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A consecutive parameter extraction technique describes the fitting target related parameters for Insulated-gate bipolar transistor (IGBT) model. The IGBT model has been represented by a couple of simplified equivalent circuits. Using simulated data for a trench-type IGBT as reference the performance of compact model IGBT is compared to an IGBT macro model. Due to physics based modeling, parameter extraction with the compact model is fast. With very less extraction effort, the compact model fits the dc current and capacitance characteristics accurately. more...

Using two rigorous electromagnetic approaches, we study plasmon scattering in two-dimensional systems and show that plasmon amplification is possible in the presence of dc currents. Two scenarios are considered: plasmon scattering from an interface between different two-dimensional channels and plasmon reflection from electric contacts of arbitrary thickness. In each case, the effect of a dc current of the plasmon reflection and transmission coefficients and the plasmon power are both quantified. A resonant system is studied where plasmon roundtrip gain may exceed unity, showing the possibility of plasmon generation. more...

In the previous researches of hybrid magnet memory motors (HMMMs), the demagnetization characteristics of low-coercive-force (LCF) magnets have been already investigated extensively. Nevertheless, the possible irreversible demagnetization of high-coercive-force (HCF) magnets remains unexplored hitherto. In this paper, the demagnetization behaviour of HCF magnets in switched flux hybrid magnet memory machines (SF-HMMMs) accounting for the high-level current pulse is revealed and investigated. A simplified magnetic circuit model is built to illustrate when and how the DC current pulse poses the risk of irreversible demagnetization to the HCF magnets. Furthermore, the influences of temperature, DC current amplitude and HCF magnet thickness on the irreversible demagnetization effect of HCF magnets in the investigated SF-HMMM are analyzed based on finite-element (FE) analyses. The theoretical and FE results are experimentally verified by the tests on an SF-HMMM prototype. more...

Research finds both quasi-linear and nonlinear self-localized bullet modes can be created with DC current in a nano-gap spin Hall nano-oscillator.

It has been found experimentally that when dc current is passed through a circuit consisting of two superconductors connected in parallel and reaches its critical value in one of the circuit branches the current in the branches undergoes quasi-harmonic undamped oscillations. The mechanism resulting in the appearance of the self-oscillations is discussed. The characteristics of magnetic field freezing in a circuit with self-oscillating current are examined., Comment: 3 pages, 3 figures more...

The Polaris high intensity, medium resolution, time-of-flight neutron diffractometer at ISIS has been used in a real-time study to observe phase evolution in rods of melt-cast Bi1.6Pb0.4Sr2Ca3Cu4Oy in situ as they were recrystallized by passage of a dc current under a series of controlled atmospheres. Together with simultaneous measurement of current and resistance to facilitate control over sample heating, the experiment required visual monitoring of the sample during neutron diffraction data collection. This article describes the apparatus constructed to carry out these experiments, along with the necessary modifications made to Polaris and its control systems, and presents results which demonstrate the effectiveness of the technique. The results presented show that the initial appearance of the Bi-2201 phase occurred before hot zone formation. On formation of the hot zone, development of Bi-2212 took place at the expense of Bi-2201. Finally, passage of the zone saw the Bi-2212 redissolve and Bi-2201 re... more...

A calculation is presented for the phase-dependent dc current induced in a semiconductor superlattice by the simultaneous application of an ac field and its phase-shifted second harmonic. The dc current is a result of the Esaki–Tsu non-ohmicity of the superlattice for the case where it Bloch oscillates. The effect provides a tool for a determination of the relaxation time of the electrons. more...

If you know what you're doing and have suitable equipment, you can make a quantum dot, a tiny conducting region that contains anywhere from a handful to several thousand electrons. A number of experimenters have studied the electron transport properties of such dots. Now a group at Stanford University and the University of California, Santa Barbara, has made an open quantum dot, changed the shape of the system cyclically, and found that a finite current flows. This surprising effect requires quantum phase coherence and is observable only at a temperature low enough to preserve quantum phase. The effect was recently reported by Michael Switkes and Charles Marcus (Stanford), and Kenneth Campman and Arthur Gossard (UCSB). more...

Electric‐field domains in semi‐insulating GaAs:Cr are investigated both by imaging the locally induced birefringence using a transverse electro‐optic configuration and by measuring the dc current flowing through the crystal. It is shown that the formation of domains may be controlled by optical means. more...

Migration enhanced epitaxy (MEE) was used in this work to grow p+‐GaAs at the substrate temperature of 300 °C for the base of AlGaAs/GaAs heterojunction bipolar transistors. The results indicated that the low‐temperature MEE‐grown p+‐GaAs epitaxial layers (p=1×1019–1×1020 cm−3) exhibited a crystalline quality comparable to those grown by standard MBE at a substrate temperature of 570 °C. AlGaAs/GaAs HBTs with low‐temperature MEE‐grown bases doped at p≊2×1019 cm−3 were fabricated by using a self‐alignment technique. For the devices with the conventional MBE‐grown base, secondary ion mass spectroscopy depth profiles showed a significant Be diffusion into the AlGaAs emitter and as a consequence, the devices showed no current gain. For the devices with the low‐temperature MBE‐grown base, there was a negligible Be penetration into the emitter and the devices exhibited a common‐emitter dc current gain of 13. more...

A small laterally confined area of the two‐dimensional electron gas (2DEG) separated from two wide 2DEG regions by potential barriers is considered. Transparencies of the barriers can be controlled by the split gate voltages. The analysis shows that the dc current through the device can be quantized in units of ef, where f is frequency of the gate voltage modulation. more...

We experimentally and numerically investigated rf oscillation induced by spin transfer torque in a current-perpendicular-to-plane giant magnetoresistance (GMR) device with full-Heusler Co2MnSi (CMS) layers. High output power (Prf) of 1 nW was experimentally achieved owing to the large GMR effect resulting from the half-metallic feature of the CMS layers. However, the high power rf oscillation was observed only in the narrow dc current (Idc) region. Macrospin simulation suggested that the high spin polarization of CMS layers led to narrowing the optimum Idc region for the rf oscillation. more...

Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. The process typically uses moderate uni-axial pressures ( more...

The current-induced depinning of a domain wall from an artificial pinning site is investigated in Permalloy nanowires. The depinning probability exhibits an oscillatory dependence on the current pulse length, which is, surprisingly, reduced when a dc current of the same polarity is added to the current pulse. By contrast, the depinning probability increases when dc and pulsed currents have opposite polarities even though the total current flowing though the device is smaller. These results are understood within an analytical one-dimensional model of the domain wall dynamics. more...

We report the switching behavior of resistive states induced by current flowing in La1−xCaxMnO3 films. The transport behavior upon treatments by applying a large dc current has been investigated in the absence of magnetic field. A switching from low to high resistive state was found upon applying a large dc current for the both compositions. The critical currents for the switching are 10.5mA (density of 2.3×103A∕cm2) and 6.7mA (density of 1.6×103A∕cm2) for compositions x=0.2 and 0.3, respectively. Our repeated measurements indicate that the high resistive state appeared in the film x=0.2 is much stable. Exposing the sample in air and room temperature does not cause any change of the transport properties. However, for the film with x=0.3, the induced high resistive state behaves with unstable characteristics. Keeping the sample at a low temperature of 20K, a relaxation to a higher resistive state takes place. The mechanism of phase separation was taken into account in the interpretation of the observed phe... more...

In this paper, a mathematical model for the dc current of organic thin film transistors is proposed. The model is based on the variable range hopping transport theory, while the mathematical expression of the current is formulated by means of the channel accumulation charge. It accurately accounts for below-threshold, linear, and saturation operating conditions via a single formulation and it does not require the explicit definition of the threshold and saturation voltages. Furthermore, thanks to the charge control approach, it is straightforwardly generalizable to dynamic behavior. more...

We present low-temperature scanning electron microscopy (LTSEM) investigations of superconducting microbridges made from ultrathin NbN films as used for hot electron bolometers. LTSEM probes the thermal structure within the microbridges under various dc current bias conditions, either via electron-beam-induced generation of an unstable hotspot, or via the beam-induced growth of a stable hotspot. Such measurements reveal inhomogeneities on a micron scale, which may be due to spatial variations in the NbN film or film-interface properties. Comparison with model calculations for the stable hotspot regime confirm the basic features of common hot spot models., Comment: 3 pages, 3 figures more...

The temperature dependence of the switching current of a magnetic nanopillar is investigated from 10to290K. According to the switching probability measurement with the pulsed current, and the differential resistance measurement with sweeping the dc current, the intrinsic switching currents increase with decreasing the temperature. Transport calculations show that this temperature dependence is closely related to the reduced spin accumulation and spin polarization of the electrical current at low temperatures, attributed to the varied transport parameters. The conclusion is in accordance with the temperature dependence of the resistance difference between antiparallel and parallel magnetic configurations. more...

The sensitive depth of semiconductor radiation detectors is widely believed to be the depletion depth. Recent experiments, however, showed that the x‐ray response of surface‐barrier detectors is independent of the depletion depth when operated in dc current mode [K. W. Wenzel and R. D. Petrasso, Rev. Sci. Instrum. 59, 1380 (1988)]. We report experimental observation of such detectors in both current mode and pulse mode operations to alpha particles and to short‐pulsed x rays (0.1–1 μs). It demonstrates that the difference in sensitivity between the detector’s dc response and pulsed‐signal response is caused by the different charge collection time in depleted and undepleted regions. Therefore, the sensitive depth depends on how the detector is operated, and is not always the depletion depth. The construction and operation of the short‐pulsed x‐ray source is also described. This work was supported by the U.S. Department of Energy contract No. DE‐AC02‐78ET51013. more...

A self-balancing bridge system with a dc current comparator and a superconducting flux-gated galvanometer is described. The bridge is capable of measuring small resistances (10(-4)-10(-7) Omega) at liquid helium temperatures with an accuracy of 1 ppm. more...

New results are obtained on plasma column resonances subjected to a high‐frequency field for the case of high incident power. The resonance shift and hysteresis are measured with good accuracy. A theoretical model based on the energy balance of the electron gas is established. It is shown that the plasma is maintained in a resonant state by the high‐frequency (HF) power with or without dc current. A graphical method to determine the electron density variation due to the HF field is described. This method predicts correctly the resonance shift and the hysteresis. more...

Measurements of the dc current density at 77 °K lattice temperature vs electric field for 26‐Ω cm n Si are presented and analyzed to determine the amount of repopulation when the field is applied in the 〈100〉 and 〈110〉 crystallographic directions. A relatively simple and straight‐forward technique for computing the energy‐relaxation‐time dependence on the electric field is proposed and applied to n Si. The electron temperatures vs electric field for several differently oriented conduction‐band minima are also calculated. An explanation for the previously observed but unexplained decrease in amount of repopulation above 400 V/cm is given. A new technique for computing the theoretical repopulation‐field dependence is also presented and found to give excellent agreement with the experimental results. A theory similar to that used in past literature, but more general, is used in the following experimental determination of the warm‐carrier repopulation in n Si. more...

Numerical calculations utilizing a realistic carrier velocity vs electric field relationship have been carried out for the dc current‐voltage characteristics and small‐signal ac response of abrupt Si p+np+, p+nvp+, n+pn+, and n+pπn+ barrier injection transit time (BARITT) devices. The small‐signal ac response of these devices can be represented accurately by the depletion capacitance either in parallel with a negative conductance or in series with a negative resistance. The negative conductance has maximum amplitude for transit angles of approximately 1.55π and dc current density biases of 20–100 A/cm2. A distinct advantage was found in small‐signal applications for p+np+ devices over p+nvp+ devices and for n+pn+ devices over n+pπn+ devices. more...

The influence of external circuit parameters on the measured current‐voltage behavior of double barrier resonant tunneling structures is studied both experimentally and through modeling. It is demonstrated that characteristic ‘‘plateaulike’’ structures, which often appear in the region of negative differential resistance, can be accounted for in terms of the oscillating nature of the circuit, given that only average currents and voltages are monitored. more...

The emission linewidth of a Nb–Nb Josephson point contact is measured vs dc current and compared with the theoretical predictions of Stephen and Scalapino. The good agreement between experimental results and theory even for high junction currents, the pair current being generally much larger than the quasiparticle current, indicates that Stephen's theory gives a fair picture of the pair‐current noise properties in point‐contact junctions. more...

A new nondestructive method is reported to investigate electromigration‐induced void formation in aluminum stripes on silicon substrates. X‐ray topography and optical microscopy are employed to characterize void nucleation at or below the film surface. Results are presented to show the correlation between x‐ray and optical images of void structures in an aluminum stripe after dc current flow. more...

An inexpensive improved dc voltage supply for high‐vacuum straight through valves is described. The electronic circuit is composed of two parts: (1) the current generating section which withdraws the valve gate and maintains it in the open position and (2) the section which monitors whether the valve gate is open or closed. more...

By using a cryogenic current comparator with a ferromagnetic core, optimum matching for high‐source resistances of up to about 400 kΩ for a commercially available rf SQUID is achieved. This extends the use of SQUID instruments considerably, especially for applications where the source resistance exceeds 10−1 Ω. more...

An alternative method of measuring soft x‐ray appearance potential spectra is presented. In this method no modulation, tuned tank, or lock‐in amplifier are used. Rather, the dc current induced in a simple Park‐Houston type detector is measured and digitized, and the data are placed on paper tape for computer processing and differentiation. The computer differentiated spectra compare favorably with spectra obtained by modulation technique. more...