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.