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At least 109 records · Page 6

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NASA NTRS1972

Electron-beam-deposited thin polymer films - Electrical properties vs bombarding current.

Polymer films about 150 A thick, deposited on glass substrates by electron bombardment of tetramethyltetraphenyltrisiloxane, were studied, after being sandwiched between evaporated aluminum electrodes, the top one semitransparent. The capacitance, conductance, and photoconductance of the sandwiches were measured at room temperature as a function of the electron bombarding current which formed the polymer. The polymer thickness was obtained independently from Christy's (1960) empirical formula for the rate of formation. The obtained results indicate that, with increasing bombarding current, the polymer undergoes an increase in both crosslinking bonds and dangling bonds. Exposure to air drastically reduces the density of dangling bonds, but does not affect the crosslinking.

Babcock, L. E.↗

NASA NTRS1971

N-type mercury-cadmium-telluride photoconductors in optical heterodyne communication systems.

Discussion of the performance of a photoconductive (Hg,Cd)Te detector/mixer in a carbon dioxide laser heterodyne communication system. The utility of computer simulation of the performance of an optical heterodyne detector/mixer is demonstrated. Certain unusual properties of this device are pointed out that, while having a substantial impact on device performance, have received little previous attention.

Cohen, S. C.↗

NASA NTRS1972

Performance of S-192 /Hg,Cd/Te arrays.

Very high performance (Hg,Cd)Te photoconductive detectors have been fabricated for use on the S-192 experiment, which is a multispectral scanner being built by Honeywell for the NASA Manned Space Center's Skylab. The S-192 will scan the earth from Skylab and record data in twelve near infrared spectral bands and one long wavelength band. These detectors demonstrate good uniformity in performance across an array. State-of-the-art fabrication techniques have been used to make detectors with good definition that are 5-10 microns thick with 25-micron spacing between elements.

Aldrich, N. C.↗

NASA NTRS1972

N-Color /Hg,Cd/Te photodetectors.

N-color (Hg,Cd)Te photodetectors capable of spectral band analysis have been fabricated, tested, and delivered. This paper discusses the state of the art in (Hg,Cd)Te n-color photoconductive detectors. Included is a discussion of narrow band two-color devices responsive in the region of 8-14 microns. Preliminary results are also included for a unique three-color (Hg,Cd)Te device with cutoff wavelengths of 9.1, 10.8, and 13.8 microns.

Halpert, H.↗

NASA NTRS1974

Combined sun-acquisition and sun gate-sensor system for spacecraft attitude control

Arrangement combines acquisition and gate functions and reduces sensitivity so that attitude control is effective regardless of changes in solar intensity. There are five photoconductive detectors all electrically interconnected. Detectors are so positioned that, regardless of spacecraft orientation at any instant of interest, at least one detector is illuminated.

Schmidt, L. F.↗

NASA NTRS1972

High sensitivity infrared 10.6 micrometer heterodyne receiver development

The results are presented for a study on the design of an infrared 10.6-micrometer quantum-noise-limited optical receiver subsystem. Performance measurements of the HgCdTe photomixer preamplifier combination were carried out for photomixer temperatures up to 152 K and a photomixer frequency response of up to 420 MHz was obtained. Results of temperature and bias cycling of HgCdTe photomixers are reported. Design considerations for an operational 10.6 micrometer heterodyne receiver are presented. These consist of design data on required laser LO illumination, heat load levels for photomixer cooler, photomixer uniformity and the effects of photomixer impedance match on receiver sensitivity. Analysis and measurements of 10.6 micrometer heterodyne detection in an extrinsic photoconductive (p-type) HgCdTe photomixer are also presented.

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NASA NTRS1973

Methods of measurement for semiconductor materials, process control, and devices

This progress report describes NBS activities directed toward the development of methods of measurement for semiconductor materials, process control, and devices. Significant accomplishments during this reporting period include design of a plan to provide standard silicon wafers for four-probe resistivity measurements for the industry, publication of a summary report on the photoconductive decay method for measuring carrier lifetime, publication of a comprehensive review of the field of wire bond fabrication and testing, and successful completion of organizational activity leading to the establishment of a new group on quality and hardness assurance in ASTM Committee F-1 on Electronics. Work is continuing on measurement of resistivity of semiconductor crystals; characterization of generation-recombination-trapping centers in silicon; study of gold-doped silicon; development of the infrared response technique; evaluation of wire bonds and die attachment; and measurement of thermal properties of semiconductor devices, delay time and related carrier transport properties in junction devices, and noise properties of microwave diodes.

Bullis, W. M.↗

NASA NTRS1973

Photoconductor-metal contact at higher densities.

The formation of space charge in the barrier region is discussed. This region extends to a distance, x-sub o, equal to 200 A plus twice the mean free path of majority carriers. The conventional transport equation can be used only for x greater than x-sub o, and the carrier density at x-sub o represents a boundary condition for the bulk. Its change as a function of applied voltage, temperature, and light intensity in photoconducting CdS is discussed. The time dependence of the space-charge formation in the region between 0 and x-sub o is analyzed. It is shown under which conditions the individuality of the metal contact is observable.

Dussel, G. A.↗

NASA NTRS1974

Specific wavelength colorimeter

A self contained, specific wavelength, single beam colorimeter is described for direct spectrophotometric measurement of the concentration of a given solute in a test sample. An electrical circuit employing a photoconductive cell converts the optical output into a linear, directly readable meter output. The colorimeter is simple to operate and is adapted for use in zero gravity conditions. In a specific application, the colorimeter is designed to analyze the concentration of iodine in potable water carried aboard a space vehicle such as the 4B stage of Skylab.

Brawner, C. C.↗

NASA NTRS1973

Real-time incoherent-to-coherent optical converter

Description of a real-time incoherent-to-coherent optical converter designed for application in image processing systems. The converter utilizes the photoconductivity effect of the compound Bi(12)SiO(20) for spatial modulation of electrical polarization in the compound. An optically absorbed write-in image is stored as an image polarization pattern in the device. Readout is effectuated electrooptically by using phase retardation in a polarized coherent light beam during the passage through the crystal. The operating mode required for achieving continuous image conversion with a high-speed recyclability is discussed. The performance characteristics of the converter are given and the fabrication technology is described.

Vohl, P.↗

NASA NTRS1975

Read-only optical storage medium

Photosensitive recording medium consists of thin-film silicone resin deposited on photoconductive substrate. Medium is useful for holographic interferometry studies.

Gange, R. A.↗

NASA NTRS1974

LK21T1 S/N V-3 infrared detector

An infrared detector was fabricated to determine the feasibility of atmospheric sounding from synchronous orbit for water vapor and carbon dioxide. The device was extensively tested both before and after a 24-hour soak at 50 C and relative humidity of 95 percent. No degradation in performance as a result of the soak was observed. The device contains a single photoconductive HgCdTe element designed to operate in the six to fifteen micron region.

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NASA NTRS1975

Detection of the O III 88.16-micron forbidden line in M17

This paper reports the detection of the fine-structure forbidden line of O III at 88.16 microns in emission from M 17 (the Omega Nebula), which is an optically bright galactic H II region and a strong thermal radio source. The observations were made using an airborne 30-cm telescope and a liquid helium-cooled grating spectrometer with Ge:Ga photoconductive detectors. The line intensity is found to be 2.2 (+1.0, -0.7) by 10 to the -15th power W/sq cm. The results are compared with those of a search for the present line in M 42 as well as with theoretical predictions of the line intensity.

Ward, D. B.↗

NASA NTRS1975

Electron and proton damage coefficients in low-resistivity silicon

The electron and proton damage coefficients for low resistivity p-type boron-doped silicon were determined from minority-carrier lifetime measurements on bulk material and diffusion length measurements on solar cells. The bulk samples were irradiated with electrons at three energy levels (0.5, 1.5, and 2.5 MeV) using a Dynamitron. Lifetime measurements were made with a steady-state photoconductivity apparatus, and comparison measurements of diffusion length were obtained using the steady-state surface photovoltage method (Goodman, 1961). The diffusion-length damage coefficients increased with decreasing resistivity for boron-doped silicon; this dependence can be qualitatively accounted for using a two-level Hall-Shockley-Read model. The damage coefficients for solar cells were larger than for their bulk-material counterparts. The damage coefficient was apparently independent of the dislocation density in the 0.1 ohm-cm bulk samples and solar cells investigated.

Srour, J. R.↗

NASA NTRS1976

A CCD scanned (Hg, Cd)Te array for earth viewing applications

A 9 channel demonstration of 10 micrometer photoconductive mercury cadmium telluride detector array, bipolar preamplifiers, and a Si CCD multiplexer, integrated into a focal plane assembly and operating at 105 K and at 17 Hz is reported. The result of a direct coupling experiment between a 5-micrometer photovoltaic mercury cadmium telluride photodiode and a CCD is revealed. No appreciable degradation in the signal-to-noise ratio was experienced.

Iwasa, S.↗

NASA NTRS1977

Liquid helium-cooled MOSFET preamplifier for use with astronomical bolometer

A liquid helium-cooled p-channel enhancement mode MOSFET, the 3N167, is found to have sufficiently low noise for use as a preamplifier with helium-cooled bolometers that are used in infrared astronomy. Its characteristics at 300, 77, and 4.2 K are presented. It is also shown to have useful application with certain photoconductive and photovoltaic infrared detectors.

Goebel, J. H.↗

NASA NTRS1979

A solid-state phase-insensitive ultrasonic transducer

Photoconductive acoustoelectric transducer (AET) functions as phase-insensitive ultrasonic transducer. Device is easy to use and requires no additional noisy components such as light or thermal source.

Heyman, J. S.↗

NASA NTRS1977

Multilayered (Hg,Cd)Te infrared detector

Multilayered mercury-cadmium telluride photoconductive detectors were developed which are capable of providing individual coverage of three separate spectral wavelength bands without the use of beam splitters. The multilayered "three-color" detector on a single dewar takes the place of three separate detector/filter/dewar units and enables simpler and more reliable mechanical and optical designs for multispectral scanners and radiometers. Wavelength channel design goals (in micrometers) were: 10.1 to 11.0, 11.0 to 12.0, and 13.0. Detectivity for all channels was 1 x 10 to the 10th power cm-Hz 1/2/Watt. A problem occurred in finding an epoxy layer which had good infrared transmission properties and which also was chemically and mechanically compatible with HgCdTe processing techniques. Data on 6 candidate bonding materials are surveyed and discussed.

Rae, W. G.↗