Engineering topics

Yamakawa, K. A.

Publications and source records attributed to Yamakawa, K. A..

13 records

NASA NTRS1986

Increasing the Deposition Rate of Silicon

Modified Siemens reactor enables chemical vapor deposition (CVD) of silicon to occur simultaneously on inner and outer surfaces of hollow cylinder, resulting in increase in mass of silicon deposited per unit time. Outer reactor for silicon deposition made from quartz or stainless steel. Hollow cylinder either single resistance-heated hollow cylinder about 5 to 10 cm or greater in diameter or 1-cm-diameter rods aligned in circular channels at top and bottom, initial circles being 5 to 10 cm in diameter or greater.

Lutwack, R.↗

NASA NTRS1985

Cleaning The Walls of A Silane Reactor

Scraper removes silicon deposits from inner walls of reactor vessel. Scraper supported by gas bearing. Scraper made of non-contaminating material such as quartz or silicon.

Yamakawa, K. A.↗

NASA NTRS1985

Apparatus and method to keep the walls of a free-space reactor free from deposits of solid materials

An apparatus and method is disclosed for keeping interior walls of a reaction vessel free of undesirable deposits of solid materials in gas-to-solid reactions. The apparatus includes a movable cleaning head which is configured to be substantially complementary to the interior contour of the walls of the reaction vessel. The head ejects a stream of gas with a relatively high velocity into a narrow space between the head and the walls. The head is moved substantially continuously to at least intermittently blow the stream of gas to substantially the entire surface of the walls wherein undesirable solid deposition is likely to occur. The disclosed apparatus and process is particularly useful for keeping the walls of a free-space silane-gas-to-solid-silicon reactor free of undesirable silicon deposits.

Yamakawa, K. A.↗

NASA NTRS1984

Sampling of Silicon Powder for Impurity Analysis

Electron beam forms dense pellets of powdered silicon for Zeeman analysis. Sampling method focuses electron beam on submicron silicon powder. Process enhances quality control in production of low-cost silicon powder for semiconductor industry.

Yamakawa, K. A.↗

NASA NTRS1983

Solar-Cell Slide Rule

Slide rule relates efficiency, impurity types, impurity concentrations, and process types. Solar cell slide rule calculations are determination of allowable impurity concentration for nonredistributive process, determination of impurity buildup factor for redistributive process and determination of allowable impurity concentration for redistributive process.

Yamakawa, K. A.↗

NASA NTRS1983

Consolidating Submicron Silicon Particles

Molten-silicon pool receives fine silicon powder and melts it. After stable molten layer forms, pedestal is lowered at rate equal to siliconpowder feed rate. If silane is directly decomposed on silicon pool, powder feeder is replaced by jet of silane on silicon surface, and hydrogen produced in decomposition of solane is pumped from bottom end of chamber.

Yamakawa, K. A.↗

NASA NTRS1982

Reduction of solar cell efficiency by edge defects across the back-surface-field junction - A developed perimeter model

Material imperfections, impurity clusters and fabrication defects across the back-surface-field junction can degrade the performance of high-efficiency solar cells. The degradation from defects appearing on the circumference of a solar cell is analyzed using a two-region developed perimeter device model. The width of the defective perimeter region is characterized by the range or the distance-of-influence of the defective edge and this width is about two diffusion lengths. The defective edge is characterized by a surface recombination velocity. Family of theoretical curves and numerical examples are presented to show that significant reduction of open-circuit voltage can occur in high-efficiency cells which are thin compared with the diffusion length. In one example, the degradation is decreased from 135 mV to 75 mV when the cell size is increased from 10 to 100 times the diffusion length in a thin cell whose thickness is 1% of the diffusion length.

Sah, C. T.↗

NASA NTRS1982

Effect of thickness on silicon solar cell efficiency

A computer-aided-design study on the dependence of the efficiency peak of a back-surface field solar cell on the concentrations of the recombination and dopant impurities is presented. The illuminated current-voltage characteristics of more than 100 cell designs are obtained using the transmission line circuit model to numerically solve the Shockley equations. Using an AM 1 efficiency of 17% as a target value, it is shown that the efficiency versus thickness dependence has a broad maximum which varies by less than 1% over more than a three-to-one range of cell thicknesses from 30 to 100 microns. An optically reflecting back surface will give only a slight improvement of AM 1 efficiency, about 0.7%, in this thickness range. Attention is given to the dependence of the efficiency on patchiness across the back-surface field low-high junction in thin cells.

Sah, C.-T.↗

NASA NTRS1982

Reduction of solar cell efficiency by bulk defects across the back-surface-field junction

The degradation of solar cell performance due to bulk defects distributed across the back-surface field junction is analyzed in terms of a three-region developed-perimeter model. Families of curves are computed and their physical significance is discussed in detail with reference to three parameters used to characterize the defects: defect area, defect density, and defect surface recombination velocity. A reduction in the open-circuit voltage due to the presence of a defect is expressed as a function of the defect area, density, cell thickness, and defect surface recombination velocity. Numerical examples are presented to illustrate the importance of the particular defect parameters.

Sah, C. T.↗

NASA NTRS1981

Scriber for silicon wafers

A device for dividing silicon wafers into rectangular chips is characterized by a base including a horizontally oriented bed with a planar support surface, a vacuum chuck adapted to capture a silicon wafer seated on the support for translation in mutually perpendicular directions. A stylus support mounted on the bed includes a shaft disposed above and extended across the bed and a truck mounted on the shaft and supported thereby for linear translation along a path extended across the bed a vertically oriented scribe has a diamond tip supported by the truck also adapted as to engage a silicon wafer captured by the chuck and positioned beneath it in order to form score lines in the surface of the wafer as linear translation is imparted to the truck. A chuck positioning means is mounted on the base and is connected to the chuck for positioning the chuck relative to the stylus.

Yamakawa, K. A.↗

NASA NTRS1981

The effects of impurities on the performance of silicon solar cells

The major factors that determine the tolerable concentrations of impurities in silicon feedstock for solar cells used in power generation are discussed in this report. It is concluded that a solar-grade silicon can be defined only for a specific manufacturing process. It is also concluded that it is the electrical effects, efficiency and resistivity, that are dominant in determining tolerable concentrations of impurities in the silicon feedstock. Crystal growth effects may become important when faster growth rates and larger crystal diameters are developed and used.

Yamakawa, K. A.↗

NASA NTRS1981

Effect of zinc impurity on silicon solar-cell efficiency

Zinc is a major residue impurity in the preparation of solar-grade silicon material by the zinc vapor reduction of silicon tetrachloride. This paper projects that in order to get a 17-percent AM1 cell efficiency for the Block IV module of the Low-Cost Solar Array Project, the concentration of the zinc recombination centers in the base region of silicon solar cells must be less than 4 x 10 to the 11th Zn/cu cm in the p-base n+/p/p+ cell and 7 x 10 to the 11th Zn/cu cm in the n-base p+/n/n+ cell for a base dopant impurity concentration of 5 x 10 to the 14 atoms/cu cm. If the base dopant impurity concentration is increased by a factor of 10 to 5 x 10 to the 15th atoms/cu cm, then the maximum allowable zinc concentration is increased by a factor of about two for a 17-percent AM1 efficiency. The thermal equilibrium electron and hole recombination and generation rates at the double-acceptor zinc centers are obtained from previous high-field measurements as well as new measurements at zero field described in this paper. These rates are used in the exact dc-circuit model to compute the projections.

Sah, C.-T.↗

NASA NTRS1972

Radiation effects on three low-power microcircuits

Irradiation of several low power circuit elements by Co-60 gamma radiation, low and high energy electrons, and neutrons is discussed. The bipolar circuits were SE480 Q NAND gate, and a micropower frequency divider was used in electronic wrist watches. The MOS device was a dual p-channel MOSFET.

Yamakawa, K. A.↗