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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
NASA NTRS1982

Mathematical analysis of the Photovoltage Decay (PVD) method for minority carrier lifetime measurements

When the diffusion length of minority carriers becomes comparable with or larger than the thickness of a p-n junction solar cell, the characteristic decay of the photon-generated voltage results from a mixture of contributions with different time constants. The minority carrier recombination lifetime tau and the time constant l(2)/D, where l is essentially the thickness of the cell and D the minority carrier diffusion length, determine the signal as a function of time. It is shown that for ordinary solar cells (n(+)-p junctions), particularly when the diffusion length L of the minority carriers is larger than the cell thickness l, the excess carrier density decays according to exp (-t/tau-pi(2)Dt/4l(2)), tau being the lifetime. Therefore, tau can be readily determined by the photovoltage decay method once D and L are known.

Vonroos, O. H.↗
NASA NTRS1992

Minor satellites and the Gaspra encounter

Observational evidence, especially from occultations and radar, indicate that satellites of minor planets are numerous and commonplace. This leads to the prediction that the Galileo spacecraft will find many such 'minor satellites' at the upcoming close encounter with minor planet 951 Gaspra. If such objects are found, this argues strongly against the current theory of minor planet origin from the primeval solar nebula.

Vanflandern, Thomas C.↗
NASA NTRS1995

Research project for increasing pool of minority engineers

The Tennessee State University (TSU) Research Project for Increasing the Pool of Minority Engineers is designed to develop engineers who have academic and research experiences in technical areas of interest to NASA. These engineers will also have some degree of familiarity with NASA Lewis Research Center as a result of interaction with Lewis engineers, field trips and internships at Lewis. The Research Project has four components, which are: (1) Minority Introduction to Engineering (MITE), a high school precollege program, (2) engineering and technology previews, (3) the NASA LeRC Scholars program which includes scholarships and summer internships, and (4) undergraduate research experiences on NASA sponsored research. MITE is a two-week summer engineering camp designed to introduce minority high school students to engineering by exposing them to: (1) engineering role models (engineering students and NASA engineer), (2) field trips to engineering firms, (3) in addition to introducing youth to the language of the engineer (i.e., science, mathematics, technical writing, computers, and the engineering laboratory). Three MITE camps are held on the campus of TSU with an average of 40 participants. MITE has grown from 25 participants at its inception in 1990 to 118 participants in 1994 with participants from 17 states, including the District of Columbia, and 51 percent of the participants were female. Over the four-year period, 77 percent of the seniors who participated in MITE have gone to college, while 53 percent of those seniors in college are majoring in science, engineering or mathematics (SEM). This first Engineering and Technology Previews held in 1993 brought 23 youths from Cleveland, Ohio to TSU for a two-day preview of engineering and college life. Two previews are scheduled for 1994-1995. The NASA LeRC Scholars program provides scholarships and summer internships for minority engineering students majoring in electrical or mechanical engineering. Presently six (6) engineering students are in the Scholars program. The average GPA for the scholars is 3.239. Each scholar must maintain a minimum GPA of 3.000/4.000. NASA LeRC Fred Higgs has been awarded a GEM Fellowship. In addition, he will be presenting a paper entitled 'Design of Helical Spring Using Probabilistic Design Methodology' at the Middle Tennessee Section ASME Student Design Presentations in Nashville on March 23rd and at the National Conference on Undergraduate Research to be held at Union College, Schenectady, New York on April 20-22, 1995. Each of the scholars is working on one of the three NASA sponsored research projects in the college.

Rogers, Decatur B.↗
NASA NTRS1998

Perimeter Governed Minority Carrier Lifetimes in 4H-SiC p+n Diodes Measured by Reverse Recovery Switching Transient Analysis

Minority carrier lifetimes in epitaxial 4H-SiC p-n junction diodes were measured via an analysis of reverse recovery switching characteristics. Behavior of reverse recovery storage time (t(sub s)) as a function of initial ON-state forward current (I(sub f)) and OFF-state reverse current (I(sub R)) followed well-documented trends which have been observed for decades in silicon p-n rectifiers. Average minority carrier (hole) lifetimes (tau(sub p)) calculated from plots of t(sub s) vs I(sub R)/I(sub F) strongly decreased with decreasing device area. Bulk and perimeter components of average hole lifetimes were separated by plotting tau(sub p) as a function of device perimeter-to-area ratio (P/A). This plot reveals that perimeter recombination is dominant in these devices, whose areas are all less than 1 square mm. The bulk minority carrier (hole) lifetime extracted from the 1/Tau(sub p) vs P/A plot is approximately 0.7 microns, well above the 60 ns to 300 ns average lifetimes obtained when perimeter recombination effects are ignored in the analysis. Given the fact that there has been little previous investigation of bipolar diode and transistor performance as a function of perimeter-to-area ratio, this work raises the possibility that perimeter recombination may be partly responsible for poor effective minority carrier lifetimes and limited performance obtained in many previous SiC bipolar junction devices.

Neudeck, Philip G.↗
NASA NTRS1998

Perimeter Governed Minority Carrier Lifetimes in 4H-SiC p(+)-n Diodes Measured by Reverse Recovery Switching Transient Analysis

Minority carrier lifetimes in epitaxial 4H-SiC p(+)-n junction diodes were measured via an analysis of reverse recovery switching characteristics. Behavior of reverse recovery storage time (t(s)) as a function of initial ON-state forward current (I(F)) and OFF-state reverse current (I(R)) followed well-documented trends which have been observed for decades in silicon p-n rectifiers. Average minority carrier (hole) lifetimes (tau(p)) calculated from plots of t(s) vs I(R)/I(F) strongly decreased with decreasing device area. Bulk and perimeter components of average hole lifetimes were separated by plotting 1/tau(p) as a function of device perimeter-to- area ratio (P/A). This plot reveals that perimeter recombination is dominant in these devices, whose areas are all less than 1 sq mm. The bulk minority carrier (hole) lifetime extracted from the 1/tau(p) vs P/A plot is approximately 0.7 micro-s, well above the 60 ns to 300 ns average iit'eptimes obtained when perimeter recombination effects are ignored in the analysis. Given the fact that there has been little previous investigation of bipolar diode and transistor performance as a function of perimeter-to-area ratio, this work raises the possibility that perimeter recombination may be partly responsible for poor effective minority carrier lifetimes and limited performance obtained in many previous SiC bipolar junction devices.

Neudeck, Philip G.↗
NASA NTRS2003

Research Project for Increasing the Pool of Minority Engineers

The NASA Glenn Research Center (GRC) funded the 2001-2002 Tennessee State University (TSU) Research Project for increasing the pool of minority engineers. The NASA GRC/TSU Research Project is designed to develop a cadre of SMET professionals who have academic and research expertise in technical areas of interest to NASA, in addition to having some familiarity with the mission of the NASA Glenn Research Center. The goal of increasing minority participation in SMET disciplines was accomplished by: (1) introducing and exposing 96 minority youth to Science, Math, Engineering, and Technology (SMET) careers and to the required high school preparation necessary to make high school graduation, college attendance and engineering careers a reality through the campus based pre-college SMET program: Minority Introduction to Engineering (MITE); (2) by providing financial support through scholarships for four (4) TSU engineering students to NASA; (3) familiarization with the SMET profession and with NASA through summer internships at NASA GRC for two TSU NASA Glenn Research Scholars; and experiences through research internships at NASA GRC.

Gott, Susan F.↗
NASA NTRS2007

Minor Elements in Nakhlite Pyroxenes: Does Cr Record Changes in REDOX Conditions during Crystallization?

Nakhlites are olivine-bearing clinopyroxene cumulates. Based on petrographic characteristics, they may be divided into groups that cooled at different rates and may have been formed at different depths in a single flow. The order of cooling rate from slowest to fastest is NWA998<Lafayette < Governador Valadares approx. Nakhla < Yamato000593 < NWA817 approx. MIL03346. Nakhlite cumulus pyroxene grains consist of large cores that are nearly homogeneous in major element composition surrounded by thin rims that are zoned to Fe-rich compositions. Detailed study of these pyroxenes is important because they retain a record of the crystallization history of the nakhlite magma. Moreover, because the composition of the nakhlite parent melt cannot be directly determined, inversion of the major and minor element composition of the cumulate pyroxene cores can be used to estimate the composition of that melt. Moreover, minor and trace element zoning of pyroxenes can provide information about the oxidation conditions under which these samples crystallized. Thus it is important to understand the major and minor element zoning in the cumulus pyroxenes. While major elements are nearly homogeneous, minor elements exhibit distinctive zoning patterns that vary from one nakhlite to another. This abstract reports unusual Cr zoning patterns in pyroxenes from MIL03346 (MIL) and contrast these with pyroxenes from Y593 and Nakhla.

McKay, G.↗
DOE OSTI2025

What Is the Limit of Quantification for the Minor Phase in Time-of-Flight Neutron Diffraction? A Case Study on Fe and Ni Powder Mixtures at VULCAN

A phase present in small quantities within materials may not simply serve as a secondary component; it can play a crucial role in determining the integrity, properties, and performance of the material. These minor but important phases usually draw attention in material design and processing for fundamental understanding as well as material quality control. Accurately quantifying a minor phase amid a majority phase, especially at extremely low fractions, remains a challenging task. Time-of-flight neutron diffraction, coupled with advanced pattern analysis techniques like Rietveld refinement, is a powerful tool for crystal structure identification and phase quantification. The deep penetrating capability of neutrons enables the detection and quantification of trace phases within materials. In this study, the quantification limits of time-of-flight neutron diffraction were explored using the VULCAN diffractometer at the Spallation Neutron Source, using Fe–Ni powder mixtures as a sample system. By comparing the refinement results to the known weighed values, it was determined that the reliable quantification of a minor Ni phase is achievable down to about 0.1 wt% while a Ni fraction as low as 0.02 wt% is difficult to trace. Effective control of the refinement parameters, especially the profile function parameters, are found to significantly influence the convergence of fittings and the accuracy of phase quantification.

Rietveld refinement↗
DOE OSTI2023

Radiation Damage and Mitigation by Minority Carrier Injection in InAsSb/AlAsSb Heterojunction Barrier Mid-Wave Infrared Detector

Here, the effects of gamma and proton irradiation, and of forward bias minority carrier injection, on photo-response were investigated for InAsSb/AlAsSb pBn mid-wave infrared (MWIR) detectors with an engineered majority-carrier barrier. Room-temperature gamma irradiation had an insignificant effect on 77 K photo-response. Gamma irradiation at 77 K detector temperature, however, decreased in situ photo-response by 19% after a cumulative dose of ~ 500 krad(Si). Subsequent forward bias minority carrier injection had no effect on photo-response. The 77 K detectors irradiated with 30 MeV protons up to 2 Mrad(Si) had photo-response degraded by up to 70%, but here forward bias minority carrier (hole) injection caused up to 12% recovery that persisted more than 30 min. These results suggest a mitigation strategy for maintaining the photo-response of similar detectors in radiation environments that cause displacement damage defects.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Minority carrier lifetime and photoluminescence of mid-wave infrared InAsSbBi

Time-resolved photoluminescence measurements are reported for InAsSbBi alloys grown by molecular beam epitaxy with Bi mole fractions ranging from 0 to 0.8%, yielding minority carrier lifetimes on the order of hundreds of nanoseconds. The minority carrier lifetimes extracted from the time-resolved photoluminescence measurements are comparable to those of lattice-matched InAsSb grown at the same respective temperatures. Nomarski imaging shows that smooth, droplet-free surface morphologies are obtained in 1 μm thick InAsSbBi epilayers grown at temperatures between 360 and 380 °C. The alloy composition-dependent bandgap energies for the InAsSbBi samples are determined from temperature-dependent steady-state photoluminescence measurements and compared with the tetragonal distortion measured by x-ray diffraction to determine the Sb and Bi mole fractions of each sample. The minority carrier lifetime and the achievable extension of the InAsSb(Bi) cut-off wavelength are analyzed as functions of alloy composition and compared with the performance of InAsSb layers with similar growth parameters.

Petluru, Priyanka (ORCID:0000000257154284)↗
DOE OSTI2023

Utility of Shockley–Read–Hall analysis to extract defect properties from semiconductor minority carrier lifetime data

The semiconductor minority carrier lifetime contains information about several important material properties, including Shockley–Read–Hall defect levels/concentrations and radiative/Auger recombination rates, and the complex relationships between these parameters produce a non-trivial temperature-dependence of the measured lifetime. It is tempting to fit temperature-dependent lifetime data to extract the properties of the Shockley–Read–Hall recombination centers; however, without a priori knowledge of the distribution of the Shockley–Read–Hall states across the bandgap, this fit problem is under-constrained in most circumstances. Shockley–Read–Hall lifetime data are not well-suited for the extraction of Shockley–Read–Hall defect levels but can be used effectively to extract minority carrier recombination lifetimes. The minority carrier recombination lifetime is observed at temperatures below 100 K in a Si-doped n-type InGaAs/InAsSb superlattice, and deviation from its expected temperature-dependence indicates that the capture cross section of the defect associated with Si-doping has an activation energy of 1.5 meV or a characteristic temperature of 17 K. This lower temperature regime is also preferrable for the analysis of the physics of defect introduction with displacement-damage-generating particle irradiation.

Physics↗
DOE OSTI2023

A declining major merger fraction with redshift in the local Universe from the largest-yet catalogue of major and minor mergers in SDSS

It is difficult to accurately identify galaxy mergers and it is an even larger challenge to classify them by their mass ratio or merger stage. In previous work we used a suite of simulated mergers to create a classification technique that uses linear discriminant analysis to identify major and minor mergers. Here, we apply this technique to 1.3 million galaxies from the SDSS DR16 photometric catalogue and present the probability that each galaxy is a major or minor merger, splitting the classifications by merger stages (early, late, post-coalescence). We present publicly available imaging predictor values and all of the above classifications for one of the largest-yet samples of galaxies. We measure the major and minor merger fraction (f merg ) and build a mass-complete sample of galaxies, which we bin as a function of stellar mass and redshift. For the major mergers, we find a positive slope of fmerg with stellar mass and negative slope of f merg with redshift between stellar masses of 10.5 < M * (log M ⊙ ) < 11.6 and redshifts of 0.03 < z < 0.19. We are able to reproduce an artificial positive slope of the major merger fraction with redshift when we do not bin for mass or craft a complete sample, demonstrating the importance of mass completeness and mass binning. Further, we determine that the positive trend of the major merger fraction with stellar mass is consistent with a hierarchical assembly scenario. The negative trend with redshift requires that an additional assembly mechanism, such as baryonic feedback, dominates in the local Universe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

A New Method for the Evaluation of Majority and Minority Carrier Contact Resistivity of Polysilicon on Oxide Contacts

In this contribution we present a novel technique for characterizing the majority and minority carrier contact resistivity in polysilicon on oxide passivating contacts. Traditionally, contact resistivity is measured through the Transfer Length Method (TLM). This method presents difficulties when measuring the minority carrier contact due to the presence of a blocking diode which prevents current flow between the pads. Our novel method is performed by creating a unipolar device which has the same contact on both sides (either symmetric n-type or symmetric p-type) and metalizing the device with a grid on one side, and a full metal contact on the back (the same pattern that will be used in a final cell). We then measure the resistance across the device at increasing illumination. Since the resistivity of the wafer is a function of carrier density, when increasing illumination, the wafer resistivity decreases. We can then fit modeling equations to the measured resistivity and extrapolate the fit to infinite illumination where only the contact resistivity is measured to accurately measure both the minority and majority carrier contact resistivity.

current measurement↗
DOE OSTI2025

ATONA TE-TIMS of minor uranium isotopes (FY25 Mid-Year Report)

Isotopic measurements of the minor isotopes of uranium ( 233 U, 234 U, 236 U) are indispensable measures for material accountability and processing history but can be particularly challenging to accurately measure due to the very low abundance of the minor isotopes relative to 238 U, or 235 U in the case of highly enriched uranium (HEU). The goal of this project is to quantify detection limits for minor uranium isotope species at environmental levels (e.g 236 U/ 238 U < 10 -7 ) utilizing an ATONA-outfitted instrument and the Total Evaporation Thermal Ionization Mass Spectrometry (TE-TIMS) method. In the first half of Fiscal Year 2025, we set out to identify a suitable experimental material (Task 1) and to optimize our TE-TIMS measurement routine (Task 2). We have successfully identified a material and are in the process of getting an aliquot shipped to LANL. Simultaneously, we began working on our measurement routine utilizing CRM 112A. The results of each task are discussed in detail below.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Consistent $\overline{ν}$ evaluation for minor U isotopes with $\tt{CGMF}$

Following several successful prompt $\overline{ν}$ evaluations using $\tt{CGMF}$, including consistent evaluations for minor Pu isotopes, we detail in this report our efforts to perform a consistent $\overline{ν}$ evaluation for minor U isotopes during FY25. Although we have not yet produced a finalized evaluation, we present the progress that we have made towards such an evaluation for 232,233,234,236,237,239 U prompt $\overline{ν}$. Our milestone explicitly calls out evaluations for 233 U, 234 U, and 236 U, however, to better constrain the model with reliable experimental $\overline{ν}$ data, we also include 235 U and 238 U in the evaluation procedure. Then, we additionally produce evaluations for 232 U, 237 U and 239 U $\overline{ν}$ as a byproduct. Elsewhere, we will report our efforts on a stand-alone 233 U $\overline{ν}$ evaluation. This report is organized in the following manner. In Sec. 2, we briefly outline the updates to CGMF that were needed to be able to calculate all of these minor U fission reactions. The experimental data overview is given in Sec. 3. The evaluation methodology and results are presented in Secs. 4 and 5, respectively. Finally, we conclude and outline work for FY26 in Sec. 6.

07 ISOTOPE AND RADIATION SOURCES↗
NASA NTRS1975

Minor planets and comets in libration about the 2:1 resonance with Jupiter

We examine the orbits of minor planets in a search for objects librating about the 2:1 mean-motion resonance with Jupiter. Some 30 candidates are found among the Palomar-Leiden Survey and other unnumbered minor planets. Although almost all the orbits are very uncertain, there does seem to be an indication that librators of low orbital eccentricity do exist, contrary to the hypothesis by Giffen. We also tabulate data describing 12 comets that are temporarily librating about the 2:1 resonance. Finally, we present a discussion of what are apparently 'apocentric' librations. This type of libration, of which we find seven representatives among the numbered minor planets, can occur only for sufficiently small eccentricity. For such bodies, the role of Jupiter's eccentricity is vital; it is associated with a continuing alternation between apocentric libration and an oscillation of the line of apsides.

Franklin, F. A.↗
NASA NTRS1978

Travelling neutral disturbances and minor constituent particle mass

The mass cut-offs for critical or resonant coupling of minor species acoustic waves (so-called travelling neutral disturbances) and acoustic-gravity waves in the main atmosphere are shown and explained. The effects of vertical temperature gradients and the diffusion of the minor species on the mass cut-offs are also demonstrated. The wave characteristics of these minor species waves are examined. The wave number surface is shown to be such that energy and group velocity directions are more nearly vertical than those of gravity waves for the same phase velocity direction. It is expected that these coupled waves, when properly excited, will act to damp gravity waves and redistribute energy vertically. Implications for the thermosphere and mesosphere are discussed. Under ordinary conditions such resonant coupling is judged more likely for lighter mass species, such as helium and hydrogen.

Gross, S. H.↗
NASA NTRS1979

Transport of majority and minority carriers in 2-micron-diameter Pt-GaAs Schottky barriers

An experimental study of small area (2-micron diameter) Pt-GaAs Schottky barrier diodes has been made, by using a wafer chip with a matrix of these diodes lying within approximately a minority carrier diffusion length of one another. Using one diode as collector and another as emitter, transistor measurements indicated that the dominant contribution to the current is the majority-carrier thermionic field emission current for large forward-bias voltage of the emitter junction (V-EB no less than about 0.4 V), whereas the smaller forward-bias (V-EB no greater than about 0.4 V) recombination in the space-charge region was most important. The minority carrier injection ratio is measurable only for large forward-bias voltages, decreasing from about 0.02 to 0.00001 as VEB increases from 0.5 to 1.0 V. The minority carrier diffusion length was measured to be about 1.3 microns. These results are of considerable significance for the understanding and optimization of the performance of these devices as classical detectors and mixers.

Chan, E. Y.↗