Ammonothermal crystal growth of GaN using an NH₄F mineralizer

NH₄F is demonstrated to be a promising mineralizer for the acidic ammonothermal crystal growth of GaN. In comparison with other acidic mineralizers such as NH₄Cl, NH₄Br, and NH₄I, NH₄F behaves distinctively different. First, NH₄F affords a negative temperature gradient for crystal growth of GaN in supercritical NH₃ at a temperature range from 550 to 650 C. Second, it enables GaN crystal growth in polar (c plane), semipolar, and nonpolar directions (a plane and m plane). Third, NH₄F remarkably increases both the growth rate and quality of the GaN crystal. With the aid of NH₄F, self-nucleation of GaN and bulk growth of hexagonal GaN crystals from the self-nucleated seed have been realized.