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Effects of Parasitic Region in SiC Bipolar Junction Transistors on Forced Current Gain
摘要： Effects of a parasitic region in SiC BJTs on conductivity modulation and a forced current gain (????) were investigated by using TCAD simulation with various device structures. By introducing an Al+-implanted region below the base parasitic region, ???? can be improved because the implanted region can reduce the base spreading resistance, leading to alleviation of debiasing effect. ???? in devices with various parasitic areas, whose base spreading resistances were reduced by the Al+-implantation, were compared. We found that ???? can be enhanced by expanding the parasitic area if the base spreading resistance is sufficiently reduced. The higher ???? is attributed to an expanded conductivity-modulated region. The collector current spreading in the collector layer and hole injection from the parasitic region as well as from the intrinsic region can play a role to evoke conductivity modulation. Thus, the larger parasitic region can expand the conductivity-modulated region, which results in expansion of an active area and the enhancement of ????, though a higher base voltage is required.
关键词： forced current gain,conductivity modulation,parasitic region,hole injection,SiC BJT,base spreading resistance
更新于2025-09-23 15:21:01
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Controlled switching of a single CuPc molecule on Cu(111) at low temperature
摘要： Low temperature measurements of the tunneling current as a function of the applied bias voltage have been performed on a dense constant-height grid above individual copper phthalocyanine molecules adsorbed on a Cu(111) surface. By appropriate tuning of the applied bias, the molecule can be reversibly switched between two configurations in which pairs of opposite maxima appear rotated by 90? in the tunneling current map. The underlying conformations are revealed by density functional calculations including van der Waals interactions: a C2v symmetric ground state and two energetically equivalent states, in which the molecule is twisted and rotated around its center by ±7?. For tip biases above 200 mV position-dependent current switching is observed, as in previous measurements of telegraph noise [Schaffert et al., Nat. Mater. 12, 223 (2013)]. In a small voltage interval around zero the measured current becomes bistable. Switching to a particular state can be initiated by sweeping the voltage past well-defined positive and negative thresholds at certain positions above the molecule or by scanning at constant current and a reduced reverse bias.
关键词： density functional calculations,van der Waals interactions,tunneling current,copper phthalocyanine,Cu(111) surface,bistable current
更新于2025-09-23 15:19:57
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Performance Problem of Current Differential Protection of Lines Emanating from Photovoltaic Power Plants
摘要： The amplitude and phase angle of the fault current in photovoltaic power plants (PVPPs) are significantly influenced by the control system of the grid-connected inverters, unlike in a conventional synchronous source. Hence, PVPPs may adversely affect the performance of the current differential protection designed for synchronous sources-based power grids. In order to study the performance problem of current differential protection on AC transmission lines, an analytical expression of the fault current in the PVPPs was deduced, and the fault current characteristic was extensively analyzed. Based on this analysis, the ratio of differential current over restraint current was initially derived in this study; this ratio is observed to be affected by the control system parameters, power grid system parameters, fault resistance, and fault types. Moreover, the dynamic characteristics of this ratio can be clearly observed based on a three-dimensional diagram. Furthermore, the operating performance of the current differential protection was analyzed under different influencing factors. The mathematical analysis presents that the amplitude ratio of the fault current on both sides of the line is larger than nine and that current differential protection will operate reliably in any case. Meanwhile, the theoretical analysis and simulation results show that the current phase angle difference may become an obtuse angle in case of an ungrounded fault, which will cause inaccurate operation of the current differential protection. The results of this study will provide guidance for the engineering application of current differential protection in case the PVPPs are connected to a power grid.
关键词： performance problem,photovoltaic power plants,current differential protection,fault current behavior
更新于2025-09-23 15:19:57
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Determination of the series resistance of a solar cell through its maximum power point
摘要： A simple analytical approach has been developed to determine the series resistance, Rs, of a solar cell. The method adopted here depends only on the knowledge of the open-circuit voltage, Voc, and the current and voltage at the maximum power point, Isc and Vmp respectively. This approach, based on a knowledge of these operating output parameters of the cell, provides a theoretical framework for an existing computer simulated approach which has been widely used in industries.
关键词： series resistance,short-circuit current,five-parameter model,light generated current,solar cell,shunt resistance
更新于2025-09-23 15:19:57
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Utility of copper oxide nanoparticles (CuO-NPs) as efficient electron donor material in bulk-heterojunction solar cells with enhanced power conversion efficiency
摘要： In the present work, we have endeavored the utilization of wet-chemically synthesized copper oxide nanoparticles (CuO-NPs) as the active layer in hybrid bulk heterojunction (BHJ) solar cells. The BHJs with CuO-NPs display significantly different physics from customary BHJs, and prove a noteworthy improvement in their performance. It is noted that with the addition of CuO-NPs, the morphology of the photoactive layer endures significant changes. Incorporating CuO-NPs is an additional paradigm for BHJs solar cells which enhances the photocurrent density from 9.43 mA/cm2 to 11.32 mA/cm2 and the external quantum efficiency as well. Also the power-conversion efficiency (PCE) improved from 2.85 % to 3.82 % without harming the open circuit voltage and the fill factor. The enhancement in PCE achieved here makes it worthy to design high-performance organic solar cells holding inorganic nanoparticles.
关键词： thin films,Bulk heterojunction,Solar cells,external quantum efficiency,Copper oxide nanoparticles,photo current density
更新于2025-09-23 15:19:57
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Equivalent Circuit Parameters of Hybrid Quantum-Dot Solar Cells
摘要： We experimentally investigate the equivalent circuit parameters of hybrid quantum-dot (QD) solar cells consisted of InAs/GaAs and GaSb/GaAs QDs. The hybrid QD solar cell samples are fabricated by stacking one pair and three pairs of InAs/GaAs and GaSb/GaAs QD layers. Four equivalent circuit models are applied to fit the experimentally obtained current-voltage characteristics of the investigated samples. The relevant circuit parameters are photocurrent, reverse saturation current, diode ideality factor, series resistance, and shunt resistance. The best fitted model of all samples contains both series and shunt resistances. According to the fitting result, the diode ideality factor of 2, which indicates the dominant recombination current, is always obtained. Comparing the extracted parameters from two single-pair hybrid QD solar cells, the effects of structural stacking sequence can be discussed in term of light absorption and carrier storage properties. We have found that an increase of stacking number from one pair to three pairs deteriorates the solar cell performance. This might be caused by an excessive total QD layer thickness or a presence of dislocation defects in that sample.
关键词： Parameter Extraction,Current-Voltage Characteristics,Solar Cell,Quantum Dot
更新于2025-09-23 15:19:57
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Suppressing Efficiency Roll-Off at High Current Densities for Ultra-Bright Green Perovskite Light-Emitting Diodes
摘要： Perovskite light-emitting diodes (PeLEDs) have undergone rapid development in the last several years with external quantum efficiencies (EQE) reaching over 21%. However, most PeLEDs still suffer from severe efficiency roll-off (droop) at high injection current densities, thus limiting their achievable brightness and presenting a challenge to their use in laser diode applications. In this work, we show that the roll-off characteristics of PeLEDs are affected by a combination of charge injection imbalance, nonradiative Auger recombination, and Joule heating. To realize ultrabright and efficient PeLEDs, several strategies have been applied. First, we designed an energy ladder to balance the electron and hole transport. Second, we optimized perovskite materials to possess reduced Auger recombination rates and improved carrier mobility. Third, we replaced glass substrates with sapphire substrates to better dissipate joule heat. Finally, by applying a current-focusing architecture, we achieved PeLEDs with a record luminance of 7.6 Mcd/m2. The devices can be operated at very high current densities (J) up to ~ 1 kA/cm2. Our work suggests a broad application prospect of perovskite materials for high-brightness LEDs and ultimately a potential for solution-processed electrically pumped laser diodes.
关键词： Joule heat,efficiency roll-off,Auger recombination,charge injection balance,high injection current density,ultrahigh brightness,perovskite light emitting diodes
更新于2025-09-23 15:19:57
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Improving modulation bandwidth and optical power of GaNa??based blue LED by hollowa??runway active area
摘要： We demonstrate a higher-bandwidth and optical power GaN-based blue light-emitting diode for visible-light communication applications. By using a hollow-runway active area and hollow-runway current-confined aperture structure, we obtain an electrical-to-optical (E-O) 3 dB bandwidth (f?3 dB) significantly higher than that of a rectangle-structure LED with the same epitaxial structure and area of active area. Meanwhile, its optical power can reach 48.65 mW, even higher than a rectangle-structure LED (45.33 mW). Eight hollow-runway LEDs connected in series are called hollow-runway-chip-array LEDs (HRCA-LEDs) and eight rectangle-structure LEDs connected in series are called rectangle-chip-array LEDs (RCA-LEDs), and they are fabricated into a new device on the same substrate. The f?3 dB and the optical power of the device are ~98.5 MHz and ~712.3 mW, respectively, at 50 mA. HRCA-LEDs are used as communication module that can provide data transmission and lighting and RCA-LEDs as a lighting module for enhancing the overall lighting capability of the device. Its luminous flux is 203.57 lm and efficacy is 87.00 lm/W at 50 mA.
关键词： electrical-to-optical (E-O) 3 dB bandwidth,visible-light communication,current-confined apertures,hollow-runway structure
更新于2025-09-23 15:19:57
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[IEEE 2019 21st International Middle East Power Systems Conference (MEPCON) - Cairo, Egypt (2019.12.17-2019.12.19)] 2019 21st International Middle East Power Systems Conference (MEPCON) - Experimental Realization for P&O Maximum Power Point Tracking Applied for Single-Stage Three-Phase Grid-Connected Photovoltaic System
摘要： This paper presents a point of care testing device for neurovascular coupling (NVC) from simultaneous recording of electroencephalogram (EEG) and near infrared spectroscopy (NIRS) during anodal transcranial direct current stimulation (tDCS). Here, anodal tDCS modulated cortical neural activity leading to hemodynamic response can be used to identify the impaired cerebral microvessels functionality. The impairments in the cerebral microvessels functionality may lead to impairments in the cerebrovascular reactivity (CVR), where severely reduced CVR predicts the chances of transient ischemic attack and ipsilateral stroke. The neural and hemodynamic responses to anodal tDCS were studied through joint imaging with EEG and NIRS, where NIRS provided optical measurement of changes in tissue oxy-(HbO2) and deoxy-(Hb) hemoglobin concentration and EEG captured alterations in the underlying neuronal current generators. Then, a cross-correlation method for the assessment of NVC underlying the site of anodal tDCS is presented. The feasibility studies on healthy subjects and stroke survivors showed detectable changes in the EEG and the NIRS responses to a 0.526 A/m2 of anodal tDCS. The NIRS system was bench tested on 15 healthy subjects that showed a statistically signi?cant (p < 0.01) difference in the signal-to-noise ratio (SNR) between the ON- and OFF-states of anodal tDCS where the mean SNR of the NIRS device was found to be 42.33 ± 1.33 dB in the ON-state and 40.67±1.23 dB in the OFF-state. Moreover, the clinical study conducted on 14 stroke survivors revealed that the lesioned hemisphere with impaired circulation showed signi?cantly (p < 0.01) less change in HbO2 than the nonlesioned side in response to anodal tDCS. The EEG study on healthy subjects showed a statistically signi?cant (p < 0.05) decrease around individual alpha frequency in the alpha band (8–13 Hz) following anodal tDCS. Moreover, the joint EEG-NIRS imaging on 4 stroke survivors showed an immediate increase in the theta band (4–8 Hz) EEG activity after the start of anodal tDCS at the nonlesioned hemisphere. Furthermore, cross-correlation function revealed a signi?cant (95% con?dence interval) negative cross correlation only at the nonlesioned hemisphere during anodal tDCS, where the log-transformed mean-power of EEG within 0.5–11.25 Hz lagged HbO2 response in one of the stroke survivors with white matter lesions. Therefore, it was concluded that the anodal tDCS can perturb the local neural and the vascular activity (via NVC) which can be used for assessing regional NVC functionality where con?rmatory clinical studies are required.
关键词： Hilbert-Huang transform,Electroencephalogram,neurovascular coupling,small vessel diseases,stroke,near infrared spectroscopy,transcranial direct current stimulation
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Study of Open-Circuit Voltage in CdTe/MgCdTe Double-Heterostructure Solar Cells with Different Hole Contacts
摘要： Model predictive control (MPC) has been widely advocated as a design strategy for many aspects of industrial electronics. The methodology has been strongly promoted by some researchers but has also attracted criticism from others. In this context, the purpose of this paper is twofold. First, we show that many existing and popular control strategies, including finite set MPC and linear controllers [proportional integral, proportional resonant (PR)], can be viewed as special cases of MPC. Second, we show that the predictive control framework allows one to embellish these classical control architectures with novel features and to design new and advanced control architectures to address various challenges posed by power electronics applications. The findings of the paper are supported by a practical example of designing of a novel form of PR controller with superior tracking performance and delay compensation, confirmed via simulation and experiments.
关键词： model predictive control (MPC),Control design,dc–ac power converters,pulsewidth modulation inverters,current control
更新于2025-09-23 15:19:57