Transparent, conductive bulk GaN by high temperature ammonothermal growth

A novel, highly scalable apparatus has been employed to perform high temperature ammonothermal growth of (0001) GaN bulk crystals up to 52 mm in diameter and to a thickness of greater than 2 mm. X-ray characterization of the crystals shows excellent crystallinity with radii of curvature > 20 m and a 201 rocking curve FWHM of <30 arcsec. Hall effect and optical absorption measurements performed on the crystal show a free carrier concentration of 1.1 × 1018 cm−3 and an absorption coefficient of 1 cm−1 at 450 nm and 2 cm−1 at 410 nm, meeting the substrate requirements for use as a native substrate in blue or violet LED devices. To the best of our knowledge, this is the lowest optical absorption coefficient reported for ammonothermally-grown GaN having a carrier concentration above 1018 cm−3.