LiAlO2 is not a big secret, it seems.
From Bell Labs [Lucent] in 1997:
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Epitaxial Growth and Orientation of GaN on (1 0 0) -LiAlO2
E. S. Hellman
Bell Laboratories, Lucent Technologies
Z. Liliental-Weber
Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley CA 94720
D. N. E. Buchanan
Bell Laboratories, Lucent Technologies
This article was received on Friday, June 20, 1997 and accepted on Monday, September 15, 1997.
Abstract
The (1 0 0) face of -LiAlO2 has attracted attention as a possible substrate for GaN epitaxial growth. This is partly because this face has an excellent lattice and structural match to (1 0 0) GaN. This orientation would have a misfit of only -1.4% along the c-direction and -0.1% along the b-direction of LiAlO2. We find that in practice this orientation relationship does not occur; instead, (0 0 0 1) oriented GaN grows with a small tilt (0.6° towards the c-direction) between the film and substrate. Although the misfit along the substrate b direction is large (-6.3%) for this orientation, the tilt perfectly accommodates the -1.4% misfit in the c direction. We present characterization of these films by RHEED, X-ray diffraction, and TEM. We propose that the tilt is driven by a reduction of interface energy which occurs in polar, incoherent interfaces.
Outline
Introduction
Epitaxial Growth
Film Characterization
Transmission Electron Microscopy
X-ray diffraction
SIMS
Electrical
Discussion
Conclusion
Acknowledgments
(all good things come from Bell Labs ultimately)
LiAlO2 is not a big secret, it seems. I agree that the big (i.e., money-making) boys would have picked up on it if it had obvious economic potential....who's to say it ultimately doesn't, though... Crystal Photonics was the source of Lucent's wafers as well...
Intersting summary from a GaN workwhop in England last month: multilayer GaN/InGaN quantum dot structures grown on Si substrates could theoretically emit white light:
Several groups reported a related development on QD structures for LEDs. Interestingly such structures may be grown on silicon, despite a very high dislocation density, since with an optimized dot size and density (of the order 1011 cm-2) most dots will not encounter any dislocations. Efficient LEDs based on such InGaN/GaN QD structures covering the entire range from blue to red were demonstrated. It was claimed that the controlled deposition of two different sizes of QDs in a multilayer structure grown on silicon would be an attractive concept for white LEDs.
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