Excess Current Research Articles

Anomalous Scatter of Forward Current-Voltage Characteristics of He<sup>+</sup>-Irradiated Ni/4H-SiC Schottky Diodes

A study of forward current-voltage characteristics of Ni/4H-SiC Schottky diodes (SDs) before and after irradiation with He+ ions revealed features that characterize defect structures and reveal the degradation mechanism of the diodes. These features are the presence of excess currents of certain type in the unirradiated SDs, their appearance in forward-biased originally ideal SDs, and a >10 orders of magnitude scatter of the series resistance of the SDs upon their irradiation with He+ ions. A model of localized defect-induced current paths (shunts) in the form of unintentionally produced SDs with the substrate is suggested.

Excess current in ferromagnet-superconductor structures with fully polarized triplet component

We study the $I$-$V$ characteristics of S$_{\text{T}}$/n/N contacts, where S$_{\text{T}}$ is a BCS superconductor S with a built-in exchange field $h$, n represents a normal metal wire, and N---a normal metal reservoir. The superconductor S$_{\text{T}}$ is separated from the n-wire by a spin filter which allows the passage of electrons with a certain spin direction so that only fully polarized triplet Cooper pairs penetrate into the n-wire. We show that both the subgap conductance $\sigma_{\text{sg}}$ and the excess current $I_{\text{exc}}$, which occur in conventional S/n/N contacts due to Andreev reflection (AR), exist also in the considered system. In our case, they are caused by unconventional AR that is not accompanied by spin flip. The excess current $I_{\text{exc}}$ exists only if $h$ exceeds a certain magnitude $h_{\text{c}}$. At ${h < h_{\text{c}}}$ the excess current is converted into a deficit current $I_\text{{def}}$. The dependencies of the differential conductance and the current $I_{\text{exc}}$ are presented as a function of voltage and $h$.

Impact of Bias Conditions on Total Ionizing Dose Effects of &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{60}{\hbox{Co}}\gamma $&lt;/tex-math&gt; &lt;/inline-formula&gt; in SiGe HBT

The effect of bias condition on total ionizing dose (TID) of Silicon–Germanium heterojunction bipolar transistors (SiGe HBTs) is investigated. The SiGe HBTs are set at forward, saturated, cutoff, and all-grounded biases during $^{60}{\hbox{Co}}\gamma $ irradiation. After each irradiation stops, the forward Gummel characteristic and inverse Gummel characteristic are measured, and a 3-D simulation of TID for SiGe HBT is performed. The mechanism of TID in different bias conditions is obtained by analyzing normalized excess base current. The results show that the TID damages are different at various irradiation biases of the SiGe HBT, and the worst bias between forward and inverse Gummel characteristics exhibits inconsistently. The reason could be attributed to different defects produced and accumulated in oxide layers by irradiation at various bias conditions. To be specific, the oxide trap charges ( ${{\hbox{N}}_{\rm ot}}$ ) in emitter/base (E/B) Spacer is important to the forward Gummel characteristic, yet the ${{\hbox{N}}_{\rm ot}}$ in LOCOS determines the inverse Gummel characteristic. However, after long time irradiation, the interface states ( ${{\hbox{N}}_{\rm it}}$ ) both in E/B Spacer and LOCOS dominate the damage to the SiGe HBT despite in forward Gummel mode or inverse Gummel mode.

A comparison of lower and higher LET heavy ion irradiation effects on silicon NPN rf power transistors

The Silicon NPN rf power transistors were irradiated with 180MeV Au14+ and 150MeV Ag12+ ions in the dose range of 1Mrad to 100Mrad. The SRIM simulation was used to understand the energy loss and range of these ions in the transistor structure. The different electrical parameters such as Gummel characteristics, excess base current (∆IB), dc current gain (hFE), transconductance (gm), displacement damage factor (K) and output characteristics were studied systematically before and after irradiation. These results were compared with lower linear energy transfer (LET) ions such as 50MeV Li3+, 95MeV O7+, 100MeV F8+, 140MeV Si10+ and 175MeV Ni13+ ions in the same dose range. The degradation for 180MeV Au14+ and 150MeV Ag12+ ion irradiated transistors was significantly more when compared to lower LET ions, indicating that the transistors are vulnerable to higher LET ion irradiations. Isochronal annealing study was conducted on the irradiated transistors to analyze the recovery in different electrical parameters. After isochronal annealing, the recovery in hFE and other electrical parameters was around 67% for Ag12+ ion irradiated transistors and 60% for Au14+ ion irradiated transistors.

Total ionizing dose effects of domestic SiGe HBTs under different dose rates

The total ionizing radiation (TID) response of commercial NPN silicon germanium hetero-junction bipolar transistors (SiGe HBTs) produced domestically are investigated under dose rates of 800 mGy(Si)/s and 1.3 mGy(Si)/s with a Co-60 gamma irradiation source. The changes of transistor parameters such as Gummel characteristics, and excess base current before and after irradiation, are examined. The results of the experiments show that for the KT1151, the radiation damage is slightly different under the different dose rates after prolonged annealing, and shows a time dependent effect (TDE). For the KT9041, however, the degradations of low dose rate irradiation is higher than for the high dose rate, demonstrating that there is a potential enhanced low dose rate sensitivity (ELDRS) effect for the KT9041. The possible underlying physical mechanisms of the different dose rates responses induced by the gamma rays are discussed.

A Review on Development and Operational Strategy of Fault Current Limiters

Distributed Generation (DG) plays a major role in existing power system. When such distributed generation system is interconnected with micro-grid improves voltage profile, power quality but at the same time results in fault conditions. Among various faults occurring in the power system, short circuit faults are the most predominant case. This results in the increase in flow of the fault current in the line. Also the equipments installed in such a line get damaged internally due to flow of excess fault current. Therefore in order to improve the transient conditions and limit the fault current to a manageable level, a device called Fault Current Limiters (FCLs) are being used in recent trend. This paper reviews about various fault current limiters, their development, characteristics and operating performance in the system. It gives a detailed knowledge about various operations performed by fault current limiters that is compared with other conventional techniques.

Efficiency Improvement with Solid State Starter for Three Phase Induction Motor Applications

Three phase induction motor is a versatile machine for energy conversion. All three phase machine will operate with a starter. The Starter is a mechanical or electromechanical device. Starters are facilitating for easy on and off the motor, protect from excess load current, and safe from low or high supply voltage. Some of the starters have mechanism of reduce the starting input current to the motor. These are activated through mechanical or electromechanical components. The solid state starter eliminates the mechanical components action and working as static device. The a) moveable touch contactor, b) Thermal or magnetic overload relay, which through the load current flow, c) No volt coil, which is to be energized for plunger contactor are major components of the starter. The above components are consuming the power during the whole operational time of the motor. The solid state starter is minimizing the above power loss at great extent. The solid state starter activation speed also very high since the capture the voltage value, current value, temperature value and to and fro of control signals for operating the motor is based digital system. The applied voltage, load current, temperature of the motor are captured by sensors and fed to the PIC controller, and the star to delta conversion and power feed to the motor by activating GTO also implement by same PIC controller. This method of starting the motor has many advantageous such as reduce more loss and increase the efficiency, more reliability, effective sensitivity, compact size of the starter. The method of starting is executing with MATLAB simulation and physically verified as wellconfirmed.

Estimation results taste sensitivity in remote dates after prosthesis in patients with galvanism, the use of non-removable prosthetic devices

The paper presents results of investigation of non-removable dentures on the quality and level of taste sensations in patients with different levels of potential difference (the magnitude of galvanic currents) in the mouth, using non-removable dentures from 6 months to a year, and the estimated degree of operational deterioration of prostheses and its relationship with the value of galvanic currents and the degree of disturbance of taste sensitivity to sweet, salty and sour. It is shown that there is a statistically significant positive direct-time relationship between excess level galvanic currents in the mouth, increased destruction of prostheses and change of taste sensitivity to sour and salty.

Study of partial discharge activity by excess current

Measurements of partial discharges (PD) play an important role in study of dielectric materials. This work applies a measurement system based on dielectric response technique to study an excess current associated with PD activity, which appears during and after PD activity and shows some prominent properties. The value of such a measurement is demonstrated through studies of two types of test objects, twisted pairs and cavity specimens. A simultaneous use of pulse PD detection in the study shows a correlation between changes in PD amplitudes and non-PD excess current levels. It is concluded that the used methodology can serve as an important complement to the traditionally used pulse PD detection.

A Review on Development and Operational Strategy of Fault Current Limiters

&lt;p&gt;Distributed Generation (DG) plays a major role in existing power system. When such distributed generation system is interconnected with micro-grid improves voltage profile, power quality but at the same time results in fault conditions. Among various faults occurring in the power system, short circuit faults are the most predominant case. This results in the increase in flow of the fault current in the line. Also the equipments installed in such a line get damaged internally due to flow of excess fault current. Therefore in order to improve the transient conditions and limit the fault current to a manageable level, a device called Fault Current Limiters (FCLs) are being used in recent trend. This paper reviews about various fault current limiters, their development, characteristics and operating performance in the system. It gives a detailed knowledge about various operations performed by fault current limiters that is compared with other conventional techniques.&lt;/p&gt;

Defect and temperature dependence of tunneling in InAs/GaSb heterojunctions

We assess the origin of the reported temperature dependence of subthreshold slope in many published tunnel field effect transistors (TFETs) by examining the temperature dependence of the intrinsic tunneling at InAs/GaSb interfaces in the absence of three-terminal parasitics. We compare the temperature dependence of peak current, excess current, and conductance slope for interfaces with and without heavy interface defect concentrations. We identify that the tunnel and excess currents depend on temperature and defect density but that the conductance slope, a two-terminal analog to subthreshold slope, depends only on defect density and not temperature, contrasting sharply with the heavy temperature dependence seen in TFETs in literature. We propose that TFETs based on this and similar materials systems are dominated by parasitic effects such as tunneling into oxide trap states, or other parasitics that are not intrinsic to the heterojunction itself, and that in the absence of these effects, the true steepness from band-to-band tunneling is limited by defects and inhomogeneity at the interface.

Excess currents in planar Ba(FeCo)As/TiO/Pb Josephson junctions

AbstractWe prepared planar hybrid Josephson junctions using Co‐doped BaFeAs thin films and polished single crystals as base electrode, sputtered, and subsequently oxidized titanium layers as barrier and a counter electrode from evaporated lead. On all junctions, RCSJ‐like current–voltage characteristics could be observed. The obtained products at 4.2 K range up to 95V for thin film junctions and up to 1.15 mV for junctions on single crystals. For most of the junctions, an excess current with variable contribution to the total current could be observed. Unusual temperature dependencies are discussed for the critical and the excess currents, respectively. Investigations of the junctions under microwave irradiation were performed, therein Shapiro steps up to high orders and very clear modulations of the steps could be observed. Additionally, the origin of the excess current is discussed with respect to the microwave dependence. Furthermore, instead of a single junction, a network‐like modulation behavior of the critical current in magnetic fields was observed.

Investigation of traps in strained‐well InGaAs/GaAsSb quantum well photodiodes

InP-based strained-well InGaAs/GaAsSb quantum well photodiodes with non-zero net strain can be used to extend detection wavelengths well into the mid-infrared region. However, excess dark current due to defects in the structure can be a performance limiting factor in photodiodes of this type. In this reported work, both low-frequency noise spectroscopy and deep level transient spectroscopy were used to investigate traps in prototypical strained-well photodiode heterostructures. Two distinct traps were identified and their electrical and physical properties and distributions have been evaluated.

Intermetallic junction contribution to the CO electrooxidation on a Pt/Au electrode: the excess voltammetric current

The contribution of the intermetallic junction to the electrocatalytic activity of a Pt/Au electrode for the carbon monoxide oxidation reaction (COOR) in alkaline solution is evaluated on the basis of the excess voltammetric current. This contribution is measured on a new type of bimetallic electrode characterized by a large ratio between the total intermetallic perimeter and the electrode area. The results obtained demonstrate that Pt/Au heterojunction enhances the reaction rate in two potential regions. This improvement is explained on the basis of the spillover of the CO adatoms from one side of the intermetallic junction to the other.

Inelastic electron-phonon scattering and excess current in superconducting point contacts with a short coherence length

Nonlinear electrical effects in superconducting S-c-S contacts, including the spectroscopy of electron-phonon interactions (EPI) in these systems, and the recovery of the EPI function from experimental data are discussed. The effect of a magnetic field on the current-voltage characteristics (I-V curves) and their derivatives for ErNi2B2C point contacts (PC) with d ≥ ξ (where d is the diameter of the PC and ξ is the coherence length) is studied. It is found that in zero magnetic fields and in near-critical fields, when the size of the superconducting gap can be neglected, the position of the peaks in dV/dI coincides with the peaks in the Yanson EPI spectra. In low fields the peaks are shifted toward lower energies and in intermediate fields, the peaks split. For PC with diameters greater than or on the order of the coherence length, the relative size of the negative phonon contribution to the excess current is considerably greater than in ballistic contacts. This leads to substantial suppression of the high-frequency peaks in the spectra for the superconducting state. In order to recover the EPI function from these spectra it is necessary to correct their intensities at high energies. For “dirty” NbSe2 and Nb point-contacts with d ≥ ξ, which have no phonon features in the second derivative of the I-V curve in the normal state, the EPI can be reconstructed from the superconducting state.

Improved Model for Increased Surface Recombination Current in Irradiated Bipolar Junction Transistors

Current gain degradation in irradiated bipolar junction transistors is primarily due to excess base current caused by enhanced carrier recombination in the emitter-base space-charge region (SCR). Radiation-induced traps at the interface between silicon and the bipolar base oxide facilitate the recombination process primarily above the sensitive emitter-base junction. This leads to an increase in surface recombination current in the SCR, which is a non-ideal component of the BJT's base current characteristic under active bias conditions. In this paper, we derive a precise analytical model for surface recombination current that captures bias dependencies typically omitted from traditional models. This improved model is validated by comparisons to these traditional approaches.

Impact of defect on I(V) instabilities observed on Ti/4H–SiC high voltage Schottky diodes

Anomaly in current at low forward bias is observed for large-area Ti Schottky diodes on n type 4H–SiC. Random telegraph signal (RTS) measurements, carried out on these defective devices, show discrete time switching of the current. Thermal activation of RTS signal gives two related trap signature (activation energy and cross section). Frequency analysis, using power spectral densities (PSDs) numerically calculated, confirms the presence of an extended defect which presents different charge states (i.e. an extended defect decorated by punctual traps). PSDs show two cut-off frequencies proving the individual response of two traps. Simulations of the I–V characteristics using two barrier heights modulated by a Gaussian function which represents the defect distribution show a good agreement with the experimental results. Finally we note that there's a strong correlation between traps observed by telegraph noise techniques and excess current.

Characterization of 4H-SiC pn Structures with Unstable Excess Current

4H-SiC p+nn+ structures fabricated by implantation of Al into a commercial n-type 4H-SiC epitaxial layer doped to (3-5)Ÿ1015cm-3 have been studied. Structures with unstable excess forward current were characterized by electron beam induced current (EBIC) and secondary electron (SE) methods and by Auger-electron spectroscopy (AES). Numerous defects were found with a depth which exceed the thickness of the p+-layer. Also, it was demonstrated that the concentration of carbon on the SiC surface always exceeds that of silicon, which may be the reason for the initially unstable conductivity via the defects.

In-plane tunneling anisotropic magnetoresistance in (Ga,Mn)As/GaAs Esaki diodes in the regime of the excess current

We investigate the angular dependence of the tunneling anisotropic magnetoresistance in (Ga,Mn)As/n-GaAs spin Esaki diodes in the regime where the tunneling process is dominated by the excess current through midgap states in (Ga,Mn)As. We compare it to similar measurements performed in the regime of band-to-band tunneling. Whereas the latter show biaxial symmetry typical for magnetic anisotropy observed in (Ga,Mn)As samples, the former is dominated by uniaxial anisotropy along the 〈110〉 axes.

Optical Spectroscopic Analysis of ICP Nitridation for SIS Junctions With AlN Barriers

High quality, low-leakage superconductor-insulator-superconductor (SIS) junctions with Nb electrodes and aluminum oxide barriers are widely reported in the literature, and have become integral in the design and fabrication of various superconducting circuits. However, as current densities are increased, aluminum oxide based tunnel barriers show excess leakage currents due to defects and pinholes in the barrier layer. First reported by our group in 2007, AlN tunnel barriers grown via inductively coupled plasma (ICP) nitridation of Al overlayers are a promising alternative, producing low-leakage Nb/Al-AlN/Nb SIS junctions, with current densities in excess of 30 kA/cm 2 . A correlation between junction quality and plasma dissociation has been reported for Nb/Al-AlN/Nb junctions produced via an electron cyclotron resonance (ECR) plasma. In this work, a quantitative measure of the relative dissociation (RD) of an ICP is determined through the use of a commercially available Ocean Optics USB4000 Optical Spectrometer. The effects of various ICP parameters on the RD, and a correlation between the RD and quality of the resulting Nb/Al-AlN/Nb junctions are reported.