Current Recovery Time Research Articles

The effect of trapping sites introduced by 1 MeV proton irradiation on the reverse current recovery time in Ga2O3-based Schottky diodes

The reverse current recovery time is an important parameter of diodes, fast rectifiers and transistors which determined their high-frequency properties and area of application. Defects in the structure may sufficiency reduce the cutoff frequency and lead to overheating. The reverse recovery of the low currents in the α- and β-Ga2O3 Schottky diodes was measured and analyzed in this study. The reverse recovery time in the β-Ga2O3-based Schottky diode is limited mainly by the relaxation of the RC-circuit formed by the equivalent diode circuit and can be very low (20 nsec in this case). Irradiation can introduce some defects in the structure, which may act as deep levels and prolong the relaxation. We have demonstrated experimentally that increasing serial resistance of the circuit lead to an increase in the reverse recovery time. But we can point an additional part of relaxation that can be attributed to the emission from deep levels in the forbidden gap of the semiconductor. It is shown that prolongation increases with the reverse recovery time but saturates. In the α-Ga2O3-based structures the reverse recovery time measured after proton irradiation was 6 μsec, twice as high than it can be expected from RC-circuit relaxation time. These deep levels can be associated with interstitial oxygen atoms. The results obtained can be used to improve the technology of crystal growth to produce Schottky diodes with a high boundary frequency.

A Simple Method to Extract the Thermal Resistance of GaN HEMTs From De-Trapping Characteristics

This paper proposes a new method for extracting the thermal resistance of GaN-based HEMTs using pulse recovery data. After the device temperature and trapping state are established from different quiescent power dissipations for several base-plate temperatures, the recovery profile of the drain current is measured. The recovery time is then used as a temperature-sensitive electrical parameter to extract the thermal resistance of the device. The proposed method has been applied to a Schottky-gate HEMT on SiC, for which a thermal resistance of 15.7 °C-mm/W was extracted, a value in good agreement with others reported for similar devices. Comparison with the one obtained from a step response is also done. Finally, the uncertainties of the proposed method related to the pulse width, temperature, percentage of the drain current recovery time, and averaging procedure are discussed.

Ag nanowires assisted CH3NH3PbBr3–ZnO heterostructure with fast negative photoconductive response

Due to its attractive interaction with light, negative photoconductivity (NPC) has received widespread attention and has been used in optoelectronic logic devices with excellent performance. However, long negative response time triggered by photogenerated carriers trapping mechanism became a bottleneck in further application. Therefore, an enhanced strategy that can speed up negative response is urgently needed. Herein, we prepared a zinc oxide microwire (ZnO MW)–silver nanowires (Ag NWs)–methylammonium lead halide perovskite (CH3NH3PbBr3) heterostructure with enhanced negative response than the previous NPC device. The Ag NWs with high mobility at the interface of ZnO and CH3NH3PbBr3 accelerate the photoresponse time from 50 to 5.4 s and improve the dark current recovery time by two orders of magnitude. This work provides a strategy to improve the negative response speed with simple operation, which represents a step toward applications in the field of fast NPC optoelectronics.

Current model predictive fault-tolerant control for grid-connected photovoltaic system

<abstract><p>This paper investigates the performance of the current model predictive control (CMPC) for controlling a two-stage transformerless grid-connected photovoltaic (PV) system under grid fault conditions. A maximum power point tracking (MPPT) controller was used to extract the maximum power of the PV panel. To stabilize the DC link and generate the reference current values, a proportional-integral (PI) controller was used. The CMPC strategy was implemented to control the output current of the inverter that connects the PV system to the utility grid. The system and control strategy were simulated via a MATLAB/Simulink environment. The performance of the proposed control strategy was investigated under fault conditions between the three-phase two-level inverter and the grid. Moreover, to validate the capability of the CMPC, comparative case studies were conducted between CMPC, PI, and sliding mode control (SMC) under grid fault. Case studies' results showed that under grid fault, CMPC did not introduce any overshoot or undershoot in the PV output DC current and power. However, PI and SMC produced undershoots of almost 15 kW for the output power and 45 A for the output current. Under the fault conditions, the active output power and three-phase current recovery time of the inverter was 50 ms using CMPC, compared to PI and SMC with recovery times of 80 ms and 60 ms, respectively. Moreover, a voltage dip of 75 V at the DC link voltage was recorded with CMPC under faulty conditions, while the voltage dips for PI and SMC were around 180 V.</p></abstract>

Investigation of a Highly Sensitive Au Nanoparticle-Modified ZnO Nanorod Humidity Sensor

In this article, pure ZnO and Au nanoparticle-modified (ANM) ZnO nanorods (NRs) were well prepared on a glass substrate via the hydrothermal method at 90 °C for 6 h, and the pure ZnO and ANM ZnO NR humidity sensors were fabricated. The crystal and optical properties of the ZnO and ANM ZnO NRs were investigated through scanning electron microscopy (SEM), XRD, photoluminescence (PL), and TEM analyses. The structures of the relative humidity (RH) sensors demonstrated high photo-to-dark current contrast ratios and short response and recovery times during RH measurement. The ANM ZnO NR RH sensor showed better humidity sensing performance than the pure ZnO NR humidity sensor. Under 80% RH, the results of photo-to-dark current contrast ratios, response time, and recovery time were 9.82, 192.44, and 122.42 s, respectively, better than those in pure ZnO NRs RH sensor. These results indicated that humidity sensing property could effectively be improved by Au nanoparticle adsorption.

Design Guidelines and Performance Tradeoffs in Recessed AlGaN/GaN Schottky Barrier Diodes

Critical design parameters for AlGaN/GaN Schottky barrier diodes (SBDs) are analyzed in this work using TCAD computations and detailed experiments. A comprehensive TCAD-based computational modeling approach is developed for GaN-based SBD. Breakdown mechanisms in SBD for unintentionally doped (UID) buffer, Fe-doped buffer and C-doped buffer are studied. For the first time, we have reported impact of anode recess, on breakdown and leakage behavior of SBD, in correlation with interface defects. Using these insights an optimum recess design strategy has been presented and is validated experimentally. Furthermore, for the first time, we have revealed critical repercussions of the field plate termination on SBD's breakdown, leakage as well as transient behavior. Forward and reverse recovery measurements were carried out to study the diode's transient performance as a function of field plate design. Various performance matrices such as diode current collapse, reverse current overshoot and reverse recovery time were studied experimentally as a function of field plate design. Moreover, the field plate-dependent electro-thermal behavior of SBD was studied using TCAD computations and experiments. Using the systematic device design approach we have experimentally demonstrated large periphery SBD with 15 A forward current at 5.5 V.

Investigation of current collapse and recovery time due to deep level defect traps in β-Ga2O3 HEMT

In this paper, drain current transient characteristics of β-Ga2O3 high electron mobility transistor (HEMT) are studied to access current collapse and recovery time due to dynamic population and de-population of deep level traps and interface traps. An approximately 10 min, and 1 h of recovery time to steady-state drain current value is measured under 1 ms of stress on the gate and drain electrodes due to iron (Fe)–doped β-Ga2O3 substrate and germanium (Ge)–doped β-Ga2O3 epitaxial layer respectively. On-state current lag is more severe due to widely reported defect trap EC – 0.82 eV over EC – 0.78 eV, −0.75 eV present in Iron (Fe)-doped β-Ga2O3 bulk crystals. A negligible amount of current degradation is observed in the latter case due to the trap level at EC – 0.98 eV. It is found that occupancy of ionized trap density varied mostly under the gate and gate–source area. This investigation of reversible current collapse phenomenon and assessment of recovery time in β-Ga2O3 HEMT is carried out through 2D device simulations using appropriate velocity and charge transport models. This work can further help in the proper characterization of β-Ga2O3 devices to understand temporary and permanent device degradation.

A Novel Configuration for Resistive SFCL with bifilar 2G tapes

Electrical faults on medium voltage electric power distribution systems can damage transformers. This fact motivated an R&D project in Brazil to study Fault Current Limiters for a utility. In this context, innovative design with a bifilar winding was developed for the present work, aiming to reduce self-inductance and to improve cooling rate. Long length second-generation superconducting tapes were used to build the prototype, which was constructed on a fiber-glass base. The prototype module has been tested at low voltage levels. The nominal operation, fault current limitation and recovery time have been examined for prospective currents of 2700 A and reduction of about 90 % in the current level. Due to fast recovery time and good heat exchange, the proposed topology has potential to be applied in a full-scale prototype.

Generic Model of Three-Phase (RE)BCO Resistive Superconducting Fault Current Limiters for Transient Analysis of Power Systems

This paper presents the modelling and implementation of a generic three-phase resistive superconducting fault current limiter (r-ScFCL) for transient analysis of ac power systems. The r-ScFCL consists of series-connected noninductive coils made of insulated commercially available (RE)BCO tapes operated in a liquid nitrogen bath, in parallel with a resistive shunt at room temperature. The model allows the prediction of the thermal and electrical behaviors of the device prior to, during, and after a fault. It was used to evaluate the impact of a three-phase r-ScFCL on the transient stability of a synchronous generator supplying an infinite bus through a step-up transformer and a transmission line. More specifically, the impact of the r-ScFCL design on fault current magnitude, device voltage, temperature, and recovery time was studied. For the chosen case study, the r-ScFCL did increase the stability of the power system. It was also found that parameters such as the length of the superconducting tapes, the number of tapes in parallel, and the shunt resistance can balance or unbalance the response of the r-ScFCL over the three phases during a fault.

Schottky Barrier Rectifier Based on (100) $\beta$ -Ga2O3 and its DC and AC Characteristics

A Schottky barrier rectifier was fabricated with a (100)-oriented $\beta $ -Ga2O3 substrate grown by the edge-defined film-fed method. The Sn-doped $\beta $ -Ga2O3 substrate had an effective donor concentration of approximately $2\times 10^{17}$ cm−3. High performance parameters were obtained, such as a high forward current (421 A/cm2 at 2 V), low ON-resistance (2.9 $\text{m}\Omega \cdot $ cm2), and short reverse recovery time (20 ns). Furthermore, the dynamic behavior of the device is characterized through test on the half-wave rectification of ac voltages at different frequency. The diode worked well at 100 kHz. At the end of the letter, we discuss how Ga2O3 Schottky rectifier can operate at high frequency.

Improvement of Operation Speed of LR-Biased Low-Power Single-Flux Quantum Circuits by Introduction of Dynamic Resetting of Bias Currents

We propose a new inductive- and resistive- (LR) biased low-power single-flux quantum (SFQ) circuit that has a dynamic resetting mechanism of the bias current. Because the bias current returns to the initial state rapidly by switching of a Josephson junction in the bias circuit after circuit operation, the operating frequency of the LR-biased SFQ circuit can be improved. We simulated a Josephson transmission line (JTL) that employs the proposed biasing scheme and evaluated the bias current recovery time. Circuit simulation results show that the bias current recovery time of the proposed circuit is improved by 10-20% compared to that of the conventional LR-biased JTL. We have designed and measured a 10-stage JTL and an 8-bit concurrent-flow shift register (SR) with the proposed biasing scheme. We have experimentally demonstrated operation of the JTL with the bias margin of ±29.4% at the operating frequency of up to 70.4 GHz and operation of the 8-bit SR up to 12.3 GHz by the on-chip high-speed test.

Effect of the interface on UV–vis–IR photodetection performance of PbS/ZnO nanocomposite photocatalysts

Two PbS/ZnO nanocomposites with the same Pb/Zn molar ratio of 1:12 and different PbS/ZnO interface were prepared by depositing PbS nanocrystals on nano ZnO with the reaction between Pb(NO3)2 and Na2S through changing the sequence of adding Pb(NO3)2 and Na2S to the nano ZnO suspension: (A) first adding Pb(NO3)2 followed by adding Na2S (denoted PbS/ZnO-A); (B) first adding Na2S followed by adding Pb(NO3)2 (denoted PbS/ZnO-B). The PbS/ZnO nanocomposites are characterized by XRD, BET, Raman, TEM, XPS, and UV–vis–IR. The characterizations indicate that PbS/ZnO-A has an interface of PbS nanocrystal closely contacted to ZnO nanocrystal while PbS/ZnO-B has an interface of a disordered layer between PbS nanocrystal and ZnO nanocrystal. It is found for the first time that the PbS/ZnO interface plays an important role in their photodetection performance. PbS/ZnO-A exhibits much higher photoresponse current and lower rise and recovery time than both PbS/ZnO-B and a mixture of nano PbS and ZnO with the same Pb/Zn molar ratio as PbS/ZnO-A for visible and near-infrared photodetection. PL and the impedance measurement in dark and irradiation reveal that the superior photodetection performance of PbS/ZnO-A over PbS/ZnO-B is attributed to its lower e–h recombination and migration resistance under the irradiation of visible and infrared light due to its very good PbS/ZnO interface of PbS nanocrystals closely attached ZnO nanocrystals, through which photogenerated electrons inject efficiently from the conduction band of PbS to that of ZnO. In contrast, the defect sites in the disordered layer between PbS nanocrystal and ZnO nanocrystal for PbS/ZnO-B act as e–h recombination centers, significantly decreasing the e–h separation efficiency.

Mitigation fault of node mobility for the MANET networks by constructing a backup path with loop free: enhance the recovery mechanism for pro-active MANET protocol

The performance implications of link or node failures in Mobile Ad-hoc Network (MANET) networks are studied in details. Several recovery mechanisms are proposed to reduce the impact of failure and guarantee a loop-free in the network. These mechanisms seek to reduce recovery time, which remains undesirably long in the current routing protocols in wired and wireless networks. Hence, we evaluate the efficiency of the Optimized Link State Routing Protocol with and without recovery paths under varying environment with different node densities. In addition, the mobility of nodes is changing the speed movements when they start to move from area to another one. This paper assists in ascertaining the effect of varying node densities on the connectivity's life between mobile nodes in the network. Hence, it showed the effect of a local recovery mechanism resulted in achieving a significant improvement in network performance by seeking a long life backup path between source and destination for different nodes density. Real time applications are required to be supported by mobile ad hoc networks by finding an efficient recovery mechanism. This is because the MANET networks allow the nodes to move from one area to another without any notification. The real time applications traffics are considered as a sensitive application, and it is the most affected by failure through the occurrence of delay and loss of packets. It is, therefore, not suitable for use by players. In mobile ad hoc networks, routing protocol functions are based on many factors, such as, node mobility and density and broken paths. According to these factors, the paper was further extended to develop a recovery mechanism in MANET based on the mobility and density of nodes to alleviate the impact of the frequent loss of connection due to the flexibility of free nodes, which move from one area to another without pre-notification. The aim behind recovery mechanism is to reduce current recovery time to enhance the Quality of Service in the MANET.

Effects of Gate Field Plates on the Surface State Related Current Collapse in AlGaN/GaN HEMTs

During off-state, the influence of surface-trapped electron charges induced by high-field stress near the gate electrode of AlGaN/GaN power high-electron mobility transistor devices causes a reduction in two-dimensional electron gas (2DEG) carrier density at the heterointerface. In a pulse turn-on operation, the weakened 2DEG channel results in a higher on-state conduction resistance during the transient, known as the current collapse phenomenon. The phenomenon increases the switching loss by a higher on-state resistance and prolonged turn-on transition time, thus limits the device operating frequency range. In this paper, such a phenomenon is modeled, analyzed by Sentaurus TCAD simulation, and verified by the laboratory measurement data, with the emphasis on the influence of field plates toward the current collapse. The spatial distributions of trapped electrons and excess free electrons along the AlGaN surface are modeled and analyzed to arrive at the quantitative relationships among the trapped electron density, on-resistance increase, and the electric field distribution which provide a reliable criterion for current collapse reduction. It was found that, with a proper field plate design, it is possible to achieve an improvement on transient on-state resistance and the current recovery time.

单根ZnO纳米线低温条件下的电子输运及光敏性质

ZnO nanowires were synthesized by chemical vapor deposition method,and single ZnO nanowire semiconductor devices with Ohmic contact electrodes were fabricated using the micro grid template method. The electrical properties of the device were investigated at low temperatures. The results show that there are two types of transport mechanism: thermal activation and nearest-neighbor hopping mechanism from 300 to 60 K. The properties of ultraviolet light response and recovery of the device were tested at 300,200,and 100 K,respectively. The results show that the sensitivity of the device to ultraviolet is improved at low temperature,and the current recovery time increases with the temperature falling down.

TRPV1 properties in thoracic dorsal root ganglia neurons are modulated by intraperitoneal capsaicin administration in the late phase of type-1 autoimmune diabetes.

Pharmacological therapies in type 1 diabetes for efficient control of glycemia and changes in pain alterations due to diabetic neuropathy are a continuous challenge. Transient receptor potential vanilloid type 1 (TRPV1) from dorsal root ganglia (DRG) neurons is one of the main pharmacological targets in diabetes, and its ligand capsaicin can be a promising compound for blood-glucose control. Our goal is to elucidate the effect of intraperitoneal (i.p.) capsaicin administration in type 1 diabetic mice against TRPV1 receptors from pancreatic DRG primary afferent neurons. A TCR(+/-)/Ins-HA(+/-) diabetic mice (dTg) was used, and patch-clamp and immunofluorescence microscopy measurements have been performed on thoracic T(9)-T(12) DRG neurons. Capsaicin (800 μg/kg, i.p. three successive days) administration in the late-phase diabetes reduces blood-glucose levels, partly reverses the TRPV1 current density and recovery time constant, without any effect on TRPV1 expression general pattern, in dTg mice. A TRPV1 hypoalgesia profile was observed in late-phase diabetes, which was partly reversed to normoalgesic profile upon capsaicin i.p. administration. According to the soma dimensions of the thoracic DRG neurons, a detailed analysis of the TRPV1 expression upon capsaicin i.p. treatment was done, and the proportion of large A-fiber neurons expressing TRPV1 increased in dTg capsaicin-treated mice. In conclusion, the benefits of low-dose capsaicin intraperitoneal treatment in late-phase type-1 diabetes should be further exploited.

Low-power fast-update pipelined phase accumulator for CML-based high-speed CMOS DDFSs

Presented is a phase accumulator (PACC) for current-mode logic (CML)-based high-speed CMOS direct digital frequency synthesisers (DDFSs). The proposed PACC not only consumes low power by using an adaptive power reduction technique, but also updates frequency information within one clock period by using dual function logic gates and the charge sharing scheme that accelerates current recovery time. This work reduces power consumption by 33% compared to the conventional PACC with a pipeline depth of 8 and 32-bit FCW.

Transient Electrical Characteristics of Electron Irradiated High Blocking Voltage 4H-SiC Pin Diode

The transient electrical characteristics of the forward recovery and reverse recovery characteristics of lifetime-controlled high blocking voltage 4H-SiC pin diodes by electron irradiation are investigated. Even at a heavy electron dose of 1×1014 cm-2, the forward voltage overshoot of a 4H-SiC pin diode is lower than that of a 2 kV/100 A class Si fast diode. As for the reverse recovery characteristics, small reverse recovery current and fast reverse recovery time are obtained by electron irradiation. The reduction ratio of recovery loss can therefore exceed the increase ratio of steady-state loss by electron irradiation.

Fabrication and ultraviolet photoresponse characteristics of ordered SnO x (x ≈ 0.87, 1.45, 2) nanopore films

Based on the porous anodic aluminum oxide templates, ordered SnOx nanopore films (approximately 150 nm thickness) with different x (x ≈ 0.87, 1.45, 2) have been successfully fabricated by direct current magnetron sputtering and oxidizing annealing. Due to the high specific surface area, this ordered nanopore films exhibit a great improvement in recovery time compared to thin films for ultraviolet (UV) detection. Especially, the ordered SnOx nanopore films with lower x reveal higher UV light sensitivity and shorter current recovery time, which was explained by the higher concentration of the oxygen vacancies in this SnOx films. This work presents a potential candidate material for UV light detector.PACS: 81.15.Cd, 81.40.Ef, 81.70.Jb, 85.60.Gz.

Superconducting fault current limiter application in a power-dense marine electrical system

Power-dense, low-voltage marine electrical systems have the potential for extremely high fault currents. Superconducting fault current limiters (SFCLs) have been of interest for many years and offer an effective method for reducing fault currents. This is very attractive in a marine vessel in terms of the benefits arising from reductions in switchgear rating (and consequently size, weight and cost) and damage at the point of fault. However, there are a number of issues that must be considered prior to installation of any SFCL device(s), particularly in the context of marine applications. Accordingly, this study analyses several such issues, including: location and resistance sizing of SFCLs; the potential effects of an SFCL on system voltage, power and frequency; and practical application issues such as the potential impact of transients such as transformer inrush. Simulations based upon an actual vessel are used to illustrate discussions and support assertions. It is shown that SFCLs, even with relatively small impedances, are highly effective at reducing prospective fault currents; the impact that higher resistance values has on fault current reduction and maintaining the system voltage for other non-faulted elements of the system is also presented and it is shown that higher resistance values are desirable in many cases. It is demonstrated that the exact nature of the SFCL application will depend significantly on the vessel's electrical topology, the fault current contribution of each of the generators, and the properties of the SFCL device, such as size, weight, critical current value and recovery time.