Ammonothermal recrystallization of gallium nitride with acidic mineralizers

Crystals of cubic GaN (c-GaN) were grown ammonothermally using hexagonal gallium nitride as a nutrient. h-GaN was sealed in a quartz tube with anhydrous ammonia, an acid (NH4X; X = Cl, Br, I), and in some cases a lithium halide (LiX). The bottom of the tube was heated to 470-510 degreesC in a vertically oriented pressure vessel containing a hydrostatic pressure of 30000-40000 psi. The thermal gradient was approximately -10 degreesC/cm. h-GaN dissolved in the hot zone and GaN crystals deposited in the cooler zone near the top of the tube. Most (> 80%) of the deposit was c-GaN for most of the experimental conditions studied, but the hexagonal form was a persistent contaminant. When LiX was used as a co-mineralizer triangular prisms of c-GaN often grew. Triangular prismatic needles of c-GaN grew in a (1 (1) over bar1) direction in experiments containing a low concentration (0.28 mol %) of NH4Cl, a larger concentration (2.0 mol %) of LiCl, and a 55% fill factor. The crystals were tapered, becoming wider as they grew, and crystals of up to 0.1 mm in width were obtained.