Basic ammonothermal growth of GaN crystals was studied. We examined the effect of different sodium-based mineralizers, including sodium amide, sodium azide, and sodium metal, on the growth rate and quality of the as-grown GaN crystals. Ammonothermally grown GaN crystal in sodium metal mineralizer showed significant increase in both the growth rate and quality of the as-grown GaN crystals. The full-width half-maximum values of the as-grown GaN crystal using sodium metal mineralizer were 270 arc-sec for Ga face and 88 arcsec for N face. Also, we reported approximately 2 in. GaN crystals using sodium metal mineralizer. Ammonothermally grown GaN crystal showed higher chemical stability than HVPE-grown GaN crystal after H3PO4 etching at 160 degrees C for 2 h. The dark spot density in cathodoluminescence image was measured at the level of 1 x 10(5)/cm(2). (C) 2017 Elsevier B.V. All rights reserved.