The process of GaN single crystal growth by the Na flux method with Na vapor

Ga melts were heated in a boron nitride crucible at 800 °C and 5 MPa of N2 for 8–200 h with Na vapor. Colorless and transparent prismatic GaN single crystals grew from a Na–Ga melt which was formed by dissolution of Na from the gas phase. Nitrogen was probably introduced into the melt with Na. The time dependence of the Na fraction (rNa=Na/(Na+Ga)) in the melts and the yields of GaN were investigated. rNa increased to 0.39–0.43 within 100 h, and then became almost constant at this value. The yield of GaN was less than 2% at 50 h. The yield increased linearly with heating time after 75 h, and reached 57% at 200 h. GaN single crystals with a size of 1.5 mm long were obtained on the bottom of the crucible wall. The largest crystals (3.0 mm-long and 1.2 mm-wide) grew at the edges of the melt and of the GaN crystal formation area near the bottom wall of the crucible.