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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

NiGa 2 O 4 interfacial layers in NiO/Ga 2 O 3 heterojunction diodes at high temperature

NiO/Ga 2 O 3 heterojunction diodes have attracted attention for high-power applications, but their high temperature performance and reliability remain underexplored. Here, we report the time evolution of the electrical properties in the widely studied p-NiO/n-Ga 2 O 3 heterojunction diodes and formation of NiGa 2 O 4 interfacial layers at high temperatures. Results of our thermal cycling experiment show an initial leakage current increase which stabilizes after sustained thermal load, due to reactions at the NiO–Ga 2 O 3 interface. High-resolution TEM microstructure analysis of the devices after thermal cycling indicates that the NiO–Ga 2 O 3 interface forms a ternary compound at high temperatures, and thermodynamic calculations suggest the formation of the spinel NiGa 2 O 4 layer between NiO and Ga 2 O 3 . First-principles defect calculations find that NiGa 2 O 4 shows low p-type intrinsic doping and hence can serve to limit electric field crowding at the interface. Vertical NiO/ Ga 2 O 3 diodes with intentionally grown 5 nm thin spinel-type NiGa 2 O 4 interfacial layers show an excellent device ON/OFF ratio of >10 10 (± 3 V), V ON of ~1.9 V, and increased breakdown voltage of ~1.2 kV for an initial unoptimized 300 lm diameter device. These p–n heterojunction diodes are promising for high-voltage, high temperature applications.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS2004

Fabrication of a novel gigabit/second free-space optical interconnect - photodetector characterization and testing and system development

The time when computing power is limited by the copper wire inherent in the computer system and not the speed of the microprocessor is rapidly approaching. With constant advances in computer technology, many researchers believe that in only a few years, optical interconnects will begin to replace copper wires in your Central Processing Unit (CPU). On a more macroscopic scale, the telecommunications industry has already made the switch to optical data transmission as, to date, fiber optic technology is the only reasonable method of reliable, long range data transmission. Within the span of a decade, we will see optical technologies move from the macroscopic world of the telecommunications industry to the microscopic world of the computer chip. Already, the communications industry is marketing commercially available optical links to connect two personal computers, thereby eliminating the need for standard and comparatively slow wired and wireless Ethernet transfers and greatly increasing the distance the computers can be separated. As processing demands continue to increase, the realm of optical communications will continue to move closer to the microprocessor and quite possibly onto the microprocessor itself. A day may come when copper connections are used only to supply power, not transfer data. This summer s work marks some of the beginning stages of a 5 to 10 year, long-term research project to create and study a free-space, 1 Gigabit/sec optical interconnect. The research will result in a novel fabricated, chip-to-chip interconnect consisting of a Vertical Cavity Surface Emitting Laser (VCSEL) Diode linked through free space to a Metal- Semiconductor-Metal (MSM) Photodetector with the possible integration of microlenses for signal focusing and Micro-Electromechanical Systems (MEMS) devices for optical signal steering. The advantages, disadvantages, and practicality of incorporating flip-chip mounting technologies will also be addressed. My work began with the design and construction of a test setup for the experiment and then appropriate characterization of the test system. Specifically, I am involved in the characterization of a commercially available 1550nm wavelength, 5mW diode laser and a study of its modulation bandwidth. Commercially produced photodetectors as well as the incorporation of microwave technology, in the form of RF input and output, are used in the characterization procedure. The next stage involves the use of a probe station and network analyzer to characterize and test a series of photodetectors fabricated on a 2 inch, Indium Gallium Arsenide (InGaAs) wafer in the Branch s microlithography lab. Other project responsibilities include, but are not limited to the incorporation of a transimpedance amplifier to the photodetector circuit; a study of VCSEL technology; bit error rate analysis of an optical interconnect system; and analysis of free space divergence of the VCSEL, optical path length of the interconnect; and any other pertinent optical properties of the one gigabit per second interconnect for fabrication and testing.

Savich, Gregory R.↗
DOE OSTI2024

Detecting defects that reduce breakdown voltage using machine learning and optical profilometry

Abstract Semiconductor wafer manufacturing relies on the precise control of various performance metrics to ensure the quality and reliability of integrated circuits. In particular, GaN has properties that are advantageous for high voltage and high frequency power devices; however, defects in the substrate growth and manufacturing are preventing vertical devices from performing optimally. This paper explores the application of machine learning techniques utilizing data obtained from optical profilometry as input variables to predict the probability of a wafer meeting performance metrics, specifically the breakdown voltage (V bk ). By incorporating machine learning techniques, it is possible to reliably predict performance metrics that cause devices to fail at low voltage. For diodes that fail at a higher (but still below theoretical) breakdown voltage, alternative inspection methods or a combination of several experimental techniques may be necessary.

42 ENGINEERING↗
NASA NTRSDate not supplied

Three years of observations from the International Space Station (ISS) by the Stratospheric Aerosol and Gas Experiment III (SAGE III/ISS)

After completion of the robot installation on the International Space Station (ISS) in early March 2017 as an external hosted science payload, the Stratospheric Aerosol and Gas Experiment (SAGE) III became the newest member to the family of space-based solar occultation instruments operated by NASA to investigate the Earth’s upper atmosphere since the late 1970s. One of three identical instruments, the SAGE III/ISS mission was revived in the early 2010s with a primary objective to monitor the vertical distribution of aerosol, ozone and other trace gases to enhance understanding of ozone recovery and climate change processes in the upper atmosphere. Presented here is the mission architecture, its implementation, and data produced by SAGE III/ISS, including their precision and coverage. The 51.6-degree inclined orbit of the ISS is well-suited for solar occultation and provides near-global observations on a monthly basis with coverage of low and mid-latitudes similar to that of the SAGE II mission, which operated over two decades. The nominal science products, derived from sampling spectra covering 290nm to 1030nm and a photo-diode near 1550 nm, include high resolution vertical profiles of ozone, nitrogen dioxide and water vapor, along with multi-wavelength aerosol extinction. Although in the visible portion of the spectrum the brightness of the Sun is a million times that of the full Moon, the SAGE III instrument design covers this large dynamic range, performing lunar occultations on a routine basis to augment the solar products. The standard lunar products include ozone and nitrogen trioxide. Routine observations began June 2017 and continue to the present. This has enabled observations of significant perturbations of the stratosphere induced by three different wildfire events (two of which were record setting), four volcanic eruptions and two changes of the Quasi-Biennial Oscillation (QBO) phase, as represented in the standard data products.

ozone↗
NASA NTRS2011

Method for Measuring Collimator-Pointing Sensitivity to Temperature Changes

For a variety of applications, it is important to measure the sensitivity of the pointing of a beam emerging from a collimator, as a function of temperature changes. A straightforward method for carrying out this measurement is based on using interferometry for monitoring the changes in beam pointing, which presents its own problems. The added temperature dependence and complexity issues relating to using an interferometer are addressed by not using an interferometer in the first place. Instead, the collimator is made part of an arrangement that uses a minimum number of low-cost, off-the-shelf materials and by using a quad diode to measure changes in beam pointing. In order to minimize the influence of the test arrangement on the outcome of the measurement, several steps are taken. The collimator assembly is placed on top of a vertical, 1-m-long, fused silica tube. The quad diode is bonded to a fused silica bar, which, in turn, is bonded to the lower end of the fused silica tube. The lower end of the tube rests on a self-aligning support piece, while the upper end of the tube is kept against two rounded setscrew tips, using a soft rubber string. This ensures that very little stress is applied to the tube as the support structure changes dimensions due to thermal expansion. Light is delivered to the collimator through a bare fiber in order to minimize variable bending torque caused by a randomly relaxing, rigid fiber jacket. In order to separate the effect of temperature on the collimator assembly from the effect temperature has on the rest of the setup, multiple measurements are taken with the collimator assembly rotated from measurement to measurement. Laboratory testing, with 1-m spacing between the collimator and the quad diode, has shown that the sensitivity of the arrangement is better than 100 nm rms, over time spans of at least one hour, if the beam path is protected from atmospheric turbulence by a tube. The equivalent sensitivity to detecting changes in pointing angle is 100 nanoradians.

Abramovici, Alex↗
DOE OSTI2025

Three-dimensional photoluminescence imaging of threading dislocations in GaN by sub-band optical excitation

GaN is rapidly gaining attention for implementation in power electronics but is still impacted by its high density of threading dislocations (TDs), which have been shown to facilitate current leakage through devices limiting their performance and reliability. Here, we discuss a novel implementation of photoluminescence (PL) imaging to study TDs in regions within vertically structured p-i-n GaN (PIN) diodes consisting of metalorganic chemical vapor deposition (MOCVD) epitaxial layers grown on ammonothermal GaN (am-GaN) substrates. PL imaging with a sub-bandgap excitation energy (3.1 eV) reveals TDs with excellent clarity in three dimensions within the am-GaN substrate. Galvanometric-driven PL imaging allows the microstructure of hundreds of devices to be characterized in a single session, enhancing the screening process through the addition of device specific TD location tracking and density mapping. The visibility, structural characteristics, luminescent nature and evolution of TDs through the GaN growth process are described, potentially providing the ability to define TD structures associated with leakage current.

36 MATERIALS SCIENCE↗
NASA NTRS1994

Column measurements of stratospheric trace species over Are, Sweden in the winter of 1991-1992

Total vertical column amounts of stratospheric HCl, HF, ClONO2 and HNO3 are reported from high resolution infrared solar absorption spectra taken during the European Arctic Stratospheric Ozone Experiment (EASOE) in the winter of 1991-1992. These ground based measurements were made near Are in North Sweden (63.4 deg N, 13.1 deg E) at an altitude of 800 m using a Fourier transform spectrometer and tunable diode laser heterodyne spectrometer. On 9th January 1992 the HCl vertical column dropped to 1.2 x 10(exp 15) molecules/sq cm from a November average of 3.6 x 10(exp 15) molecules/sq cm. The HCl drop occurred at a time when Are was below the polar vortex and the lower stratospheric ClO column above Are was elevated to approximately 2 x 10(exp 15) molecules/sq cm as measured by the Microwave Limb Sounder experiment on the Upper Atmosphere Research Satellite. These measurements indicate conversion of lower stratospheric chlorine from reservoir to chemically active forms.

Bell, W.↗
NASA NTRS1980

The laser heterodyne spectrometer - New sensor for the 80's

The paper deals with the basic concepts in optical heterodyne receivers with tunable diode lasers, operating in the thermal infrared. Simulation retrievals of vertical profiles of trace atmospheric gas species are carried out on the basis of heterodyne receiver performance parameters. Operational tests show a high signal-to-noise ratio in measuring gas absorption features. The results demonstrate the potential power of optical heterodyne receivers, and it is concluded that during the eighties they will become the major tool for measuring the earth's atmosphere and other planetary atmospheres.

Katzberg, S. J.↗
DOE OSTI2024

Breakdown characteristics analysis of kV-class vertical GaN PIN rectifiers by wafer-level sub-bandgap photoluminescence mapping

This work reports analysis of the reverse-bias breakdown characteristics of homojunction gallium nitride (GaN) p–i–n (PIN) rectifiers fabricated on bulk GaN substrates. Sub-bandgap photoluminescence mapping at room temperature as a contactless, non-destructive wafer inspection method was performed to analyze the impact of material properties on grown GaN PIN diodes and to study the correlation between defect types and breakdown characteristics of vertical GaN PIN rectifiers. Under the sub-bandgap excitation, yellow luminescence is dominant. The premature breakdown characteristics of the fabricated kV-class vertical GaN PIN rectifiers with nitrogen-implanted floating guard rings are found to be associated with material defects and deep level complexes. Photoluminescence mapping has demonstrated its effectiveness in quantitative analysis of dislocations and other types of defects.

42 ENGINEERING↗
NASA NTRS1984

Integrating IR detector imaging systems

An integrating IR detector array for imaging is provided in a hybrid circuit with InSb mesa diodes in a linear array, a single J-FET preamplifier for readout, and a silicon integrated circuit multiplexer. Thin film conductors in a fan out pattern deposited on an Al2O3 substrate connect the diodes to the multiplexer, and thick film conductors also connect the reset switch and preamplifier to the multiplexer. Two phase clock pulses are applied with a logic return signal to the multiplexer through triax comprised of three thin film conductors deposited between layers. A lens focuses a scanned image onto the diode array for horizontal read out while a scanning mirror provides vertical scan.

Bailey, G. C.↗
NASA NTRS2004

Tropospheric Methane Over the Pacific Basin During TRACE-P

We received funding for the acquisition, statistical analysis, interpretation, and publication of atmospheric methane data collected during the Transport and Chemical Evolution over the Pacific (TRACE-P) mission, flown February through April of 2001. These high precision measurements were made aboard the NASA DC-8 and P-3B aircraft using a fast response, tunable diode laser system, the DACOM instrument. Our analysis focused on the vertical and geographical distribution of this key trace gas, particularly in the context of other data available from the region such as those from the Pacific NOAA CMDL surface sites, and earlier NASA aircraft missions (such as PEM-West A and B). The paper reporting these results, "Large-Scale Distribution of CH4 in the Western Pacific: Sources and Transport from the Asian Continent" by authors K.B. Bartlett, G.W. Sachse, T. Slate, C. Harward, and D.R. Blake, is attached. The dataset of roughly 13,800 CH4 measurements ranged between 1602 ppb in stratospherically impacted air and 2149 ppb in highly polluted air. Overall, we found that CH4 concentrations were highly correlated with trace gases characteristic of a mix of anthropogenic industrial and combustion sources. They were strikingly correlated with ethane (C2H6) in particular, whose major sources are natural gas leakage and biomass burning. Correlation between the two hydrocarbons indicated that these sources may dominate for CH4 as well at this time.

Bartlett, Karen B.↗
NASA NTRS2021

A Nanoscale Vacuum Field Emission Gated Diode with an Umbrella Cathode

A nanoscale field emission vacuum channel gated diode structure is proposed and a tungsten cathode with an umbrella-like geometry and sharp vertical edge is fabricated. The edge of the suspended cathode becomes the field emission surface. Unlike in the traditional transistor with the gate typically located between the source and the drain, the bottom silicon plate becomes the gate here and the anode terminal is located between the umbrella cathode and the gate. The fabricated devices show excellent diode characteristics and the gated diode structure is attractive for extremely low gate leakage.

Vacuum field emission diode↗
NASA NTRS1974

An experiment in manipulator control with proximity sensors

Optical proximity sensors were used in a feedback loop to automatically position a manipulator hand for grasping. The experiment was a simplified one, involving two dimensional motion only. Two proximity sensors were mounted on the hand, and control signals derived from their outputs were used to drive the hand vertically and horizontally. The sensors employ a pulsed gallium arsenide light-emitting diode together with a silicon detector. They indicate, without contact, the approximate distance between the manipulator hand and object in the range from 5 to 12 cm. Positioning within approximately + or - 5 mm was observed. Extension of the technique to general three-dimensional control is briefly discussed.

Johnston, A. R.↗
NASA NTRS1999

The Laser Vegetation Imaging Sensor (LVIS): A Medium-Altitude, Digitization-Only, Airborne Laser Altimeter for Mapping Vegetation and Topography

The Laser Vegetation Imaging Sensor (LVIS) is an airborne, scanning laser altimeter designed and developed at NASA's Goddard Space Flight Center. LVIS operates at altitudes up to 10 km above ground, and is capable of producing a data swath up to 1000 m wide nominally with 25 m wide footprints. The entire time history of the outgoing and return pulses is digitized, allowing unambiguous determination of range and return pulse structure. Combined with aircraft position and attitude knowledge, this instrument produces topographic maps with decimeter accuracy and vertical height and structure measurements of vegetation. The laser transmitter is a diode-pumped Nd:YAG oscillator producing 1064 nm, 10 nsec, 5 mJ pulses at repetition rates up to 500 Hz. LVIS has recently demonstrated its ability to determine topography (including sub-canopy) and vegetation height and structure on flight missions to various forested regions in the U.S. and Central America. The LVIS system is the airborne simulator for the Vegetation Canopy Lidar (VCL) mission (a NASA Earth remote sensing satellite due for launch in 2000), providing simulated data sets and a platform for instrument proof-of-concept studies. The topography maps and return waveforms produced by LVIS provide Earth scientists with a unique data set allowing studies of topography, hydrology, and vegetation with unmatched accuracy and coverage.

Blair, J. Bryan↗
NASA NTRS1981

Vibration characteristics of a laser heterodyne spectrometer tunable diode laser system using a mechanical cooler platform

The Langley Research Center redesigned the cooler test bed hardware for the refrigerator for the purpose of isolating the tunable diode laser (TDL) from the cold tip in a laser heterodyne spectrometer system. Deflection in the lateral and vertical directions were managed on the cold tip and on the TDL. Measurements were analyzed over the frequency range of 0.100 Hz. The results show that the TDL responds approximately one order of magnitude less than that of the cold tip. The redesign of the system provided for adequately isolating the TDL for future operation.

Catherines, J. J.↗
NASA NTRS1991

Aircraft laser infrared absorption spectrometer (ALIAS) for polar ozone studies

The ALIAS instrument is a very high resolution (0.0003/cm) scanning, tunable diode laser spectrometer designed to make direct, simultaneous measurements of NO2, HNO3, HCl, CH4, and either O3 or N2O (including vertical profiles of CH4 and N2O) in the polar stratosphere at sub-part-per-billion level sensitivities over integration times from 3 to 30 s. Unique features include a sample inlet/throttle system designed to achieve near-isokinetic sampling, in PSC events, an in-flight wavelength reference cell rack, mechanical fringe-spoilers, a four-laser/four-detector dewar with 24-hr hold-time operating at a fixed temperature without electrical regulation, and in-flight fast correlation routines for spectral drift compensation prior to spectral addition. Instrument design and test flight results are discussed in the light of ALIAS's role in the Winter 1991 Arctic aircraft stratospheric ozone campaigns out of Fairbanks, Alaska, and Bangor, Maine.

Webster, C. R.↗