High Quality, Low Cost Ammonothermal Bulk GaN Substrates

Ammonothermal GaN growth using a novel apparatus has been performed on c-plane, m-plane, and semipolar seed crystals with diameters between 5 mm and 2 in. to thicknesses of 0.5–3 mm. The highest growth rates are greater than 40 µm/h and rates in the 10–30 µm/h range are routinely observed for all orientations. These values are 5–100× larger than those achieved by conventional ammonothermal GaN growth. The crystals have been characterized by X-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), optical spectroscopy, and capacitance–voltage measurements. The crystallinity of the grown crystals is similar to or better than that of the seed crystals, with FWHM values of about 20–100 arcsec and dislocation densities of 1 ×105–5 ×106 cm-2. Dislocation densities below 104 cm-2 are observed in laterally-grown crystals. Epitaxial InGaN quantum well structures have been successfully grown on ammonothermal wafers.