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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Semiconductor lasers for space sensor applications

Despite their intrinsic power limitations, semiconductor laser diodes are essential for laser-based spaceborne sensor systems covering a wide spectral range, fulfilling such roles as pumping and injection-locking. They may also be used as direct sources in shorter-range operations. AlGaAs laser arrays have been developed for 810-nm band pumping in Nd:YAG lasers otherwise emitting at 1.064 nm. Additional roles include their use as low-power injection seeds, locking a solid-state laser into a specific desired wavelength.

Katz, Joseph↗
NASA NTRS1987

Analysis of the fluid dynamics and heat transfer during micro-gravity Bridgman-Stockbarger growth of semiconductors in steady periodic gravitational fields

The effect of periodic variations in the magnitude and direction of gravitational acceleration on buoyancy-driven convection in the melt during microgravity growth of low Prandtl number semiconductor materials in Brigdman-Stockbarger configuration is investigated through the numerical solution of the transient Navier-Stokes and energy equations. Results are presented over a wide range of Rayleigh numbers and frequency spectrum of periodic g-level variations corresponding to conditions present on earth and on board spacecrafts. The frequency response of convection in the melt during growth is found to be similar to that of a first order dynamic system with a cutoff frequency determined by the diffusion of momentum in the system. Results indicate that during growth of small diameter Germanium crystals, convection in the melt is insensitive to the measured g-gitter on board the shuttle.

Griffin, Patrick R.↗
NASA NTRS1989

Increasing And Combining Outputs Of Semiconductor Lasers

Paper reviews methods of increasing and combining outputs of semiconductor lasers, with references to literature of recent years (mostly 1986 and 1987). This is a field of great practical importance: Necessary to increase or combine outputs of individual lasers to obtain sufficient power for such uses as communication, ranging, remote sensing, printing, and pumping solid-state lasers.

Katz, Joseph↗
NASA NTRS1989

Spinner For Etching Of Semiconductor Wafers

Simple, inexpensive apparatus coats semiconductor wafers uniformly with hydrofluoric acid for etching. Apparatus made in part from small commercial electric-fan motor. Features bowl that collects acid. Silicon wafer placed on platform and centered on axis; motor switched on. As wafer spins, drops of hydrofluoric acid applied from syringe. Centrifugal force spreads acid across wafer in fairly uniform sheet.

Lombardi, Frank↗
NASA NTRS1989

Composite Semiconductor Substrates

Epitaxial structure of three semiconductor materials - silicon, gallium arsenide, and cadmium telluride - makes possible integrated monolithic focal-plane arrays of photodectors. Silicon layer contains charge-coupled devices, gallium arsenide layer contains other fast electronic circuitry, and cadmium telluride layer serves as base for array of mercury cadmium telluride infrared sensors. Technique effectively combines two well-established techniques; metalorganic chemical-vapor deposition (MOCVD) and molecular-beam epitaxy (MBE). Multilayer structure includes HgCdTe light sensors with Si readout devices and GaAs signal-processing circuits. CdTe layer provides base for building up HgCdTe layer.

Nouhi, Akbar↗
NASA NTRS1989

High-Performance Power-Semiconductor Packages

A 600-V, 50-A transistor and 1,200-V, 50-A diode in rugged, compact, lightweight packages intended for use in inverter-type power supplies having switching frequencies up to 20 kHz. Packages provide low-inductance connections, low loss, electrical isolation, and long-life hermetic seal. Low inductance achieved by making all electrical connections to each package on same plane. Also reduces high-frequency losses by reducing coupling into inherent shorted turns in packaging material around conductor axes. Stranded internal power conductors aid conduction at high frequencies, where skin effect predominates. Design of packages solves historical problem of separation of electrical interface from thermal interface of high-power semiconductor device.

Renz, David↗
NASA NTRS1988

Preparation of dilute magnetic semiconductor films by metalorganic chemical vapor deposition

A method for preparation of a dilute magnetic semiconductor (DMS) film is provided, in which a Group II metal source, a Group VI metal source and a transition metal magnetic ion source are pyrolyzed in the reactor of a metalorganic chemical vapor deposition (MOCVD) system by contact with a heated substrate. As an example, the preparation of films of Cd(sub 1-x)Mn(sub x)Te, in which 0 is less than or equal to x less than or equal to 0.7, on suitable substrates (e.g., GaAs) is described. As a source of manganese, tricarbonyl (methylcyclopentadienyl) manganese (TCPMn) is employed. To prevent TCPMn condensation during its introduction into the reactor, the gas lines, valves and reactor tubes are heated. A thin-film solar cell of n-i-p structure, in which the i-type layer comprises a DMS, is also described; the i-type layer is suitably prepared by MOCVD.

Nouhi, Akbar↗
NASA NTRS1989

High-power single spatial mode AlGaAs channeled-substrate-planar semiconductor diode lasers for spaceborne communications

A high power single spatial mode channeled substrate planar AlGaAs semiconductor diode laser was developed. The emission wavelength was optimized at 860 to 880 nm. The operating characteristics (power current, single spatial mode behavior, far field radiation patterns, and spectral behavior) and results of computer modeling studies on the performance of the laser are discussed. Reliability assessment at high output levels is included. Performance results on a new type of channeled substrate planar diode laser incorporating current blocking layers, grown by metalorganic chemical vapor deposition, to more effectively focus the operational current to the lasing region was demonstrated. The optoelectronic behavior and fabrication procedures for this new diode laser are discussed. The highlights include single spatial mode devices with up to 160 mW output at 8600 A, and quantum efficiencies of 70 percent (1 W/amp) with demonstrated operating lifetimes of 10,000 h at 50 mW.

Connolly, J. C.↗
NASA NTRS1989

Approaches toward a blue semiconductor laser

Possible approaches for obtaining semiconductor diode laser action in the blue region of the spectrum are surveyed. A discussion of diode lasers is included along with a review of the current status of visible emitters, presently limited to 670 nm. Methods are discussed for shifting laser emission toward shorter wavelengths, including the use of II-IV materials, the increase in the bandgap of III-V materials by addition of nitrogen, and changing the bandstructure from indirect to direct by incorporating interstitial atoms or by constructing superlattices. Non-pn-junction injection methods are surveyed, including avalanche breakdown, Langmuir-Blodgett diodes, heterostructures, carrier accumulation, and Berglund diodes. Prospects of inventing new multinary semiconducting materials are discussed, and a number of novel materials described in the literature are tabulated. New approaches available through the development of quantum wells and superlattices are described, including resonant tunneling and the synthesis of arbitrary bandgap materials through multiple quantum wells.

Ladany, I.↗
NASA NTRS1988

Semiconductor laser technology for remote sensing experiments

Semiconductor injection lasers are required for implementing virtually all spaceborne remote sensing systems. Their main advantages are high reliability and efficiency, and their main roles are envisioned in pumping and injection locking of solid state lasers. In some shorter range applications they may even be utilized directly as the sources.

Katz, Joseph↗
NASA NTRS1988

Transient photoconductivity in the ferromagnetic semiconductor CdCr2Se4

The transient photoconductive response time of the ferromagnetic semiconductor CdCr2Se4 was measured to be smaller than 90 ps, the response time of the scope. The measurements were performed at room temperature (300 K) for 0.53 and 1.06 microns excitations using a mode locked frequency-doubled YAG laser.

Walser, A. D.↗
NASA NTRS1989

Advantages of an indirect semiconductor quantum well system for infrared detection

The infrared intersubband absorption process in quantum well systems with anisotropic bulk effective masses, which usually occurs in indirect semiconductors was analyzed. It is found that the anisotropic effective mass can be utilized to provide allowed intersubband transitions at normal incidence to the quantum well growth direction. This transition is known to be forbidden for cases of isotropic effective mass. This property can be exploited for infrared sensor application of quantum well structures by allowing direct illumination of large surface areas without using special waveguide structures. The 10-micron intersubband absorption in quantum wells made of the silicon-based system Si/Si(1-x)Ge(x) was calculated. It is found that it is readily possible to achieve an absorption constant of the order of 10,000/cm in these Si quantum wells with current doping technology.

Yang, Chan-Lon↗
NASA NTRS1989

Total dose effect on soft error rate for dynamic metal-oxide-semiconductor memory cells

A simple model for the soft error rate for dynamic metal-oxide-semiconductor random access memories due to normal galactic radiation was devised and then used to calculate the rate of decrease of the single-event-upset rate with total radiation dose. The computation shows that the decrease in the soft error rate is less than 10 percent per day if the shielding is 0.5 g/sq cm and the spacecraft is in a geosynchronous orbit. The decrease is considerably less in a polar orbiting device.

Benumof, Reuben↗
NASA NTRS1989

Optical communication with semiconductor laser diode

This interim report describes the progress in the construction of a 220 Mbps Q=4 PPM optical communication system that uses a semiconductor laser as the optical transmitter and an avalanche photodiode (APD) as the photodetector. The transmitter electronics have been completed and contain both GaAs and ECL III IC's. The circuit was able to operate at a source binary data rate from 75 Mbps to 290 Mbps with pulse rise and fall times of 400 ps. The pulse shapes of the laser diode and the response from the APD/preamplifier module were also measured.

Davidson, Frederic↗
NASA NTRS1989

Electron-beam induced damage in thin insulating films on compound semiconductors

Phosphorus rich plasma enhanced chemical vapor deposition (PECVD) of silicon nitride and silicon dioxide films on n-type indium phosphide (InP) substrates were exposed to electron-beam irradiation in the 5 to 40 keV range for the purpose of characterizing the damage induced in the dielectric. The electron-beam exposure was on the range of 10(exp -7) to 10(exp -3) C/sq cm. The damage to the devices was characterized by capacitance-voltage (C-V) measurements of the metal insulator semiconductor (MIS) capacitors. These results were compared to results obtained for radiation damage of thermal silicon dioxide on silicon (Si) MOS capacitors with similar exposures. The radiation induced damage in the PECVD silicon nitride films on InP was successfully annealed out in an hydrogen/nitrogen (H2/N2) ambient at 400 C for 15 min. The PECVD silicon dioxide films on InP had the least radiation damage, while the thermal silicon dioxide films on Si had the most radiation damage.

Pantic, Dragan M.↗
NASA NTRS1990

Photoreflectance for in-situ characterization of MOCVD growth of semiconductors under micro-gravity conditions

A contactless electromodulation technique of photoreflectance (PR) was developed for in-situ monitoring of metal-organic chemical vapor deposition (MOCVD) semiconductor growth for micro-gravity applications. PR can be employed in a real MOCVD reactor including rotating substrate (approximately 500 rev/min) in flowing gases and through a diffuser plate. Measurements on GaAs and Ga(0.82)Al(0.18)As were made up to 690 C. The direct band gaps of In(x)Ga(1-x)As (x = 0.07 and 0.16) were evaluated up to 600 C. In order to address the question of real time measurement, the spectra of the direct gap of GaAs at 650 C was obtained in 30 seconds and 15 seconds seems feasible.

Pollak, Fred H.↗
NASA NTRS1989

Influence of non steady gravity on natural convection during micro-gravity solidification of semiconductors. I - Time scale analysis. II - Implications for crystal growth experiments

Consideration is given to the influence of temporal variations in the magnitude of gravity on natural convection during unidirectional solidification of semiconductors. It is shown that the response time to step changes in g at low Rayleigh numbers is controlled by the momentum diffusive time scale. At higher Rayleigh numbers, the response time to increases in g is reduced because of inertial effects. The degree of perturbation of flow fields by transients in the gravitational acceleration on the Space Shuttle and the Space Station is determined. The analysis is used to derive the requirements for crystal growth experiments conducted on low duration low-g vehicles. Also, the effectiveness of sounding rockets and KC-135 aircraft for microgravity experiments is examined.

Griffin, P. R.↗
NASA NTRS1990

Semiconductor surface sublimation energies and atom-atom interactions

The energy required to remove an atom from semiconductor surfaces is calculated using a Green's-function approach. Contrary to intuition, it is found that, in some cases, less energy is needed to remove an atom from the nearly full surface than from a nearly empty surface. The results are explained in terms of the relative energies of anion and cation dangling bonds, and the charge transfers between them. The deducted effective pair-interaction energies and their effects on surface morphology and growth perfection are discussed.

Krishnamurthy, Srinivasan↗