NASA Scientific and Technical Aerospace Reports

20040068232 Lockheed Martin Corp., Syracuse, NY, USA
Self-Organized Superlattices in GaInAsSb Grown on Vicinal Substrates
Wang, C. A.; Vineis, C. J.; Calawa, D. R.; Jun. 2003; 18 pp.; In English
Report No.(s): DE2004-822275; LM-03K116; No Copyright; Avail: Department of Energy Information Bridge
Self-organized superlattices are observed in GaInAsSb epilayers grown lattice matched to vicinal GaSb substrates. The
natural superlattice (NSL) is oriented at a slight angle of about 4(sup o) with respect to the vicinal (001) GaSb substrate. This
vertical composition modulation is detected at the onset of growth. Layers in the NSL are continuous over the lateral extent
of the substrate. Furthermore, the NSL persists throughout several microns of deposition. The NSLs have a period ranging
from 10 to 30 nm, which is dependent on deposition temperature and GaInAsSb alloy composition. While the principle driving
force for this type of phase separation is chemical, the mechanism for the self-organized microstructure is related to local
strains associated with surface undulations. By using a substrate with surface undulations, the tilted NSL can be induced in
layers with alloy compositions that normally do not exhibit this self-organized microstructure under typical growth conditions.
These results underscore the complex interactions between compositional and morphological perturbations.
NTIS
Superlattices; Gallium Arsenides; Gallium Antimonides; Alloys
20040068239 Lockheed Martin Corp., Syracuse, NY, USA
GaAs Films Prepared by RF-Magnetron Sputtering
Ouyang, L. H.; Rode, D. L.; Zulkifli, T.; Abraham-Shrauner, B.; Lewis, N.; Aug. 2001; 32 pp.; In English
Report No.(s): DE2004-821684; LM-01K067; No Copyright; Avail: Department of Energy Information Bridge
The authors reported on the optical absorption, adhesion, and microstructure of RF-magnetron sputtered films of
hydrogenated amorphous and microcrystalline GaAs films for the 1 to 25(micro)m infrared wavelength rate. Sputtering
parameters which were varied include sputtering power, temperature and pressure, and hydrogen sputtering-gas concentration.
TEM results show a sharp transition from purely amorphous GaAs to a mixture of microcrystalline GaAs in an amorphous
matrix at 34(+-) 2 C. By optimizing the sputtering parameters, the optical absorption coefficient can be decreased below 100
cm(sup -1) for wavelengths greater than about 1.25(micro)m. These results represent the lowest reported values of optical
absorption for sputtered films of GaAs directly measured by spectrophotometry for the near-infrared wavelength region.
NTIS
Gallium Arsenides; Sputtering
20040068255 Lockheed Martin Corp., Syracuse, NY, USA
Reduction of Micro-Cracks in Large Diameter InxGa1-xSb Bulk Crystals
Vogel, J.; Dutta, P. S.; Apr. 2003; 12 pp.; In English
Report No.(s): DE2004-821510; LM-03K034; No Copyright; Avail: Department of Energy Information Bridge
The ternary alloy, In(sub x)Ga(sub 1-x)Sb, is a compound semiconductor of tunable bandgap in the range of 0.18-0.72
eV, making it useful for infrared range optoelectronic devices. Utilizing a unique system based upon vertical Bridgman
technique, large diameter (50 millimeter) In(sub x)Ga(sub 1-x)Sb polycrystals of composition ranging in x from 0.015 to 0.988
were grown. Methods of mixing the melt during solidification, including the accelerated crucible rotation technique (ACRT),
have been used in conjunction with optimization of the furnace temperature gradient profile to significantly reduce
micro-cracking in the crystal boules while accelerating the growth rate from less than a millimeter per hour to three millimeters
per hour. In this paper, the experimental system and crystal growth parameters for a set of ternary experiments will be detailed.
NTIS
Alloys; Crystal Growth
20040068266 Lawrence Livermore National Lab., Livermore, CA
Estimates of Imaging Times for Conventional and Synchrotron X-Ray Sources
Kinney, J.; May 20, 2003; In English
Report No.(s): DE2003-15004930; UCRL-ID-153337; No Copyright; Avail: National Technical Information Service (NTIS)
The following notes are to be taken as estimates of the time requirements for imaging NIF targets in three-dimensions
with absorption contrast. The estimates ignore target geometry and detector inefficiency, and focus only on the statistical
question of detecting compositional (structural) differences between adjacent volume elements in the presence of noise. The
basic equations, from the classic reference by Grodzins, consider imaging times in terms of the required number of photons
necessary to provide an image with given resolution and noise. The time estimates, therefore, have been based on the
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