Tohoku University, Japan Steel Works Corporation, and Mitsubishi Chemical Corporation have developed a low-pressure acid ammonia heating (LPAAT) method that can mass produce gallium nitride single crystal substrates with a diameter of more than 2 inches. By realizing low-pressure crystal growth, large crystals can be mass-produced in a relatively small crystal growth furnace. A 2-inch long gallium nitride single crystal substrate fabricated on the gallium nitride seed crystal based on the SCAAT method using the LPAAT method has a low crystal mosaic (the half-value width of the X-ray rocking curve of the symmetric and asymmetric surfaces is within 28 seconds ), the substrate has almost no good crystal structure characteristics of warpage (the radius of curvature is about 1.5 km).
If large-diameter, low-warpage, high-purity GaN single crystal substrates made by the LPAAT method are popularized, GaN vertical power transistors with excellent reliability are expected to be practical.