Weak Gravitational Lensing in the Laboratory: Status Update to Weak Lensing Science GREAT-10 Meeting
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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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Tunneling effects in the current-voltage characteristics of high-efficiency GaAs solar cells
Evidence is that tunneling via states in the forbidden gap is the dominant source of excess current in the dark current-voltage (I-V) characteristics of high-efficiency DMCVD grown Al(x)Ga(1-x)As/GaAs(x is equal to or greater than 0.85) solar cells. The dark forward and reverse I-V measurements were made on several solar cells, for the first time, at temperatures between 193 and 301 K. Low-voltage reverse-bias I-V data of a number of cells give a thermal activation energy for excess current of 0.026 + or - 0.005 eV, which corresponds to the carbon impurity in GaAs. However, other energy levels between 0.02 eV and 0.04 eV were observed in some cells which may correspond to impurity levels introduced by Cu, Si, Ge, or Cd. The forward-bias excess current is mainly due to carrier tunneling between localized levels created in the space-charge layer by impurities such as carbon, which are incorporated during the solar cell growth process. A model is suggested to explain the results.
Kachare, R.↗
Low dark current photovoltaic multiquantum well long wavelength infrared detectors
The authors have, for the first time, demonstrated photovoltaic detection for an multiple quantum well (MQW) detector. With a blocking layer, the MQW detector exhibits Schottky I-V characteristics with extremely low dark current and excellent ideality factor. The dark current is 5 times 10(exp -14) A for an 100x100 square micron 10 micron detector at 40 K, 8 to 9 orders of magnitude lower than that of a similar 10 micron MQW detector without blocking layer. The ideality factor is about 1.01 to 1.05 at T = 40 to 80 K. The measured barrier height is consistent with the energy difference between first excited states and ground states, or the peak of spectral response. The authors also, for the first time, report the measured effective Richardson constant (A asterisk asterisk) for the GaAs/AlGaAs heterojunction using this blocking layer structure. The A asterisk asterisk is low approx. 2.3 A/sq cm/K(exp 2).
Wu, C. S.↗
A Highly Sensitive Multi-Element HgCdTe E-APD Detector for IPDA Lidar Applications
An HgCdTe electron avalanche photodiode (e-APD) detector has been developed for lidar receivers, one application of which is integrated path differential absorption lidar measurements of such atmospheric trace gases as CO2 and CH4. The HgCdTe APD has a wide, visible to mid-wave-infrared, spectral response, high dynamic range, substantially improved sensitivity, and an expected improvement in operational lifetime. A demonstration sensor-chip assembly consisting of a 4.3 lm cutoff HgCdTe 4 9 4 APD detector array with 80 micrometer pitch pixels and a custom complementary metal-oxide-semiconductor readout integrated circuit was developed. For one typical array the APD gain was 654 at 12 V with corresponding gain normalized dark currents ranging from 1.2 fA to 3.2 fA. The 4 9 4 detector system was characterized at 77 K with a 1.55 micrometer wavelength, 1 microsecond wide, laser pulse. The measured unit gain detector photon conversion efficiency was 91.1%. At 11 V bias the mean measured APD gain at 77 K was 307.8 with sigma/mean uniformity of 1.23%. The average, noise-bandwidth normalized, system noise-equivalent power (NEP) was 1.04 fW/Hz(exp 1/2) with a sigma/mean of 3.8%. The measured, electronics-limited, bandwidth of 6.8 MHz was more than adequate for 1 microsecond pulse detection. The system had an NEP (3 MHz) of 0.4 fW/Hz(exp 1/2) at 12 V APD bias and a linear dynamic range close to 1000. A gain-independent quantum-limited SNR of 80% of full theoretical was indicative of a gain-independent excess noise factor very close to 1.0 and the expected APD mode quantum efficiency.
NEP↗
Radiation effects in Ga(0.47)In(0.53)As solar cells
The effects of irradiating Ga(0.47)In(0.53)As p-i-n junctions with 1 MeV electrons were measured using Deep Level Transient Spectroscopy (DLTS) and both dark and illuminated (1 sun, air mass zero (AM0)) current-voltage (I-V) measurements. The I-V measurements were made over the range 100K less than T less than 350K. Temperature coefficients of the Ga(0.47)In(0.53)As photovoltaic parameters are presented which follow the same general behavior as other solar cell materials (e.g. Si and GaAs). Fits of the dark I-V data to the two term diode equation before irradiation were satisfactory, yielding an estimated band-gap energy of 0.79 eV. The recombination component of the dark current was found to increase linearly with fluence. DLTS detected two radiation-induced defect levels one shallow (E(sub c)-0.10 eV) and one near mid-gap (E(sub c)-0.29 eV), and it is the near mid-gap level which is expected to be the cause of the dark current increase. The radiation-induced degradation of the open circuit voltage is shown to be accurately predicted from the dark I-V measurements. The degradation of the open circuit voltage dominated the radiation response of the photovoltaic parameters while the short circuit current was only moderately degraded. This behavior is qualitatively explained in terms of the base thickness and dopant level. Appropriate changes in the device structure are suggested which should increase the radiation resistance. Isochronal thermal annealing induced recovery in the photovoltaic parameters at approximately 400K, coinciding with an annealing stage of the near mid-gap defect level.
Walters, R. J.↗
Improved Si:As BIBIB (Back-Illuminated Blocked-Impurity-Band) hybrid arrays
Results of a program to increase the short wavelength (less than 10 microns) detective quantum efficiency, eta/beta, of Si:As Impurity Band Conduction arrays are presented. The arrays are epitaxially grown Back-Illuminated Blocked (BIB) Impurity-Band (BIBIB) 10x50 detectors bonded to switched-FET multiplexers. It is shown that the 4.7 microns detective quantum efficiency increases proportionately with the thickness of the infrared active layer. A BIB array with a thick active layer, designed for low dark current, exhibits eta/beta = 7 to 9 percent at 4.7 microns for applied bias voltages between 3 and 5 V. The product of quantum efficiency and photoelectric gain, etaG, increases from 0.3 to 2.5 as the voltage increases from 3 to 5 V. Over this voltage range, the dark current increases from 8 to 120 e(-)s(-1) at a device temperature of 4.2 K and is under 70 e(-)s(-1) for all voltages at 2 K. Because of device gain, the effective dark current (equivalent photon rate) is less than 3 e(-)s(-1) under all operating conditions. The effective read noise (equivalent photon noise) is found to be less than 12 electrons under all operating conditions and for integration times between 0.05 and 100 seconds.
Herter, T.↗
SAS 3 and related observations of Abell 2029
X-ray and radio observations of the cluster of galaxies show that the central cD galaxy dominates the emissions. Resolution of the X-ray source shows that its extent is significantly greater than that of the profile of surface brightness of the cD galaxy. Dressler's model of most of the cluster mass with very high M/L(v) is similarly extended. The optically dark mass may provide low-energy X-ray emission of the coronae of 5 x 10 to the 16th stars with very high M/L(v), but in the 2-10 keV range the data are consistent with current theoretical predictions for hot intracluster gas.
Johnson, H. M.↗
Survey of the BY Draconis syndrome among dMe stars
Results are reported for a BVr photometric survey of 22 dK, dKe, dM, and dMe stars conducted to search for slow quasi-sinusoidal fluctuations in V (the BY Draconis syndrome). The (B-V) and (V-r) color indices are determined in an attempt to detect wavelength-dependent color changes produced by starspots and to infer starspot temperatures. It is found that nine of the stars exhibit variations in V of the order of 0.05 to 0.10 magnitude on a time scale of days or weeks, that at least three more display changes in mean light level over a period of years, that the stars generally tend to become redder at minimum light, and that some of the stars show no detectable color changes over their photometric cycle. The color data are taken to suggest a probable temperature difference of about 200 to 500 K between the stellar photospheres and starspots if the V variations are attributed to dark spots. It is concluded that the BY Draconis syndrome is clearly a very common occurrence among dMe stars.
Bopp, B. W.↗
Effect of copper impurity on polycrystalline silicon solar cells
The presence of copper impurity, up to 10 to the 15th atoms/cc, in single crystal silicon has been shown to have no deleterious effect on the p-n junction solar cell performance. However, in polycrystalline silicon, copper atoms tend to migrate to the defect sites because of the structural sensitive properties of copper. This study was undertaken to investigate the influence of this behavior of copper impurity on the performance of p-n junction solar cells fabricated from structurally imperfect silicon. Two sets of polycrystalline silicon substrates containing copper were examined. In one set of samples, copper was incorporated during growth, whereas in the other, copper was diffused. Solar cells were fabricated on both the sets of substrates by a standard process. Dark and light I-V and spectral response characteristics of the cells were measured and compared with copper-free polycrystalline silicon solar cells. The results and the model are discussed.
Daud, T.↗
Radiation damage of gallium arsenide production cells
High efficiency liquid phase epitaxy (LPE) gallium arsenide cells were irradiated with 1 Mev electrons up to fluences of 1 times 10 to the 16th power cm-2. Measurements of spectral response and dark and illuminated I-V data were made at each fluence and then, using computer codes, the experimental data was fitted to gallium arsenide cell models. In this way it was possible to determine the extent of the damage, and hence damage coefficients in both the emitter and base of the cell.
Mardesich, N.↗
Effects of illumination on the conductivity properties of spacecraft insulating materials
Experimental data on the dark and illuminated conductivities of Kapton V and polyvinylidene fluoride (PVF2) films are described as well as the changes in insulating properties produced in Kapton H, Kapton V, PVF2, and FEP Teflon films as result of prolonged exposure to solar illumination. An overall summary of the results of tests is presented. A general introduction and a description of the experimental apparatus and procedures used are also given.
Adamos, R. C.↗
Method of mitigating titanium impurities effects in p-type silicon material for solar cells
Microstructural evaluation tests performed on Cu-doped, Ti-doped and Cu/Ti doped p-type silicon single crystal wafers, before and after the solar cell fabrication, and evaluation of both dark forward and reverse I-V characteristic records for the solar cells produced from the corresponding silicon wafers, show that Cu mitigates the unfavorable effects of Ti, and thus provides for higher conversion efficiency, thereby providing an economical way to reduce the deleterious effects of titanium, one of the impurities present in metallurgical grade silicon material.
Salama, A. M.↗
A catalog of red stars near L1454
In view of their potential interest as individual objects of study, a catalog is presented of stars noted by the Duerr and Craine (1982) study of the nature of the dark cloud L1454 to have V-I magnitudes greater than about 2.5. Finding charts are given for these 156 stars, with attention to the individual quadrants of the region studied. The original star counts had been made with Near Infrared Photographic Sky Survey data.
Duerr, R.↗
Multiplexed 256 element InGaAs detector arrays for 0.8-1.7-micron room-temperature operation
InGaAs photodetectors have been configured into linear arrays of 30 x 30 micron photodetectors spaced 50 microns apart. The devices have typical responsivities of 0.9 A/W (86-percent QE) at 1.3 microns and exhibit room temperature dark currents below 100 pA. A 256-element array has been mounted in a Reticon multiplexer and configured into a PAR optical multichannel analyzer to extend spectral response out to 1.7 microns. Individual InGaAs detectors have been fabricated for response out to 2.2 microns with dark current below 1 microA (-1V) and 50-percent QE at room temperature.
Olsen, G. H.↗
Palagonitic Mars from Rock Rinds to Dust: Evidence from Visible, Near-IR, and Thermal Emission Spectra of Poorly Crystalline Materials
Visible and near-IR (VNIR) spectral data for Martian bright regions are characterized by a general shape consisting of a ferric absorption edge extending from about 400 to 750 nm and relatively constant reflectivity extending from about 750 nm to beyond 2000 nm . Among terrestrial geologic materials, the best spectral analogues are certain palagonic tephras from Mauna Kea Volcano (Hawaii). By definition, palagonite is a yellow or orange isotropic mineraloid formed by hydration and devitrification of basaltic glass. The ferric pigment in palagonite is nanometer-sized ferric oxide particles (np-Ox) dispersed throughout the hydrated basaltic glass matrix. The hydration state of the np-Ox particles is not known, and the best Martian spectral analogues contain allophane-like materials and not crystalline phyllosilicates. We show here that laboratory VNIR and TES spectra of palagonitic alteration rinds developed on basaltic rocks are spectral endmembers that provide a consistent explanation for both VNIR and TES data of Martian dark regions.
Morris, R. V.↗
Palagonitic Mars: A Basalt Centric View of Surface Composition and Aqueous Alteration
Palagonitic tephra from certain areas on Mauna Kea Volcano (Hawaii) are well-established spectral and magnetic analogues of high-albedo regions on Mars. By definition, palagonite is "a yellow or orange isotropic mineraloid formed by hydration and devitrification of basaltic glass." The yellow to orange pigment is nanometer-sized ferric oxide particles (np-Ox) dispersed throughout the hydrated basaltic glass matrix. The hydration state of the np-Ox particles and the matrix is not known, but the best Martian spectral analogues contain allophane-like materials and not crystalline phyllosilicates. Martian low-albedo regions are also characterized by a palagonite-like ferric absorption edge, but, unlike the highalbedo regions, they also show evidence for absorption by ferrous iron. Thermal emission spectra (TES) obtained by the Mars Global Surveyor Thermal Emission Spectrometer suggest that basaltic (surface Type 1) and andesitic (surface Type 2) volcanic compositions preferentially occur in southern (Syrtis Major) and northern (Acidalia) hemispheres, respectively. The absence of a ferric-bearing component in the modeling of TES spectra is in apparent conflict with VNIR spectra of Martian dark regions, as discussed above. However, the andesitic spectra have also been interpreted as oxidized basalt using phyllosilicates instead of high-SiO2 glass as endmembers in the spectral deconvolution of surface Type 2 TES spectra. We show here that laboratory VNIR and TES spectra of rinds on basaltic rocks are spectral endmembers that provide a consistent explanation for both VNIR and TES data of Martian dark regions.
Morris, R. V.↗
SWUIS-A: A Versatile, Low-Cost UV/VIS/IR Imaging System for Airborne Astronomy and Aeronomy Research
We have developed and successfully flight-tested on 14 different airborne missions the hardware and techniques for routinely conducting valuable astronomical and aeronomical observations from high-performance, two-seater military-type aircraft. The SWUIS-A (Southwest Universal Imaging System - Airborne) system consists of an image-intensified CCD camera with broad band response from the near-UV to the near IR, high-quality foreoptics, a miniaturized video recorder, an aircraft-to-camera power and telemetry interface with associated camera controls, and associated cables, filters, and other minor equipment. SWUIS-A's suite of high-quality foreoptics gives it selectable, variable focal length/variable field-of-view capabilities. The SWUIS-A camera frames at 60 Hz video rates, which is a key requirement for both jitter compensation and high time resolution (useful for occultation, lightning, and auroral studies). Broadband SWUIS-A image coadds can exceed a limiting magnitude of V = 10.5 in <1 sec with dark sky conditions. A valuable attribute of SWUIS-A airborne observations is the fact that the astronomer flies with the instrument, thereby providing Space Shuttle-like "payload specialist" capability to "close-the-loop" in real-time on the research done on each research mission. Key advantages of the small, high-performance aircraft on which we can fly SWUIS-A include significant cost savings over larger, more conventional airborne platforms, worldwide basing obviating the need for expensive, campaign-style movement of specialized large aircraft and their logistics support teams, and ultimately faster reaction times to transient events. Compared to ground-based instruments, airborne research platforms offer superior atmospheric transmission, the mobility to reach remote and often-times otherwise unreachable locations over the Earth, and virtually-guaranteed good weather for observing the sky. Compared to space-based instruments, airborne platforms typically offer substantial cost advantages and the freedom to fly along nearly any groundtrack route for transient event tracking such as occultations and eclipses.
Durda, Daniel D.↗
Gene activity during germination of spores of the fern, Onoclea sensibilis: RNA and protein synthesis and the role of stored mRNA
Pattern of 3H-uridine incorporation into RNA of spores of Onoclea sensibilis imbibed in complete darkness (non-germinating conditions) and induced to germinate in red light was followed by oligo-dT cellulose chromatography, gel electrophoresis coupled with fluorography and autoradiography. In dark-imbibed spores, RNA synthesis was initiated about 24 h after sowing, with most of the label accumulating in the high mol. wt. poly(A) -RNA fraction. There was no incorporation of the label into poly(A) +RNA until 48 h after sowing. In contrast, photo-induced spores began to synthesize all fractions of RNA within 12 h after sowing and by 24 h, incorporation of 3H-uridine into RNA of irradiated spores was nearly 70-fold higher than that into dark-imbibed spores. Protein synthesis, as monitored by 3H-arginine incorporation into the acid-insoluble fraction and by autoradiography, was initiated in spores within 1-2 h after sowing under both conditions. Autoradiographic experiments also showed that onset of protein synthesis in the cytoplasm of the germinating spore is independent of the transport of newly synthesized nuclear RNA. One-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis of 35S-methionine-labelled proteins revealed a good correspondence between proteins synthesized in a cell-free translation system directed by poly(A) +RNA of dormant spores and those synthesized in vivo by dark-imbibed and photo-induced spores. These results indicate that stored mRNAs of O. sensibilis spores are functionally competent and provide templates for the synthesis of proteins during dark-imbibition and germination.
NASA Discipline Number 29-20↗