Effect of flux composition ratio on the coalescence growth of GaN crystals by the Na-flux method

Previously, we demonstrated that the Na-flux coalescence growth technique had high potential for the fabrication of large-diameter, high-quality GaN crystals. This present study investigates the relation between the flux composition (Ga/Na) and void formation in GaN crystals grown by this technique. It was found that void formation decreases with a decrease in the Ga composition of the flux and that stable coalescence with no voids at the GaN grain boundaries occurred for a Ga composition of 15 mol%. Band-edge emission peaks were clearly observed for a crystal grown at 15 mol% Ga composition, while other peaks were hardly observed.