Fabrication of cubic gallium nitride single crystal using a K-Ga melt

Granular and platelet-shaped gallium nitride (GaN) crystals were prepared at 600-700°C and 4-7 MPa of N₂ for 24-96 h by using a K-Ga melt. The granular crystals with a size of 50-80 μm were a mixture of cubic zincblende-type GaN (c-GaN) and hexagonal wurztite-type GaN (h-GaN). The ratio of c-GaN in the mixture increased with decreasing temperature and with decreasing N₂ pressure. The platelet crystals obtained were h-GaN and have a size of about 1 mm. A colorless transparent grain of GaN with a size of 80 μm was characterized by cathodoluminescence (CL) spectroscopy at room temperature. A CL peak with a full width at half maximum of 76 meV was observed at 3.209 eV which agreed with the near band emission peak position reported for c-GaN thin films.