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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

High voltage switch with cascaded transistor topology

A switching apparatus includes three or more series-connected transistors, and it further includes a balancing network. The balancing network includes a resistor network configured to divide a voltage from a voltage source across the series-connected transistors. The resistor network includes at least two resistive legs connected in parallel. In each resistive leg, two or more resistors are connected in series. The balancing network may further comprise at least one capacitive leg of series-connected capacitors connected across the series-connected transistors, and it may further comprise at least one leg of series-connected avalanche diodes connected across the series-connected transistors for overvoltage protection. In example embodiments, the series-connected transistors are JFETs. In other example embodiments, the series-connected transistors may be HEMTs or GaN transistors.

Gill, Lee↗
DOE OSTI2021

Current-Source Solid-State DC Transformer Integrating LVDC Microgrid, Energy Storage, and Renewable Energy Into MVDC Grid

Solid-state DC transformer to integrate low-voltage DC (LVDC) microgrid, wind turbine (WT) generator, photovoltaic (PV), and energy storage (ES) into medium-voltage (MV) direct-current (MVDC) distribution grids is attractive. This paper proposes current-source DC solid-state transformer (SST) for MVDC collection system in WT, PV, and ES farms or as an interface between the MVDC grid and the LVDC microgrid. Compared to conventional current-source converter (CSC) based SSTs, a switch reduction scheme on reverse-blocking device bridges is proposed to reduce device count and the number of devices on the DC-link current path. Importantly, the proposed switch reduction scheme is generic and can be applied to the DC ports of DC-AC, AC-DC, or DC-DC hard-switching or soft-switching CSC-based SSTs. Based on this scheme, the proposed current-source DC SSTs are derived, which have reduced electrolytic-capacitor-less DC-link. The proposed DC SSTs also achieve single-stage isolated DC-DC or DC-AC conversion, full-range zero-voltage switching (ZVS) for main switches, zero-current switching (ZCS) for resonant switches, and controlled dv/dt. The proposed DC SSTs, operating principles, predictive control method, the ZVS, and the controlled dv/dt under voltage buck-boost ranges are verified with MV simulations and an experimental prototype based on SiC MOSFETs, diodes, and a nanocrystalline transformer.

14 SOLAR ENERGY↗
DOE OSTI2021

Dimming LED circuit augmenting DC/DC controller integrated circuit

Embodiments include systems, methods, and apparatuses for providing a dimming function in a single stage AC input light emitting diode (LED) driver with a controller that contains an on-chip error amplifier and an on-chip fixed reference voltage source coupled to a first input of the error amplifier. The controller controls a duty cycle of a switching transistor to cause a feedback voltage, applied to a first package input terminal, to match the reference voltage. To achieve a dimming function, a voltage across a current sense resistor in series with the LEDs is applied to a first input of a high gain differential amplifier, and a variable dimming control voltage is applied to a second input of the differential amplifier. The output of the differential amplifier is coupled to the first package input terminal. The differential amplifier input signals will be matched at the target LED current level.

Song, Zhengrong↗
DOE OSTI2022

Charge Transport Characteristics of Molecular Electronic Junctions Studied by Transition Voltage Spectroscopy

The field of molecular electronics is prompted by tremendous opportunities for using a single-molecule and molecular monolayers as active components in integrated circuits. Until now, a wide range of molecular devices exhibiting characteristic functions, such as diodes, transistors, switches, and memory, have been demonstrated. However, a full understanding of the crucial factors that affect charge transport through molecular electronic junctions should yet be accomplished. Remarkably, recent advances in transition voltage spectroscopy (TVS) elucidate that it can provide key quantities for probing the transport characteristics of the junctions, including, for example, the position of the frontier molecular orbital energy relative to the electrode Fermi level and the strength of the molecule–electrode interactions. These parameters are known to be highly associated with charge transport behaviors in molecular systems and can then be used in the design of molecule-based devices with rationally tuned electronic properties. This article highlights the fundamental principle of TVS and then demonstrates its major applications to study the charge transport properties of molecular electronic junctions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Reverse-Bias Resilience of Monolithic Perovskite/Silicon Tandem Solar Cells

Metal halide perovskites have rapidly enabled a range of high-performance photovoltaic technologies. However, catastrophic failure under reverse voltage bias poses a roadblock for their commercialization. In this work, we conduct a series of stress tests to compare the reverse-bias stability of perovskite single-junction, silicon single-junction, and monolithic perovskite/silicon tandem solar cells. We demonstrate that the tested perovskite/silicon tandem devices are considerably more resilient against reverse bias compared with perovskite single-junction devices. The origin of such improved stability stems from the low reverse-bias diode current of the silicon subcell. This translates to dropping most of the voltage over the silicon subcell, where such a favorable voltage distribution protects the perovskite subcell from reverse-bias-induced degradation. These results highlight that, compared with other perovskite technologies, monolithic perovskite/silicon tandems are at a higher technology readiness level in terms of tackling the reverse bias and partial shading challenges, which is a considerable advantage toward commercialization.

halide perovskite↗
DOE OSTI2024

Spectroscopic performance of Low-Gain Avalanche Diodes for different types of radiation

LGADs (Low-Gain Avalanche Diodes or Detectors) are a type of silicon Avalanche Photo-Diodes originally developed for the fast detection of minimum ionizing particles in high-energy physics experiments. Thanks to their fast timing performance, the LGAD paradigm enables detectors to accurately measure minimum ionizing particles with a timing resolution of a few tens of picoseconds. Such a performance is due to a thin substrate and the presence of a moderate signal gain. This internal gain of a few tens is enough to compensate for the reduced charge deposition in the thinner substrate and the noise of fast read-out systems. While LGADs are optimized for the detection of minimum ionizing particles for high-energy particle detectors, it is critical to study their performance for the detection of different types of particle, such as X-rays, gamma-rays, or alphas. In this paper, we evaluate the gain of three types of LGADs: two devices with different geometries and doping profiles fabricated by Brookhaven National Laboratory, and one fabricated by Hamamatsu Photonics with a different process. Since the gain in LGADs depends on the bias voltage applied to the sensor, pulse-height spectra have been acquired for bias voltages spanning from the depletion voltage up to the breakdown voltage. Finally, the signal-to-noise ratio of the generated signals and the shape of their spectra allow us to probe the underlying physics of the multiplication process.

47 OTHER INSTRUMENTATION↗
NASA NTRS1992

Optically stimulated electron emission - Current-voltage response and spectral sensitivity

A highly reproducible optically stimulated electron emission (OSEE) response steel was achieved in laboratory conditions through suppression of surface photochemistry by replacing air with argon. This permitted the characterization of the OSEE process on D6AC steel as a photodiode. With a low-pressure mercury light source, most of the OSEE current is attributed to photoelectrons released by the 185-nm mercury line with only about 5 percent of the photocurrent associated with the 254-nm line. The forward current-voltage characteristic of the OSEE diode is linear for small fields changing to a square root response at larger fields. These results are all consistent with established theories.

Welch, Christopher S.↗
DOE OSTI2025

Exploring transport mechanisms in atomic precision advanced manufacturing enabled pn junctions

We investigate the different transport mechanisms that can occur in pn junction devices made using atomic precision advanced manufacturing at temperatures ranging from cryogenic to room temperature. We first elucidate the potential cause of the anomalous behavior observed in the forward-bias response of these devices in recent cryogenic temperature measurements, which deviates from the theoretical response of a silicon Esaki diode. These anomalous behaviors include current suppression at low voltages in the forward-bias response and a much lower valley voltage at cryogenic temperatures than theoretically expected for a silicon diode. To investigate the potential causes of these anomalies, we studied the effects of a few possible transport mechanisms, including band-to-band tunneling, bandgap narrowing, potential impact of non-Ohmic contacts, band quantization, impact of leakage, and inelastic trap-assisted tunneling, through semi-classical simulations. We find that a combination of two sets of band-to-band tunneling (BTBT) parameters can qualitatively approximate the shape of the tunneling current at low bias. This can arise from band quantization and realignment due to the strong potential confinement in δ-layers. We also find that the lower-than-theoretically-expected valley voltage can be attributed to modifications in the electronic band structure within the δ-layer regions, leading to a significant bandgap narrowing induced by the high density of dopants. Finally, we extend our analyses to room temperature operation and predict that trap-assisted tunneling (TAT) facilitated by phonon interactions may become significant, leading to a complex superposition of BTBT and TAT transport mechanisms in the electrical measurements.

band gap↗
DOE OSTI2021

Highly Integrated Wide Bandgap Power Module for Next Generation Plug-In Vehicles (Final Report)

Wide bandgap devices are key enablers for high power density traction inverters. A highly integrated wide bandgap (WBG) power module enables higher temperature operation, higher inverter efficiency and overall smaller die area with the same power delivery. However, it requires careful design of the power module to take advantage of all the superior material properties that silicon carbide (SiC) provides over conventional silicon (Si) Insulated Gate Bipolar Transistor (IGBT) based design. This project developed an efficient and densely packed SiC power module for an automotive traction inverter application. Extensive study was performed to select the best performing SiC die considering a wide range of temperature variation, suitability to integrate into target packaging, robust body diode performance and overall high electrical efficiency. Multiple design ideas were explored to achieve lower stray inductance for both power loop and signal loop, uniform current distribution, compact form factor, and very high thermal performance. The final power module package includes all six inverter switches in the same module (six-pack) with die sintered at both bottom and top surfaces utilizing high performance substrate to achieve high electrical and thermal performance. Two power module variants were developed using 900 V and 1200 V devices for operating at two different high voltage levels (> 600 V HV battery). Both power modules were comprehensively characterized, and high efficiency operation of the inverter was confirmed through analysis. Finally, a complete functional inverter was built with the 1200V power modules using other essential components (HV capacitors, gate driver board, controller board, current sensor, connectors etc.) and tested using GM’s standard test procedure. There are several challenges associated with adopting WBG devices for high voltage operation. In order to assess and mitigate those challenges, GM and subrecipients of this project have conducted multiple detailed studies. This includes phase current reconstruction using integrated Rogowski coil, device junction temperature estimation using on-state gate resistance, modeling and testing the effect of high voltage and fast switching on motor insulation and bearings, partial discharge inception voltage measurement under different environmental conditions. Findings of all these studies are summarized in this report.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS2001

InP MMIC Chip Set for Power Sources Covering 80-170 GHz

We will present a Monolithic Millimeter-wave Integrated Circuit (MMIC) chip set which provides high output-power sources for driving diode frequency multipliers into the terahertz range. The chip set was fabricated at HRL Laboratories using a 0.1-micrometer gate-length InAlAs/InGaAs/InP high electron mobility transistor (HEMT) process, and features transistors with an f(sub max) above 600 GHz. The HRL InP HEMT process has already demonstrated amplifiers in the 60-200 GHz range. In this paper, these high frequency HEMTs form the basis for power sources up to 170 GHz. A number of state-of-the-art InP HEMT MMICs will be presented. These include voltage-controlled and fixed-tuned oscillators, power amplifiers, and an active doubler. We will first discuss an 80 GHz voltage-controlled oscillator with 5 GHz of tunability and at least 17 mW of output power, as well as a 120 GHz oscillator providing 7 mW of output power. In addition, we will present results of a power amplifier which covers the full WRIO waveguide band (75-110 GHz), and provides 40-50 mW of output power. Furthermore, we will present an active doubler at 164 GHz providing 8% bandwidth, 3 mW of output power, and an unprecedented 2 dB of conversion loss for an InP HEMT MMIC at this frequency. Finally, we will demonstrate a power amplifier to cover 140-170 GHz with 15-25 mW of output power and 8 dB gain. These components can form a power source in the 155-165 GHz range by cascading the 80 GHz oscillator, W-band power amplifier, 164 GHz active doubler and final 140-170 GHz power amplifier for a stable, compact local oscillator subsystem, which could be used for atmospheric science or astrophysics radiometers.

Ngo, Catherine↗
DOE OSTI2020

Study of CMOS strip sensor for future silicon tracker

Monolithic silicon sensors developed with High-Voltage CMOS (HV-CMOS) processes have become highly attractive for charged particle tracking. Compared with the standard CMOS sensors, HV-CMOS sensors can provide larger and deeper depletion regions that lead to larger signals and faster charge collection. They can provide high position resolution, low material budget, high radiation hardness and low cost that are desirable for high performance tracking in harsh collision environment. Various studies have been conducted to explore the technology feasibility for the large-area tracking systems at future collider experiments. CHESS (CMOS HV/HR Evaluation for Strip Sensor) sensor series have been developed as an alternative solution to the conventional silicon micro-strip detectors for the ATLAS inner tracker upgrade. The first prototype (named CHESS1) was to evaluate the diode geometry and the in-pixel analog electronics. Obtained test results were used to optimize the second prototype (named CHESS2). CHESS2 was implemented with a full digital readout architecture and realized as a full reticle sized monolithic sensor. Here, the basic characteristics of the CHESS2 prototype sensors and their performance in response to different input signals are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1980

Deep-level defects and recombination parameters in proton irradiated AlGaAs-GaAs solar cells

The deep-level defects produced in high efficiency AlGaAs-GaAs solar cells by proton energies of 50, 100, 200, and 290 keV are investigated. Proton fluences were from 10 to the 10th to 10 to the 13th p/sq cm. The results show that the diode ideality factor varies between 1.9 and 2.1, indicating that the dominant current component is due to the recombination of electron-hole pairs via deep-level traps in the junction space charge region of these diodes. The recombination current increases with increasing proton fluence and proton energy. The reduction of open circuit voltage, short circuit current, and conversion efficiency in the irradiated cells relates directly to the density of the deep-level defects induced by proton irradiation.

Li, S. S.↗
NASA NTRS1994

Life test of a xenon hollow cathode for a space plasma contractor

A plasma contacting device using a hollow cathode for plasma production has been baselined for use on the Space Station. This application will require reliable, continuous operation of the cathode at electron emission currents of between 0.75 and 10 A for two years (17,500 hours). In order to validate life-time capability, a hollow cathode, operated in a diode configuration, has been tested for more than 8600 hours of stable discharge operation as of March 30, 1994. This cathode is operated at a steady-state emission current of 12.0 and a fixed xenon flow rate of 4.5 sccm. Discharge voltage and cathode temperature have remained relatively stable at approximately 12.9 V and 1260 C during the test. The test has experienced 7 shutdowns to date. In all instances, the cathode was reignited at about 42 V and resumed stable operation. This test represents the longest demonstration of stable operation of high current (greater than 1A) xenon hollow cathodes reported to date.

Sarver-Verhey, Timothy R.↗
NASA NTRS2005

Mid-IR interband cascade lasers

Efficient mid-IR interband cascade (IC) lasers are developed based on 111-V semiconductor materials to cover wavelength range from 2.7 to 5.6 (mu)m. These IC lasers reuse injected electrons in cascade stages for photon generation with high quantum efficiency to achieve high output powers. Also, IC lasers have low threshold current density with very efficient use of applied voltage, resulting in reduced power consumptions. Single-mode distributed feedback lasers have been made, and integrated into aircraft and balloon instrument which made measurements of CH4 and HCI. In this work, the characteristics of IC lasers and their recent development are reviewed.

mid - infrared↗
DOE OSTI2024

Characterization of Mn 5 Ge 3 Contacts on a Shallow Ge/SiGe Heterostructure

Mn 5 Ge 3 is a ferromagnetic phase of the Mn-Ge system that is a potential contact material for efficient spin injection and detection. Here, we investigate the creation of Mn 5 Ge 3 -based contacts on a Ge/SiGe quantum well heterostructure via solid-state synthesis. X-ray diffraction spectra fitting indicates the formation of Mn 5 Ge 3 -based contacts on bulk Ge and Ge/SiGe. High-resolution scanning transmission electron microscopy imaging and energy dispersive X-ray spectroscopy verify the correct Mn 5 Ge 3 -based phase formation. Schottky diode measurements, transmission line measurements, and Hall measurements reveal that Mn 5 Ge 3 -based contacts serve as good p-type contacts for Ge/SiGe quantum well heterostructures due to having a low Schottky barrier height of 0.10 eV (extracted from a Mn 5 Ge 3 /n-Ge analogue) and a contact resistance in the order of 1 kΩ. Furthermore, we show that these electrical characteristics have a gate-voltage dependence, thereby providing tunability.

36 MATERIALS SCIENCE↗
NASA NTRS1989

A heat-driven monochromatic light source

The efficiency with which heat may be converted into resonance radiation in a cesium thermionic diode is investigated theoretically. An analytical model of a thermionic converter is used which combines the coupled effects of line radiation transport, excited-state kinetics, and plasma diffusion. Operating regimes are established for various degrees of optical density in the plasma. The results indicate that monochromatic radiation can be produced with efficiencies on the order of 30 percent, provided that there is an adequate voltage drop across the plasma. A drop of 1 V was used since it can be maintained without any electrical power input to the device. It is found that high efficiencies are ude to the higher interelectrode distances which the solutions accommodate, and that radiation can be generated efficiently, even with optically dense gases.

Stefani, Francis↗
NASA NTRS2010

Miniature Lightweight Ion Pump

This design offers a larger surface area for pumping of active gases and reduces the mass of the pump by eliminating the additional vacuum enclosure. There are three main components to this ion pump: the cathode and anode pumping elements assembly, the vacuum enclosure (made completely of titanium and used as the cathode and maintained at ground potential) containing the assembly, and the external magnet. These components are generally put in a noble diode (or differential) configuration of the ion pump technology. In the present state of the art, there are two cathodes, one made of titanium and the other of tantalum. The anodes are made up of an array of stainless steel cylinders positioned between the two cathodes. All the elements of the pump are in a vacuum enclosure. After the reduction of pressure in this enclosure to a few microns, a voltage is applied between the cathode and the anode elements. Electrons generated by the ionization are accelerated toward the anodes that are confined in the anode space by the axial magnetic field. For the generation of the axial field along the anode elements, the magnet is designed in a C-configuration and is fabricated from rare earth magnetic materials (Nd-B-Fe or Sm-Co) possessing high energy product values, and the yoke is fabricated from the high permeability material (Hiperco-50A composed of Fe-Co-V). The electrons in this region collide with the gas molecules and generate their positive ions. These ions are accelerated into the cathode and eject cathode material (Ti). The neutral atoms deposit on the anode surfaces. Because of the chemical activity of Ti, the atoms combine with chemically active gas molecules (e.g. N2, O2, etc.) and remove them. New layers of Ti are continually deposited, and the pumping of active gases is thus accomplished. Pumping of the inert gases is accomplished by their burial several atomic layers deep into the cathode. However, they tend to re-emit if the entrapping lattice atoms are sputtered away. For stable pumping of inert gases, one side of the cathode is made of Ta. Impaction on Ta produces energetic, neutral atoms that pump the inert gases on the anode structure at the peripheral areas of the cathodes (between anode rings). For inert gases stability, a post design has been implemented. Here, posts of cathode material (Ti) are mounted on the cathode. These protrude into the initial part of the anode elements. Materials sputtered from the posts condense on the anode assembly and on the cathode plane at higher rates than in the normal diodes due to enhanced sputtering at glancing angles from geometrical considerations. This increases pumping by burial. This post design has enhanced pumping rates for both active and inert gases, compared with conventional designs.

Sinha, Mahadeva P.↗
DOE OSTI2020

In-situ Microscopy Characterization of Cu(In,Ga)Se2 Potential-Induced Degradation

We report on the role of sodium in potentialinduced degradation (PID) of Cu(In, Ga)Se 2 (CIGS) solar cells. In-situ microscopy characterizations on AFM platform were performed on two stressed CIGS device under room temperature (RT) and high temperature (HT) at 85 degrees C. During PID stressing we observed depletion region gets wider as Na migrates, p-n junction becomes leaky at RT for over a month; and similar junction evolution was observed for HT-stressed sample, eventually the junction collapsed after 18 hours. The diode behaviors were confirmed by dark I-V measurement. Time-of Flight secondary-ion mass spectrometry reveals that the Na accumulates on ZnO and CdS side, as well as the upper layer of CIGS layer. The results indicate that Na drifted by the voltage applied on the soda-lime glass, then diffuse through the whole device. And the sodium profiles have different points of evolution due to the temperature differences between the two stressed samples. The consistent results unambiguously show how Na from substrate glass causes PID in CIGS solar cells.

14 SOLAR ENERGY↗