Abstract: Large area seed crystals for ammonothermal GaN growth are fabricated by deposition or layer transfer of a GaN layer on a CTE-matched handle substrate. The sides and back of the handle substrate are protected from the ammonothermal growth environment by a coating comprising an adhesion layer, a diffusion barrier layer, and an inert layer. A patterned mask, also comprising an adhesion layer, a diffusion barrier layer, and an inert layer, may be provided over the GaN layer to allow for reduction of the dislocation density by lateral epitaxial growth.

Abstract: A high pressure apparatus and related methods for processing supercritical fluids are disclosed. In certain embodiments, the present apparatus includes a capsule, a heater, at least one ceramic ring or multiple rings, optionally, with one or more scribe marks and/or cracks present. In certain embodiments, the apparatus has a metal sleeve containing each ceramic ring. The apparatus also has a high strength enclosure, end flanges with associated insulation, and a power control system. In certain embodiments, a high pressure apparatus is constructed such that the diametric annular gap between the outer diameter of the heater and the ceramic ring is selected to provide radial load-bearing contact above a particular temperature and pressure. In certain embodiments, the apparatus is capable of accessing pressures of 0.2 GPa to 2 GPa and temperatures of 400° C. to 1200° C.