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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Long-Wavelength-Infrared Hot-Electron Transistor

Dark current reduced by energy-discriminating quantum filter. Very long-wavelength-infrared hot-electron transistor developed. Device detects photons at wavelengths around 16 micrometers. Comprises photodector integrated with energy-discriminating quantum filter in multiple-quantum-well structure. Made of variously doped and undoped layers of GaAs (quantum wells) and Al(x)Ga(1-x)As (barriers between wells). In transistor, bound-to-continuum GaAs/Al(x)Ga(1-x)As multiple-quantum-well infrared photodectors (QWIP) serves as photosensitive emitter. Wide quantum well serves as base, and there is thick barrier between base and collector. Combination of barrier and base quantum well acts as energy-discriminating filter: electrons with higher energies pass through filter to collector, those with lower energies blocked and diverted from output-current path through base contact.

Gunapala, Sarath D.↗
NASA NTRS1995

In(x)Ga(1-x)As/GaAs Quantum-Well Infrared Photodetectors

Choice of materials for present quantum-well infrared photodetectors (QWIPs) affected principally by two considerations. One was that in comparison with GaAs, In(x)Ga(1-x)As is potentially superior quantum-well material because of its stronger absorption of infrared radiation. Other consideration was that in comparison with Al(x)Ga(1-x)As, which is usual barrier material in older devices, GaAs potentially superior barrier material because it exhibits superior transport properties (lower scattering and higher mobility of charge carriers). GaAs is well material in older devices and barrier material in present devices.

Gunapala, Sarath D.↗
NASA NTRS1997

15-micro-m 128 x 128 GaAs/Al(x)Ga(1-x) As Quantum Well Infrared Photodetector Focal Plane Array Camera

In this paper, we discuss the development of very sensitive, very long wavelength infrared GaAs/Al(x)Ga(1-x)As quantum well infrared photodetectors (QWIP's) based on bound-to-quasi-bound intersubband transition, fabrication of random reflectors for efficient light coupling, and the demonstration of a 15 micro-m cutoff 128 x 128 focal plane array imaging camera. Excellent imagery, with a noise equivalent differential temperature (N E(delta T)) of 30 mK has been achieved.

Gunapala, Sarath D.↗
NASA NTRS2000

"Genetically Engineered" Nanoelectronics

The quantum mechanical functionality of nanoelectronic devices such as resonant tunneling diodes (RTDs), quantum well infrared-photodetectors (QWIPs), quantum well lasers, and heterostructure field effect transistors (HFETs) is enabled by material variations on an atomic scale. The design and optimization of such devices requires a fundamental understanding of electron transport in such dimensions. The Nanoelectronic Modeling Tool (NEMO) is a general-purpose quantum device design and analysis tool based on a fundamental non-equilibrium electron transport theory. NEW was combined with a parallelized genetic algorithm package (PGAPACK) to evolve structural and material parameters to match a desired set of experimental data. A numerical experiment that evolves structural variations such as layer widths and doping concentrations is performed to analyze an experimental current voltage characteristic. The genetic algorithm is found to drive the NEMO simulation parameters close to the experimentally prescribed layer thicknesses and doping profiles. With such a quantitative agreement between theory and experiment design synthesis can be performed.

Klimeck, Gerhard↗
NASA NTRS2000

Characterization of Thermal Parameters for Improving Pyranometer and Pyrgeometer Measurements

Since the introduction of thermopile, pyranometers (solar, e.g., 0.3-3.0 micrometers) and pyrgeometers (terrestrial, e.g., 4-50 micrometers) have become instruments commonly used for measuring the broadband hemispherical irradiances at the surface in a long-term, monitoring mode for decades. These commercially available radiometers have been manufactured in several countries such as from the United States, Asia, and Europe, and are generally reliable and economical. These worldwide distributions of surface measurements become even more important in the era of Earth remote sensing in studying climate change. However, recent studies from field campaigns have pointed out that erroneous factors (e.g., temperature gradients between the filter dome and detector, emissivity of the thermopile) are responsible for the unacceptable level of uncertainty (e.g., 20 W m(exp -2)). Using a newly developed instrument of Quantum Well Infrared Photodetector (QWTP), we have characterized the brightness temperature fields of pyranometers and pyrgeometers under various sky conditions. The QWIP is based on the superlattice (GaAs/AlGaAs) technology and has a noise equivalent temperature (NEAT) less than 0.1 K. The quality of pyranometer and pyrgeometer measure- ments can be improved largely by applying proper knowledge of the thermal parameters affecting the operation of the thermopile systems. Data correction procedure and algorithm will be presented and discussed.

Tsay, Si-Chee↗
NASA NTRS2002

Development of a 4-15 micron Infrared GaAs Hyperspectral QWlP Imager (HQI)

A viewgraph presentation on the development of a 4-15 micron Infrared GaAs Hyperspectral QWIP Imager (HQI) is provided. The topics include: 1) Background and Project Goals; 2) Instrument Overview; 3) Subassembly Description; 4) Operating Conditions; 5) Current System Performance Status; and 6) Near-Term Improvements.

Jhabvala, M.↗
NASA NTRS2004

THIS: A Next Generation Tuneable Heterodyne Infrared Spectrometer for SOFIA

A new infrared heterodyne instrument has been developed which allows the use of both tuneable diode lasers (TDL) and quantum cascade lasers (QCL) as local oscillators (LO). The current frequency tuning range of our system extends from 900 to 1100/cm depending on the availability of lasers but is planned to be extended to 600/cm soon. The IF-bandwidth is 1.4 GHz using an acousto-optical spectrometer (AOS). The frequency resolution and stability of the system is approximately 10(exp 7). Currently, mercury-cadmium-telluride (MCT) detectors are used as mixers while new devices like quantum-well-infrared-photodetectors (QWIP) and hot-electron-bolometers (HEB) are investigated. The IF-bandwidth can be extended to about 3 GHz by using a new broadband acousto-optical spectrometer presently under development. The instrument is fully transportable and can be attached to any infrared or optical telescope. The semiconductor laser is stabilized to a Fabry-Perot ring-resonator, which is also used as an efficient diplexer to superimpose the local-oscillator and the signal radiation. As a first step measurements of trace gases in Earth's atmosphere and non-LTE emission from Venus' atmosphere were carried out as well as observations of molecular features in sunspots. Further astronomical observations from ground-based telescopes and the airborne observatory SOFIA are planned for the future. Of particular interest are molecules without a permanent dipole moment like H2, CH4, C2H2 etc.

Sonnabend, Guido↗
NASA NTRS2002

Multi-band quantum well infrared photodetectors

The GaAs/AlGaAs based Quantum Well Infrared Photodetectors (QWIPs) afford greater flexibility than the usual extrinsically doped semiconductor IR detectors because the wavelength of the peak response and cutoff can be continuously tailored over any wavelength between 6-20 mu m.

IR quantum well thermal imaging multi-spectral↗
NASA NTRS2000

Quantum Well Infrared Photodetectors for low background application

QWIPs operate by photoexcitation of electrons between ground and first excited state subbands of multi-quantum wells (MQWs) which are artificially fabricated by placing thin layers of two dfferent, high-bandgap semiconductor materials alternately. The bandgap discontinuity of two materials creates quantized subbands in the potential wells associated with conduction bands.

infrared focal plane arrays quantum wells↗
NASA NTRS1996

Long Wavelength 256 X 256 Quantum Well Infrared Photodetector Portable Camera

In this paper, we discuss the development of very sensitive long wavelength infrared (LWIR) GaAs/AlGal-xAs Quantum well infrared photodetectors (QWIPS), fabrication of random reflectors for efficient light coupling, and the demonstration of a LWIR 256 X 256 focal plane array imaging camera. Excellent imagery, with a noise equivalent differential temperature (NE-delta-T) of 25 mK has been achieved.

long wavelength inrared photodetectors random refl↗
NASA NTRS1995

15m 128x128 Quantum Well Infrared Photodetector Focal Plane Array Camera

We have developed a first generation 15 GaAs/AlGaAs 128x128 quantum well infrared photodetectors (QWIPSs) focal plane array (FPA) for a staring infrared (IR) sensor system. The photoconductive QWIPs of the 128x128 FPAs were then fabricated by wet chemical etching through the photosensitive GaAs/AlGaAs multi quantum well layers into the 1 thick doped GaAs contact layer. The pitch of the FPA is 50 m and the actual pixel size is 38x38m2.

Infrared Photodetector↗
NASA NTRS2007

A 640 X 512-Pixel Portable Long-Wavelength Infrared Camera

A portable long-wavelength infrared electronic camera having a cutoff wavelength of 9 microns has been built around an image sensor in the form of a 640X512-pixel array of AlxGa(1-x)As/GaAs quantum-well infrared photodetectors (QWIPs). This camera is an intermediate product of a continuing program to develop high-resolution, high-sensitivity infrared cameras.

Gunapala, Sarath↗
NASA NTRS2007

NASA Tech Briefs, August 2007

Topics include: Program Merges SAR Data on Terrain and Vegetation Heights; Using G(exp 4)FETs as a Data Router for In-Plane Crossing of Signal Paths; Two Algorithms for Processing Electronic Nose Data; Radiation-Tolerant Dual Data Bus; General-Purpose Front End for Real-Time Data Processing; Nanocomposite Photoelectrochemical Cells; Ultracapacitor-Powered Cordless Drill, Cumulative Timers for Microprocessors; Photocatalytic/Magnetic Composite Particles; Separation and Sealing of a Sample Container Using Brazing; Automated Aerial Refueling Hitches a Ride on AFF; Cobra Probes Containing Replaceable Thermocouples; High-Speed Noninvasive Eye-Tracking System; Detergent-Specific Membrane Protein Crystallization Screens; Evaporation-Cooled Protective Suits for Firefighters; Plasmonic Antenna Coupling for QWIPs; Electronic Tongue Containing Redox and Conductivity Sensors; Improved Heat-Stress Algorithm; A Method of Partly Automated Testing of Software; Rover Wheel-Actuated Tool Interface; and Second-Generation Electronic Nose.

Source record↗
NASA NTRS2010

High-Speed Operation of Interband Cascade Lasers

Optical sources operating in the atmospheric window of 3-5 microns are of particular interest for the development of free-space optical communication link. It is more advantageous to operate the free-space optical communication link in 3-5-microns atmospheric transmission window than at the telecom wavelength of 1.5 m due to lower optical scattering, scintillation, and background radiation. However, the realization of optical communications at the longer wavelength has encountered significant difficulties due to lack of adequate optical sources and detectors operating in the desirable wavelength regions. Interband Cascade (IC) lasers are novel semiconductor lasers that have a great potential for the realization of high-power, room-temperature optical sources in the 3-5-microns wavelength region, yet no experimental work, until this one, was done on high-speed direct modulation of IC lasers. Here, highspeed interband cascade laser, operating at wavelength 3.0 m, has been developed and the first direct measurement of the laser modulation bandwidth has been performed using a unique, highspeed quantum well infrared photodetector (QWIP). The developed laser has modulation bandwidth exceeding 3 GHz. This constitutes a significant increase of the IC laser modulation bandwidth over currently existing devices. This result has demonstrated suitability of IC lasers as a mid-IR light source for multi-GHz free-space optical communications links

Soibel, Alexander↗
NASA NTRS2011

The Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS) on the Landsat Data Continuity Mission (LDCM)

The Landsat Data Continuity Mission (LDCM), a joint NASA and United States Geological Survey (USGS) mission, is scheduled for launch in December, 2012. The LDCM instrument payload will consist of the Operational Land Imager (OLI), provided by Ball Aerospace and Technology Corporation (BATC) under contract to NASA and the Thermal Infrared Sensor (TIRS), provided by NASA's Goddard Space Flight Center (GSFC). This paper will describe the design, capabilities and status of the OLI and TIRS instruments. The OLI will provide 8 channel multispectral images at a spatial resolution of 30 meters and panchromatic images at 15 meter spatial resolution. The TIRS is a 100 meter spatial resolution push-broom imager whose two spectral channels, centered at 10.8 and 12 microns, split the ETM+ thermal bands. The two channels allow the use of the "split-window" technique to aid in atmospheric correction. The TIRS focal plane consists of three Quantum Well Infrared Photodetector (QWIP) arrays to span the 185 km swath width. The OLI and TIRS instruments will be operated independently but in concert with each other. Data from both instruments will be merged into a single data stream at the (USGS)/Earth Resources Observation and Science (EROS) facility. The ground system, being developed by USGS, includes an Image Assessment System (lAS), similar to Landsat-7's, to operationally monitor, characterize and update the calibrations of the two sensors.

Reuter, Dennis↗