According to the ’268 patent, silicon carbide is an attractive material to use as a substrate for the growth of bulk Group III nitrides (such as gallium nitride), since it can be conductively doped and has various desirable properties, such as a wide bandgap, a high melting point, a high thermal conductivity, and a high breakdown electric field. When silicon carbide is used as a growth substrate for Group III nitrides, the mismatch between the lattice constants of the two materials can be ameliorated using one or more intermediate “buffer” layers between the two to minimize the number of unwanted defects in the grown layer. The ’268 patent discloses a particular structure for such a buffer layer comprising a thin, discontinuous layer of AlGaN on the substrate and a relatively thick layer of GaN on the discontinuous AlGaN layer.
According to its website, Cree is “leading the LED lighting revolution … through the use of energy-efficient, environmentally friendly LED lighting.” I first heard about Cree, based in Durham, NC, back in 1997 when I was a post-doc researcher in the Chemistry Dept. of the Univ. of North Carolina, Chapel Hill. At that time, the company was creating a significant buzz with its advances in growing high-quality silicon carbide wafers and developing high-power microwave transistors and blue LEDs. Now the company’s product line extends to high-brightness LEDs for general illumination, and has grown to have $867 million in revenues in 2010. Cree has an interesting blog that publicizes its efforts in the “LED lighting revolution.”
According to the USPTO database, Cree received 103 U.S. patents in 2010, compared to 70 in 2009 and 71 in 2008.