Excess Voltage Research Articles

Remote Plasma Device for Surface Modification at Atmospheric Pressure

Here, a novel atmospheric plasma device is presented, which applies the (remote) afterglow of micro-barrier discharges. The study evaluates its applicability to surface modification of temperature-sensitive particulates. As such, cylindrical samples have been placed in the remote treatment zone of the device, and the effects of treatment time and variable gas mixtures on the surface wettability are investigated. Furthermore, the influence of the excess voltage in He discharge with admixtures of O2, CO2 and N2 and the effect thereof on the water contact angle is described.

Elementary charge-transfer processes in mesoscopic conductors

We determine charge-transfer statistics in a quantum conductor driven by a time-dependent voltage and identify the elementary transport processes. At zero temperature unidirectional and bidirectional single-charge transfers occur. The unidirectional processes involve electrons injected from the source terminal due to excess dc bias voltage. The bidirectional processes involve electron-hole pairs created by time-dependent voltage bias. This interpretation is further supported by the charge-transfer statistics in a multiterminal beam-splitter geometry in which injected electrons and holes can be partitioned into different outgoing terminals. The probabilities of elementary processes can be probed by noise measurements: the unidirectional processes set the dc noise level, while bidirectional ones give rise to the excess noise. For ac voltage drive, the noise oscillates with increasing the driving amplitude. The decomposition of the noise into the contributions of elementary processes reveals the origin of these oscillations: the number of electron-hole pairs generated per cycle increases with increasing the amplitude. The decomposition of the noise into elementary processes is studied for different time-dependent voltages. The method we use is also suitable for systematic calculation of higher-order current correlators at finite temperature. We obtain current noise power and the third cumulant in the presence of time-dependent voltage drive. The charge-transfer statistics at finite temperature can be interpreted in terms of multiple-charge transfers with probabilities which depend on energy and temperature.

12-kV p-Channel IGBTs With Low On-Resistance in 4H-SiC

SiC bipolar devices are favored over SiC unipolar devices for applications requiring breakdown voltage in excess of 10 kV. We have designed and fabricated p-channel insulated-gate bipolar transistors (IGBTs) in 4H-SiC with 12-kV blocking voltage for high-power applications. A differential on-resistance of 18.6 mOmega ldr cm2 was achieved with a gate bias of 16 V, corresponding to a forward voltage drop of 5.3 V at 100 A/cm2, indicating strong conductivity modulation in the p-type drift region. A moderately doped current enhancement layer grown on the lightly doped drift layer effectively reduces the JFET resistance while maintaining a high carrier lifetime for conductivity modulation. The p-channel IGBT (p-IGBT) exhibits a transconductance that is 3times higher than that of the 12-kV n-channel SiC IGBTs. An inductive switching test was done at 1.5 kV and 0.55 A (~440 A/cm2) for the p-IGBTs, and a turn-on time of 40 ns and a turn-off time of ~2.8 mus were measured.

A simple method to characterize the afterpulsing effect in single photon avalanche photodiode

A simple method is introduced for studying the afterpulsing effect in InGaAs single photon avalanche photodiode. The afterpulsing probability is obtained through measuring the detection efficiencies of various biasing pulses, while the incident photons are kept constant. The effect of excess bias and temperature on the afterpulsing probability is investigated. When the device temperature is higher than 170 K, the afterpulsing probability is lower than 5% for all excess bias voltages because the trapped carrier lifetime is much shorter than the repetition period.

High‐efficiency GaN HEMTs on 3‐inch semi‐insulating SiC substrates

AbstractWe report on device performance and reliability of our 3″ GaN high electron mobility transistor (HEMT) technology. AlGaN/GaN HEMT structures are grown on semi‐insulating SiC substrates by metal‐organic chemical vapor deposition (MOCVD) with sheet resistance uniformities better than 2%. Device fabrication is performed using standard processing techniques involving both e‐beam and stepper lithography. AlGaN/GaN HEMTs demonstrate excellent high‐voltage stability and large efficiencies. Devices with 0.5 µm gate length exhibit two‐terminal gate‐drain breakdown voltages in excess of 160 V and drain currents well below 1 mA/mm when biased at 80 V drain bias under pinch‐off conditions. Load‐pull measurements at 2 GHz return both a linear relationship between drain bias voltage and output power as well as power added efficiencies beyond 55% up to 72 V drain bias for which an output power density of 9 W/mm with 25 dB linear gain is obtained. Reliability tests indicate a promising device stability under both radio frequency (RF) and direct current (DC) stress conditions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Phase slips in mesoscopic superconducting triangles

Voltage–current (V(I)) characteristics are investigated in the superconducting state of an equilateral triangle of 2.2μm2 area. Several steps in the V(I) curves indicate the presence of phase slip centers in the triangle. The field dependence of these steps follows the Little-Parks oscillations of the phase boundary, associated with the change of vorticity. The influence of the contacts manifests itself as an excess voltage and a negative differential resistance. In addition we show that the position of the current contacts modify the superconducting phase boundary measurements.

Unlocking diamond's potential as an electronic material

In this paper, we review the suitability of diamond as a semiconductor material for high-performance electronic applications. The current status of the manufacture of synthetic diamond is reviewed and assessed. In particular, we consider the quality of intrinsic material now available and the challenges in making doped structures suitable for practical devices. Two practical applications are considered in detail. First, the development of high-voltage switches capable of switching voltages in excess of 10 kV. Second, the development of diamond MESFETs for high-frequency and high-power applications. Here device data are reported showing a current density of more than 30 mA mm(-1) along with small-signal RF measurements demonstrating gigahertz operation. We conclude by considering the remaining challenges which will need to be overcome if commercially attractive diamond electronic devices are to be manufactured.

Polymer Composite Varistor

A reusable nonlinear polymeric composite varistor composed of a linear low density polyethylene (LLDPE) as the matrix and doped zinc oxide varistor powders as the functional fillers, sintered at 850, 950 and 1100℃ for 5 h, is used as a novel material to limit excess voltage, current or power. The functional fillers act as varistors due to their grain boundary characteristics which can be adjusted by different formula and sintering conditions. When applied field is above breakdown field of the filler the current density increases abrupt if a critical temperature is reached. Thereby the over voltage is limited by fillers (i.e. varistor effect) and the over current is limited by polymer matrix (i.e. PTC effect). We studied the dependence of the E-J characteristics on the preparation conditions of filler material, the filler content in the polymeric matrix and suggest possible nonlinear electrical-thermal switching mechanism.

Design and Analysis of a Dual-Step Field-Plate Terminated 4H-SiC Schottky Diode Using SiO<sub>2</sub>/High-K Dielectric Stack

Silicon carbide (SiC) field plate terminated Schottky diodes using silicon dioxide (Si02) dielectric experience high electric field in the insulator and premature dielectric breakdown, attributed to the lower dielectric constant of the oxide. This problem can be addressed by using high-k dielectrics such as silicon nitride (Si3N4) that will reduce the field, increase the breakdown voltage and consequently improve the lifetime of the devices. While the advantages of single step field-plate terminated diodes are well-known, the breakdown voltage can be improved even further using a dual-step field-plate termination. Our 2D-numerical simulations using MEDICI have shown an improvement in breakdown voltages in excess of 25% compared to the traditional single-step field-plate terminated diodes.

Deposition of single-phase CuIn(Se,S)2 thin films from the sulfurization of selenized CuIn alloys

The reaction of dc sputtered metallic CuIn alloys to a reactive H2Se/Ar/H2S gaseous atmosphere is an attractive industrial production process to produce CuIn(Se,S)2 chalcopyrite absorber films for applications in photovoltaic modules. However, the obvious technological advantages of this deposition technology are overshadowed by growth-related anomalies such as the separation or at least partial separation of the ternary phases (i.e. CuInSe2 and CuInS2) during the high temperature selenization/sulphurization of the metallic alloy. This in turn prevents the effective band gap widening of the semiconductor alloys in order to achieve open-circuit voltages in excess of 600 mV, which is a critical prerequisite for the optimal performance of thin film solar modules. In this contribution, the material properties of homogeneous single-phase CuIn(Se,S)2 alloys are discussed, produced with a novel two-stage deposition process.

Andreev spectroscopy of point contacts between a low-temperature superconductor and manganite

Andreev reflection in contacts between a low-temperature superconductor (Pb or MgB2) and the manganite La0.65Ca0.35MnO3 (LCMO) is investigated. In the majority of cases behavior typical of superconductor/half-metallic ferromagnet contacts is observed: an excess voltage Vexc and suppression of the contact conductance G(V)=dI(V)∕dV in the region of voltages e∣V∣≤ΔS, where ΔS is the energy gap of the injector. However, some of the contacts demonstrate an increase of the conductance and an excess current Iexc on the current–voltage characteristic of the contact at e∣V∣≤ΔS. The character of the dI(V)∕dV curves observed for those contacts corresponds to Andreev spectrum of a superconductor with an energy gap much larger than the injector gap ΔS. It is assumed that in contacts of the latter type, specific conditions prevail whereby the penetration of Cooper pairs into the manganite from an electrode with a singlet order parameter induces in the surface region of the manganite a superconducting state with a triplet type of correlations.

Ga In P ∕ Ga As double heterojunction bipolar transistor with GaAs∕Al0.11Ga0.89As∕GaInP composite collector

Ga In P ∕ Ga As ∕ Ga In P double heterojunction bipolar transistor (DHBT) with an Al0.11Ga0.89As layer within lowly doped GaAs–GaInP composite collector was characterized. In comparison to an abrupt GaInP∕GaAs∕GaInP DHBT with saturation voltages in excess of 20V, current gains of 25 at high biases, and breakdown voltages in the range of 22V, the DHBT incorporating GaAs–Al0.11Ga0.89As–GaInP composite collector has demonstrated lower saturation voltages of less than 6V and high current gains of 50 without compromising the breakdown voltages of the GaInP collector. Al0.11Ga0.89As layer can thus provide an alternative design to effectively minimize the potential spike effects at the GaAs∕GaInP heterojunction.

A fast driver circuit for single-photon sensors

A fast active quenching and recharging circuit (AQRC) for single-photon avalanche diodes (SPAD) is presented in this paper. The proposed driver exhibits a lower than 10ns overall quenching time allowing a tunable excess voltage from 5 to 12V. The circuit was designed by using the dielectrically insulated BiCMOS technology supplied by ST Microelectronics. Many post-layout ELDO simulations have validated the high performance of the proposed topology, which is actually the fastest AQRC reported in the literature.

Nano-ionics in the context of lithium batteries

In this paper, we highlight the field of nano-ionics which in contrast to the well established field of nano-electronics is still in status nascendi. We present some of our recent findings of different physical phenomena in the field of nano-ionics with special emphasis in the context of lithium batteries, addressing the following anomalies in various properties: (a) enhanced storage, Coulombic efficiency and excess storage at low potential due to interfacial insertion reaction, (b) thermodynamic aspects giving rise to excess cell voltage and curved shapes instead of plateau regions during multiphase co-existence and (c) transport behavior in a new class of soft matter electrolytes that combines high ionic conductivities at room temperature with the favorable properties of ‘soft matter’. Thus we emphasise here that the nano-ionics is relevant not only for fundamental science, but also important for technological applications.

Characterization of a CMOS Geiger photodiode pixel

This paper examines the performance of CMOS avalanche photodiode pixels operated in a Geiger mode. The pixels, called Geiger photodiode (GPD) pixels, convert an incident analog photon flux into a digital count rate. The maximum detection efficiency of the characterized GPD pixel for 632-nm light is 22%. The passively quenched GPD pixel exhibits an after pulsing at excess bias voltages above 2 V, and a minimum in the after-pulsing correction factor, of 0.53, occurs at an excess bias of 5.8 V. The after pulsing increases the fluctuations, or noise, in the count-rate signal. The following expression accurately describes the noise in the characterized GPD pixel, which exhibits a relatively low after-pulsing probability: /spl sigma//sup 2/=n~/sub dp/+n~/sub ap/+2/spl middot/[n~/sub dp//spl middot/n~/sub ap/]/sup 1/2/, where /spl sigma/ represents the count-rate fluctuations, the "dp" subscript stands for "detected photons," the "ap" subscript stands for "after pulses," and the n~ represents the "average count rate of" dp, or ap. The noise-equivalent illumination exhibits a minimum of 300 Hz at an operating voltage of 28 V. The best operating voltage for the GPD pixel increases from 28 V with increasing signal intensity.

Manufacturable MEMS miniSEMs

We present here the latest results of our manufacturable miniature scanning electron microscope (miniSEM) development effort that incorporates a micro-electro-mechanical-systems (MEMS) electrostatic microcolumn and a carbon nanotube (CNT) emitter. The microcolumn is designed for a beam diameter of 10–20 nm at the sample with beam energy of 1 keV at currents of up to 1 nA and a 100 μm field of view (FOV). The microcolumn components are fabricated on a single 50 μm thick silicon on insulator (SOI) wafer and are assembled to the pre-fabricated, self-aligning sockets to realize an inexpensive and compact microcolumn. A new MEMS process presented here allows the microcolumn electrodes to withstand voltages in excess of ±1 kV which is the maximum design voltage for any electrode. We also present measured electron optic characteristics of an Einzel lens and an octupole deflector along with simulations. The operational testing of the entire microcolumn is currently in progress.

Dual junction GaInP/GaAs solar cells grown on metamorphic SiGe/Si substrates with high open circuit voltage

Dual junction GaInP/GaAs solar cells have been grown and fabricated on Si substrates using relaxed, compositionally graded SiGe buffer layers that provide a nearly lattice-matched low threading dislocation Ge surface for subsequent cell growth. The dual junction cells on SiGe/Si displayed high open circuit voltages in excess of 2.2 V, compared to 2.34 V for control cells on GaAs, that are consistent with maintaining the 1.8/spl times/10/sup 6/ cm/sup -2/ threading dislocation density throughout the cell structure. Even with total current output limited by large grid coverage and high reflectance, total area AM1.5G efficiency is 16.8%, with active area efficiency at 18.6%. The high V/sub oc/ establishes that SiGe metamorphic buffers are viable for integrating III-V multijunction cells on Si in a monolithic process.

Disruption of extended defects in solid oxide fuel cell anodes for methane oxidation

Point defects largely govern the electrochemical properties of oxides: at low defect concentrations, conductivity increases with concentration; however, at higher concentrations, defect-defect interactions start to dominate. Thus, in searching for electrochemically active materials for fuel cell anodes, high defect concentration is generally avoided. Here we describe an oxide anode formed from lanthanum-substituted strontium titanate (La-SrTiO3) in which we control the oxygen stoichiometry in order to break down the extended defect intergrowth regions and create phases with considerable disordered oxygen defects. We substitute Ti in these phases with Ga and Mn to induce redox activity and allow more flexible coordination. The material demonstrates impressive fuel cell performance using wet hydrogen at 950 degrees C. It is also important for fuel cell technology to achieve efficient electrode operation with different hydrocarbon fuels, although such fuels are more demanding than pure hydrogen. The best anode materials to date--Ni-YSZ (yttria-stabilized zirconia) cermets--suffer some disadvantages related to low tolerance to sulphur, carbon build-up when using hydrocarbon fuels (though device modifications and lower temperature operation can avoid this) and volume instability on redox cycling. Our anode material is very active for methane oxidation at high temperatures, with open circuit voltages in excess of 1.2 V. The materials design concept that we use here could lead to devices that enable more-efficient energy extraction from fossil fuels and carbon-neutral fuels.

An investigation of excess noise in transition-edge sensors on a solid silicon substrate

Transition-edge sensors (TESs) exhibit two major types of excess noise above the expected and unavoidable thermodynamic fluctuation noise (TFN) to the heat sink and Johnson noise. High-resistance TESs such as those made by the Netherlands Institute for Space Research (SRON) show excess noise consistent with internal TFN (ITFN) caused by random energy transport within the TES itself while low resistance TESs show an excess voltage noise of unknown origin seemingly unrelated to temperature fluctuations. Running a high-resistance TES on a high thermal conductivity substrate should suppress ITFN and allow detection of any excess voltage noise. We tested two TESs on a solid silicon substrate fabricated by SRON of a relatively high normal state resistance of ∼200 mΩ. After determining a linear model of the TES response to noise for the devices, we found little excess TFN and little excess voltage noise for bias currents of up to ∼20 μA.

Information-theoretic criterion for the performance of single-photon avalanche photodiodes

A channel-capacity metric is introduced for assessing the performance of single-photon avalanche photodiodes (SPADs) when used as detectors in laser communication systems. This metric is employed to theoretically optimize, with respect to the device structure and operating voltage, the performance of SPADs with simple InP or In/sub 0.52/Al/sub 0.48/As-InP heterojunction multiplication regions. As the multiplication-region width increases, an increase is predicted in both the peak and the full-width at half-maximum of the channel capacity curve versus the normalized excess voltage. Calculations also show the existence of an optimal In/sub 0.52/Al/sub 0.48/As-InP heterojunction multiplication region that maximizes the peak channel capacity beyond that of InP.