Highly transparent ammonothermal bulk GaN substrates

A novel apparatus has been employed to grow ammonothermal (0001) gallium nitride (GaN) with diameters up to 2 in. The crystals have been characterized by x-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), and optical spectroscopy. High crystallinity GaN with FWHM values about 20-50 arcsec and dislocation densities below 1×105 cm−2 have been obtained. High optical transmission was achieved with an optical absorption coefficient below 1 cm−1 at a wavelength of 450 nm.