Research Review: Ammonothermal yields high-quality semi-polar GaN
Working in partnership with Wroclaw University of Technology, Poland, Ammono has employed X-ray diffraction to probe its semi-polar material that is produced in a high-pressure ammonia solution. X-ray diffraction rocking curves on pieces of (2021) GaN, which has a typical dislocation density of 5 x 103 cm-2 and a radius of curvature in excess of 100 m, produce a full width at half maximum of just 17 and 21 arcsec for the (2021) and (2020) peaks. “The best crystallographic properties and the lowest dislocation density may suggest the best semi-polar GaN ever produced,” says Ammono president Robert Dwilinski.
Contactless electroreflectance has also been used to study semi-polar (2021) GaN. “With this technique, instead of measuring the optical reflectance of the material, the derivative with respect to a modulating electric field is evaluated,” explains Dwilinski. This measurement yielded a sharp, strong resonance peak at 3.4 eV, indicating that the sample had both good optical properties and a good surface.
The piece of semi-polar GaN studied by the Polish researchers had dimensions of 9 mm by 12 mm. But far larger sizes should be possible, given that Ammono has already produced 1-inch GaN non-polar crystals that can yield semi-polar substrates of at least that size. Today the Polish company sells 10 mm x 10 mm, 10 mm x 20 mm and 13 mm x 15 mm substrates. “We will work to increasing the size of our semi polar substrates to 1-inch in 2011,” says Dwilinski.
“This size is not available on the commercial market, and is hardly achievable by HVPE.” R. Kucharski et al. Appl. Phys Express 3 101001 (2010)
Ammono is pioneering ammonothermal
growth of semi-polar and polar GaN
