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Your search keyword '"Branz, Howard M."' showing total 396 results
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396 results on '"Branz, Howard M."'

1. Understanding the Clean Interface between Covalent Si and Ionic Al2O3

Author

Xiang, H. J., Da Silva, Juarez L. F., Branz, Howard M., and Wei, Su-Huai

Subjects
Condensed Matter - Materials Science
Abstract

The atomic and electronic structures of the (001)-Si/(001)-gamma-Al2O3 heterointerface are investigated by first principles total energy calculations combined with a newly developed "modified basin-hopping" method. It is found that all interface Si atoms are fourfold coordinated due to the formation of Si-O and unexpected covalent Si-Al bonds in the new abrupt interface model. And the interface has perfect electronic properties in that the unpassivated interface has a large LDA band gap and no gap levels. These results show that it is possible to have clean semiconductor-oxide interfaces.

Published
2009
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10. Substitutional n-type doping of an organic semiconductor investigated by electron paramagnetic resonance spectroscopy

Author

Si-Guang Chen, Branz, Howard M., Eaton, Sandra S., Cormier, Russel A., and Gregg, Brian A.

Subjects
Organic semiconductors -- Electric properties, Electron paramagnetic resonance -- Usage, Chemicals, plastics and rubber industries
Abstract

Electron paramagnetic resonance (EPR) and optical spectroscopy were used to characterize the doping process in a liquid crystal perylene dimide, PPEB. Studies of the dopant solutions indicated that a small fraction of the dopant was reversibly quenched by an unknown impurity.

Published
2004

47. Physics and chemistry of hot-wire chemical vapor deposition from silane: Measuring and modeling the silicon epitaxy deposition rate.

Author

Martin, Ina T., Teplin, Charles W., Doyle, James R., Branz, Howard M., and Stradins, Paul

Subjects
CHEMICAL vapor deposition, SILANE, PHOTOVOLTAIC cells, EPITAXY, PHYSICS experiments
Abstract

We measure and successfully model the deposition rate (R) of epitaxial Si by hot-wire chemical vapor deposition (HWCVD) onto (100) silicon over a wide range of growth conditions. A deposition rate model based on the fundamentals of gas-filament and gas-substrate interactions is presented; the results are consistent with the observed dependences of R on gas pressure, flow, and filament area. Gas-phase measurements of silane depletion allow calculation of the average radical sticking coefficient from the film deposition rate. Our findings indicate that the epitaxial deposition rate can be increased sufficiently to enable an economical epitaxial film-silicon photovoltaic tech-nology on low-cost foreign substrates. The model can be simply adapted to apply to the HWCVD of amorphous, nanocrystalline, and polycrystalline Si. [ABSTRACT FROM AUTHOR]

Published
2010
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48. Electron transport and band structure in phosphorus-doped polycrystalline silicon films.

Author

Young, David L., Branz, Howard M., Liu, Fude, Reedy, Robert, To, Bobby, and Wang, Qi

Subjects
*FREE electron theory of metals, *PARTICLES (Nuclear physics), *CRYSTALLIZATION, *ELECTRIC conductivity, *PHYSICAL & theoretical chemistry, *SEPARATION (Technology), *SILICON
Abstract

We study transport mechanisms, effective mass, and band structure by measuring the resistivity, Hall, and Seebeck and Nernst coefficients in heavily phosphorus-doped polycrystalline silicon films made by thermal crystallization of amorphous silicon. We observe a change in transport mechanism which results in an increase in electron mobility from 10% to 80% of the single-crystal silicon mobility as the carrier concentration increases from 1019 to 1020 cm-3. Our measurements of effective mass at the Fermi level indicate that as the carrier concentration increases, there is a shift from impurity-band transport to conduction-band transport, and that the electron effective mass is lower in the impurity band than in the conduction band of Si. The shift to conduction-band transport improves electron mobility with carrier density by improving intragrain carrier mean free path lengths and relaxation times. [ABSTRACT FROM AUTHOR]

Published
2009
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49. Exciton harvesting, charge transfer, and charge-carrier transport in amorphous-silicon nanopillar/polymer hybrid solar cells.

Author

Gowrishankar, Vignesh, Scully, Shawn R., Chan, Albert T., McGehee, Michael D., Qi Wang, and Branz, Howard M.

Subjects
NANOSTRUCTURES, SILICON, AMORPHOUS substances, SOLAR cells, DIFFUSION, PHYSICS
Abstract

We report on the device physics of nanostructured amorphous-silicon (a-Si:H)/polymer hybrid solar cells. Using two different polymers, poly(3-hexylthiophene) (P3HT) and poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV), we study the exciton diffusion, charge transfer, and charge-carrier transport in bilayer and nanostructured a-Si:H/polymer systems. We find that strong energy transfer occurs in the a-Si:H/MEH-PPV system. However, inefficient hole transfer from the a-Si:H to the polymers renders negligible photocurrent contribution from the a-Si:H as well as very small currents in the a-Si:H/MEH-PPV devices. These results suggest that a-Si:H may be unsuitable for use in polymer-based hybrid cells. Nanosphere lithography and reactive ion etching were used to fabricate nanopillars in a-Si:H. The nanostructured a-Si:H/P3HT devices showed improved efficiency and almost perfect charge-carrier extraction under short-circuit conditions. By modeling these nanostructured devices, the loss mechanisms were identified and solutions for higher efficiencies are suggested. [ABSTRACT FROM AUTHOR]

Published
2008
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50. Significant improvement in silicon chemical vapor deposition epitaxy above the surface dehydrogenation temperature.

Author

Wang, Qi, Teplin, Charles W., Stradins, Paul, To, Bobby, Jones, Kim M., and Branz, Howard M.

Subjects
SILICON, CHEMICAL vapor deposition, EPITAXY, DEHYDROGENATION, TRANSMISSION electron microscopy
Abstract

We observe an order of magnitude increase in both the rate and achievable thickness of epitaxy by hot-wire chemical vapor deposition at temperatures above the dehydrogenation temperature of the silicon surface. We deposit silicon films on (100) silicon at 110 nm/min at substrate temperatures between 520 and 645 °C. At the glass compatible temperature of 610 °C, we observe phase-pure epitaxial growth of more than 10 μm, as observed by x-ray diffraction and transmission electron microscopy, in contrast to the mixed-phase breakdown seen at lower temperatures. In 610 °C films thicker than 4 μm, a stable (100)-epitaxial growth mode produces regular surface pyramids with vicinal <311> facets. On the low-energy (111) face of Si, more than 2 μm of epitaxial Si were grown at 645 °C, but some twinning is observed. The temperature of this new growth regime suggests that rapid dehydrogenation of the growing surface is critical for silicon epitaxy by CVD. [ABSTRACT FROM AUTHOR]

Published
2006
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