Bulk GaN single crystal growth and characterization using various alkali metal flux

Bulk GaN single crystal was grown by the flux growth. Using a flux, the solvent-thermal method for growing bulk GaN single crystal requires lower temperature (∼800 °C) and pressure (∼100 atm) than when growing them directly from high-temperature solution. In this study, we investigated the influence of the N₂ pressure and flux ratio on the growth of the bulk GaN single crystals and used 99% pure alkali metal as a flux. The mole fraction of flux/(flux+Ga) was 0.30-0.67. GaN single crystals were synthesized at a temperature of ∼800 °C and an N₂ gas pressure of ∼8 MPa for 200 h. The shape of the single crystals was examined by low magnification microscopy. The hexagonal struture of the GaN single crystals was confirmed by X-ray diffraction. The chemical composition was analyzed by electron probe micro analysis. The amounts of O₂ and N₂ impurities were analyzed by means of an N₂/O₂ determinator. The optical properties of the GaN single crystals were examined using a photoluminescence analyzer, in order to verify their suitability for blue emitting diodes.