the sharp-edged tip at a voltage of 170 V. In contrast, a stable and reproducible emission behavior was observed with an increased tip radius resulting in a pronounced saturation region between 90 V and 150 V, but merely an emission current of 0.55 μA at 150 V. More remarkable is the stable emission behavior with fluctuation of ± 4 % during a measurement period of 30 minutes. The integral emission current in a homogeneous tip array (16 emitters) showed nearly the same I-V characteristics compared to the single tip and is therefore, most dominated by only a stable single tip in the array.
关键词： gate-electrode,p-type Si-tips,low current fluctuations,emission stability,field emission
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Arrays of Si Field Emitter Individually Regulated by Si Nanowires High Breakdown Voltages and Enhanced Performance
摘要： We fabricate Si field emitter arrays (FEAs) with integrated Si nanowire current limiters and investigate a method to enable higher voltage operation, which can potentially increase achievable current densities. In this work, we focus on the dielectric breakdown occurring in the vicinity of the nanopillar. A deeper etch is shown to increase the breakdown voltage but at the expense of poorer field emission characteristics possibly due to the loss of mechanical support or increased surface states.
关键词： field emitter arrays,Silicon,breakdown voltage,current limiters
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Fluctuations of the emission characteristics of multi-tip field cathodes
摘要： Report presents a complex experimental study of the fluctuations in the emission characteristics of multi-tip field cathodes based on composites "disordered carbon nanotubes in a polymer matrix". The objects of the study: correlation of the glow patterns of the field emission projector with the level of the macroscopic emission current, emission sites activity, distribution of the current load on the emission sites, field enhancement factor of the individual emission sites, dependence of the current-voltage characteristics and effective emission parameters on the voltage and vacuum levels, formation of a calibration grid on the SK-diagram, modeling of the adsorption/desorption processes on the emitter surface.
关键词： emitter surface analysis,field emission images,current fluctuation,nanocomposite,field emission,carbon nanotubes,IVC
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Nanogranular Compound Material Layers Serve as Storage for Infra-red to Ultra-Violet Photons for the Energy Supply for Electric Machines
摘要： Hyper-Giant conducting nanogranular compound materials, which serve as IR photon detectors allow to use BOSON-current transport at room temperature with GA/cm2 current carrying capability for Energy applications
关键词： Room temperature,Bosons having parallel spin,Boson-current transport,Energy supply for electric machines
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Commutable cold cathodes based on vertically aligned carbon nanotubes with a buried modulation electrode
摘要： A new design of commutable CNT emitters cathode with an on-chips gate has been investigated. Both fabrication and field emission proprieties of a buried gate cathode have been demonstrated. Current modulation by applying a small bias on the buried gate has been performed. This design shows excellent modulation properties and a high robustness.
关键词： carbon nanotubes,current modulation,field emission,buried gate
更新于2025-09-23 15:21:21