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Start Over Author "Freitas, J" Journal applied physics letters
20 results on '"Freitas, J"'

18. On-demand atmospheric pressure storage system for AsH3 and PH3.

Author

Sillmon, R. S. and Freitas, J. A.

Subjects
*ATMOSPHERIC pressure, *COMPRESSED gas, *GAS absorption & adsorption
Abstract

An on-demand atmospheric pressure storage system for AsH3 and PH3, which eliminates the sudden release hazard associated with compressed gases, has been developed and tested with AsH3. The storage system is based on the adsorption of these gases into the microcavities of synthetic zeolites at 23 °C and subsequent desorption at higher temperatures. The adsorption isotherm and isobar of AsH3 on NaA and CaA zeolites were measured. At 23 °C and 760 Torr AsH3 pressure, an adsorption capacity of 25 wt. % (AsH3/zeolite) was measured for CaA zeolite. About 100% of the adsorbed AsH3 was recovered at desorption temperatures below 190 °C. Preliminary results of operating a 500 cc prototype AsH3-zeolite storage system connected to an organometallic vapor phase epitaxy reactor for the growth of GaAs and AlGaAs show that the purity of the AsH3 is retained during the adsorption/desorption process. [ABSTRACT FROM AUTHOR]

Published
1990
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19. New deep acceptor in epitaxial cubic SiC.

Author

Freitas, J. A. and Bishop, S. G.

Subjects
*PHOTOLUMINESCENCE, *THIN films, *SILICON carbide, *CHEMICAL vapor deposition, *SILICON
Abstract

We have investigated the temperature and excitation intensity dependence of photoluminescence (PL) spectra in several undoped and lightly Al-doped thin films of cubic SiC grown by chemical vapor deposition on Si substrates. The low-power PL spectra in all samples studied exhibit a deep donor-acceptor pair PL band which involves a previously undetected deep acceptor (EA=470 meV). The pervasive character of this deep acceptor suggests the possibility that it is at least partially responsible for the high compensation observed in undoped films of cubic SiC. [ABSTRACT FROM AUTHOR]

Published
1989
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20. Donor binding energies determined from temperature dependence of photoluminescence spectra in undoped and aluminum-doped beta SiC films.

Author

Freitas, J. A., Bishop, S. G., Nordquist, P. E. R., and Gipe, M. L.

Subjects
*BINDING energy, *SILICON carbide, *PHOTOLUMINESCENCE
Abstract

Measurements of the temperature dependence of N-Al donor-acceptor pair photoluminescence spectra in cubic SiC films demonstrate that the thermal activation energy for the nitrogen donors is equivalent to the 54 meV binding energy for nitrogen determined from the spectral energies of the sharp-line close pair spectra. It follows that the 15–20 meV donor which dominates the electrical properties of n-type films is not isolated, substitutional nitrogen. Spatial variations observed in the intensity of a new 2.368 eV luminescence band demonstrate that the radiative recombination centers are inhomogeneously distributed in the films. [ABSTRACT FROM AUTHOR]

Published
1988
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