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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Non-Micropipe Dislocations in 4H-SiC Devices: Electrical Properties and Device Technology Implications

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vectors greater than or equal to 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = 1c with no hollow core) in densities on the order of thousands per sq cm, nearly 100-fold micropipe densities. While not nearly as detrimental to SiC device performance as micropipes, it has recently been demonstrated that elementary screw dislocations somewhat degrade the reverse leakage and breakdown properties of 4H-SiC p(+)n diodes. Diodes containing elementary screw dislocations exhibited a 5% to 35% reduction in breakdown voltage, higher pre-breakdown reverse leakage current, softer reverse breakdown I-V knee, and microplasmic breakdown current filaments that were non-catastrophic as measured under high series resistance biasing. This paper details continuing experimental and theoretical investigations into the electrical properties of 4H-SiC elementary screw dislocations. The nonuniform breakdown behavior of 4H-SiC p'n junctions containing elementary screw dislocations exhibits interesting physical parallels with nonuniform breakdown phenomena previously observed in other semiconductor materials. Based upon experimentally observed dislocation-assisted breakdown, a re-assessment of well-known physical models relating power device reliability to junction breakdown has been undertaken for 4H-SiC. The potential impact of these elementary screw dislocation defects on the performance and reliability of various 4H-SiC device technologies being developed for high-power applications will be discussed.

Neudeck, Philip G.↗
NASA NTRS2018

Drag De-Orbit Device (D3): A Retractable Device for CubeSat Attitude and Orbit Control using Aerodynamic Forces

The increasing number of CubeSats being launched has raised concerns about orbital debris since most of these satellites have no means of active orbit control. Some technologies exist to increase the surface area of a CubeSat and expedite de-orbit due to aerodynamic drag in low Earth orbit, but most of these devices cannot be retracted and hence cannot be used for orbital maneuvering. This paper discusses the De-Orbit Drag Device (D3) module that is capable of de-orbiting a 12U, 15kg CubeSat from a 700 km circular orbit in under 25 years and can be deployed and retracted to modulate the aerodynamic drag force experienced by the satellite. This facilitates orbital maneuvering using aerodynamic drag and the active targeting of a de-orbit location. In addition, the geometry of this drag device provides 3-axis attitude stabilization of the host CubeSat using aerodynamic and gravity gradient torques which is useful for many missions and provides a predictable aerodynamic profile for use in orbital maneuvering algorithms.

algorithm↗
DOE OSTI2019

Thermoelectric power generation: from new materials to devices

Thermoelectric technology offers the opportunity of direct conversion between heat and electricity, and new and exciting materials that can enable this technology to deliver higher efficiencies have been developed in recent years. This mini-review covers the most promising advances in thermoelectric materials as they pertain to their potential in being implemented in devices and modules with an emphasis on thermoelectric power generation. Classified into three groups in terms of their operating temperature, the thermoelectric materials that are most likely to be used in future devices are briefly discussed. Here, we summarize the state-of-the-art thermoelectric modules/devices, among which nanostructured PbTe modules are particularly highlighted. At the end, key issues and the possible strategies that can help thermoelectric power generation technology move forward are considered.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

Competition between magnetic order and charge localization in Na 2 IrO 3 thin crystal devices thin crystal devices

Spin orbit assisted Mott insulators such as sodium iridate (Na 2 IrO 3 ) have been an important subject of study in recent years. In these materials, the interplay of electronic correlations, spin-orbit coupling, crystal field effects, and a honeycomb arrangement of ions bring exciting ground states, predicted in the frame of the Kitaev model. The insulating character of Na 2 IrO 3 has hampered its integration to an electronic device, desirable for applications, such as the manipulation of quasiparticles interesting for topological quantum computing. Here we show through electronic transport measurements supported by angle-resolved photoemission spectroscopy (ARPES) experiments, that electronic transport in Na 2 IrO 3 is ruled by variable range hopping and it is strongly dependent on the magnetic ordering transition known for bulk Na 2 IrO 3 , as well as on external electric fields. Furthermore, electronic transport measurements allow us to deduce a value for the localization length and the density of states in our Na 2 IrO 3 thin crystal devices, and offer an alternative approach to study insulating 2D-materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2016

Optical Evaluation of Digital Micromirror Devices (DMDs) with UV-Grade Fused Silica, Sapphire, and Magnesium Fluoride Windows and Longterm Reflectance of Bare Devices

Digital micromirror devices (DMDs) are commercial micro-electromechanical systems, consisting of millions of mirrors which can be individually addressed and tilted into one of two states (+/-12deg). These devices were developed to create binary patterns in video projectors, in the visible range. Commercially available DMDs are hermetically sealed and extremely reliable. Recently, DMDs have been identified as an alternative to microshutter arrays for space-based multi-object spectrometers (MOS). Specifically, the MOS at the heart of the proposed Galactic Evolution Spectroscopic Explorer (GESE) uses the DMD as a reprogrammable slit mask. Unfortunately, the protective borosilicate windows limit the use of DMDs in the UV and IR regimes, where the glass has insufficient throughput. In this work, we present our efforts to replace standard DMD windows with custom windows made from UV-grade fused silica, low-absorption optical sapphire (LAOS) and magnesium fluoride (MgF2). We present transmission measurements of the antireflection coated windows and the reflectance of bare (window removed) DMDs. Furthermore, we investigated the long-term stability of the DMD reflectance and experiments for coating DMD active area with a layer of pure aluminum (Al) to boost reflectance performance in the UV spectral range (200−400 nm).

reflectance↗
DOE OSTI2018

Thick Layered Semiconductor Devices with Water Top-Gates: High On–Off Ratio Field-Effect Transistors and Aqueous Sensors

Layered semiconductors show promise as channel materials for field-effect transistors (FETs). Usually, such devices incorporate solid back or top gate dielectrics. Here, we explore deionized (DI) water as a solution top-gate for field-effect switching of layered semiconductors including SnS 2 , MoS 2 , and black phosphorus. The DI water gate is easily fabricated, can sustain rapid bias changes, and its efficient coupling to layered materials provides high on–off current ratios, near-ideal subthreshold swing, and enhanced short-channel behavior even for FETs with thick, bulk-like channels, where such control is difficult to realize with conventional back gating. Screening by the high-k solution gate eliminates hysteresis due to surface and interface trap states and substantially enhances the field-effect mobility. The onset of water electrolysis sets the ultimate limit to DI water gating at large negative gate bias. Measurements in this regime show promise for aqueous sensing, demonstrated here by the amperometric detection of glucose in aqueous solution. In conclusion, DI water gating of layered semiconductors can be harnessed in research on novel materials and devices, and it may with further development find broad applications in microelectronics and sensing.

36 MATERIALS SCIENCE↗
DOE OSTI2024

π-Extended Porphyrin–Phthalocyanine Heterojunction Devices Exhibiting High Ammonia Sensitivity with a Remarkable Light Effect

π-Extended porphyrins represent an attractive class of organic compounds because of their unique photophysical, optoelectronic, and physicochemical properties. Herein, cross-conjugated (Ace-PQ-Ni) and linear-conjugated (AM6) porphyrins are used to build double-layer heterojunction devices by combining them with a lutetium bisphthalocyanine complex (LuPc 2 ). The heterojunction effect at the porphyrin–phthalocyanine interface plays a key role in the charge transport properties. Both devices exhibit exceptionally high ammonia sensitivity at room temperature and under ambient relative humidity, with limit of detection values of 156 and 115 ppb for Ace-PQ-Ni/LuPc 2 and AM6/LuPc 2 sensors, respectively. Interestingly, the Ace-PQ-Ni/LuPc 2 and AM6/LuPc 2 sensors display opposite effects upon light illumination. While the former sensors show largely decreased ammonia sensitivity under light illumination, the current variation of the latter under ammonia is remarkably enhanced with a multiplication factor of 13 and a limit of detection (LOD) of 83 ppb. Here, the striking difference in their sensing properties upon light illumination is attributed to their different π-conjugation pathways (cross-conjugation versus linear conjugation).

conductometric transducer↗
DOE OSTI2021

CdSexTe1-x/CdTe Devices with Reduced Interface Recombination Through Novel Back Contacts and Group-V Doping

Since excellent carrier lifetimes and front interface electronic quality are now achieved, rear interface recombination can limit V OC in CdSexTe1-x/CdTe solar cells. Several back-contact structures for devices were fabricated using combinations of tellurium, aluminum oxide, amorphous silicon, and indium tin oxide (ITO). Time-resolved photoluminescence was used to characterize such structures. We show increasingly improved interface passivation through the subsequent use of aluminum oxide, amorphous silicon, and ITO. Additionally, we show that arsenic-doped absorbers form a more passive interface with numerous back contact structures.

aluminum oxide↗
DOE OSTI2023

A Novel Spatial-Temporal Variational Quantum Circuit to Enable Deep Learning on NISQ Devices

Quantum computing presents a promising approach for machine learning with its capability for extremely parallel computation in high-dimension through superposition and entanglement. Despite its potential, existing quantum learning algorithms, such as Variational Quantum Circuits (VQCs), face challenges in handling more complex datasets, particularly those that are not linearly separable. What’s more, it encounters the deployability issue, making the learning models suffer a drastic accuracy drop after deploying them to the actual quantum devices. To overcome these limitations, this paper proposes a novel spatial-temporal design, namely “ST-VQC”, to integrate nonlinearity in quantum learning and improve the robustness of the learning model to noise. Specifically, ST-VQC can extract spatial features via a novel block-based encoding quantum sub-circuit coupled with a layer-wise computation quantum sub-circuit to enable temporal-wise deep learning. Additionally, a SWAP-Free physical circuit design is devised to improve robustness. These designs bring a number of hyperparameters. After a systematic analysis of the design space for each design component, an automated optimization framework is proposed to generate the ST-VQC quantum circuit. The proposed ST-VQC has been evaluated on two IBM quantum processors, ibm-cairo with 27 qubits and ibmq-lima with 7 qubits to assess its effectiveness. The results of the evaluation on the standard dataset for binary classification show that ST-VQC can achieve over 30% accuracy improvement compared with existing VQCs on actual quantum computers. Moreover, on a non-linear synthetic dataset, the STVQC outperforms a linear classifier by 27.9%, while the linear classifier using classical computing outperforms the existing VQC by 15.58%.

Li, Jinyang↗
DOE OSTI2018

Investigation of interfacial impurities in m-plane GaN regrown p-n junctions for high-power vertical electronic devices

GaN is an attractive material for high-power electronics due to its wide bandgap and large breakdown field. Verticalgeometry devices are of interest due to their high blocking voltage and small form factor. One challenge for realizing complex vertical devices is the regrowth of low-leakage-current p-n junctions within selectively defined regions of the wafer. Presently, regrown p-n junctions exhibit higher leakage current than continuously grown p-n junctions, possibly due to impurity incorporation at the regrowth interfaces, which consist of c-plane and non-basal planes. Here, we study the interfacial impurity incorporation induced by various growth interruptions and regrowth conditions on m-plane p-n junctions on free-standing GaN substrates. The following interruption types were investigated: (1) sample in the main MOCVD chamber for 10 min, (2) sample in the MOCVD load lock for 10 min, (3) sample outside the MOCVD for 10 min, and (4) sample outside the MOCVD for one week. Regrowth after the interruptions was performed on two different samples under n-GaN and p-GaN growth conditions, respectively. Secondary ion mass spectrometry (SIMS) analysis indicated interfacial silicon spikes with concentrations ranging from 5e16 cm -3 to 2e18 cm -3 for the n-GaN growth conditions and 2e16 cm -3 to 5e18 cm-3 for the p-GaN growth conditions. Oxygen spikes with concentrations ~1e17 cm -3 were observed at the regrowth interfaces. Carbon impurity levels did not spike at the regrowth interfaces under either set of growth conditions. We have correlated the effects of these interfacial impurities with the reverse leakage current and breakdown voltage of regrown m-plane p-n junctions.

42 ENGINEERING↗
DOE OSTI2018

A Modular and Flexible High-Frequency-Link Transformer with a Reduced Device Count and Zero High-Side Devices

In general, large power transformers (LPTs) are not interchangeable with each other and their high costs prohibit extensive spare inventories more so considering that on an average only 1.3 LPTs are manufactured for individual design. The latter pose a further challenge since given that the several existing LPTs are reaching their end of service lives, loss of plurality of such LPTs, that form the backbone of U.S. power grid, will clearly run into the problem of energy security related to the non-availability of sufficient spares (and extended lead time) exacerbated further by the fact that these spares are not interchangeable for installations at different locations. Conventional LPT cost millions of dollars and weighs significantly between approximately 100 and 400 tons. Two raw materials—copper and electrical steel—account for over 50 percent of the total cost of an LPT. In recent years, the price volatility of these two commodities in the global market has affected the manufacturing conditions and procurement strategy for LPTs. Transportation is also an important element of the total LPT cost, because an LPT can weigh significantly and often requires long-distance transport. Transporting an LPT is challenging—its large dimensions and heavy weight pose unique requirements to ensure safe and efficient transportation. Current road, rail, and port conditions are such that transportation is taking more time and becoming more expensive. Conventional low-frequency LPTs typically follow a monolithic approach to design due to historical reasons that need to transition to more modular and flexible (e.g., in voltage, impedance, and power flow) designs with ability to seamlessly/near-seamlessly scale. They should also have the ability to incorporate new technologies without in all cases redoing a LPT design from scratch. Given that the cost of raw materials has continued to increase, next-generation LPTs need to pursue avenues for reducing these costs. An added necessity is to reduce the transportability cost, which is significant in conventional LPTs. Further, given that LPTs are for the long term, they need to be durable, efficient, and fault tolerant with overloading capability. Given this backdrop, the objective and accomplishment of this one-year DOE (SPONSOR) R&D project, led by small business NextWatt LLC (PRIME, Lead PI: Dr. Sudip K. Mazumder) and University of Arkansas at Fayetteville (SUBAWARDEE, PI: Dr. Juan Balda) were to explore the design of a (8 – 20 kHz) high-frequency-link (HFL) based 100-MVA LPT with nominal voltage of 115/69 kV, with $15 - $22 dollars US per kVA when manufactured in “moderate” volume, with 99% energy-conversion efficiency, with 300% reduction in both volume and weight compared to a conventional LPT with the same electrical ratings, with impedance variation greater than 5%, with direct AC/AC power conversion capability, with very-high energy-conversion efficiency (using wide-bandgap SiC based field effect MOSFET devices) over a wide operating temperature, with reduction in both volume and weight with regard to conventional low frequency LPT, and with significant reduction in number of devices compared to state of the art solid state transformer topology.

24 POWER TRANSMISSION AND DISTRIBUTION↗