To obtain bulk gallium nitride (GaN) single crystals applicable as the substrate for GaN homoepitaxial growth, we have adopted the Na flux method with some modifications. Assuming that a key reaction of this method is nitrogen dissolution into a flux, we considered both the gas composition and the liquid phase composition. The use of ammonia gas had effects in lowering the threshold pressure for the GaN growth compared with the nitrogen gas which had been used in the original Na flux method. The composition change from pure Na to a mixture of Ca and Na for the flux also brought some favorable effects such as lowering the threshold pressure, and an improvement in the crystal transparency. Finally, the liquid phase epitaxy (LPE) technique along with the Na-based flux method led to the growth of bulk GaN single crystals with much lower dislocation densities than the seed crystals.

Keywords: Gallium nitride, GaN, the Na flux method, LPE, bulk, sngle crystal, dislocation density