High-temperature gallium nitride (GaN) crystal growth using the acidic ammonothermal method with ammonium iodide (NH4I) as a mineralizer was investigated. The growth rate reached 105 mu m/day, which was much higher than that previously achieved using acidic ammonothermal methods, and exceeded 100 mu m/day, which is the minimum growth rate required for industrial applications. When NH4I was used as a mineralizer, high-speed crystal growth was achieved at a relatively low pressure compared to the case of using an ammonium chloride (NH4Cl) as a mineralizer. (C) 2012 Elsevier B.V. All rights reserved.