Crystal growth of GaN from Na-Ga melt in BN containers

A melt of Na and Ga with various Ga contents was placed in a BN crucible and reacted at 650 degrees C for 300 h with N-2 generated from the decomposition of NaN3 in a sealed stainless-steel tube. At 0.25 and 0.45 Ga molar fractions (r(Ga)=Ga/(Ga+Na)), GaN precipitated at the interface of the melt and gas phases, and on the wall and bottom of the crucible. Platelet single crystals with a maximum size of 2 mm grew at the inside of the interface layer. The precipitates on the wall and bottom consisted of hexagonal columnar crystals elongated along the c-axis direction. The size of these crystals was about 10-20 mu m at r(Ga)=0.25 and 50-100 mu m at r(Ga) =0.45. The morphology of the precipitates observed by scanning electron microscopy suggested that the columnar GaN crystals grew from the melt phase. At r(Ga)=0.65 and 0.85, thin GaN microcrystalline layers partially covered the Na-Ga melt surface, but the formation of bulk GaN was not observed in the BN crucible.