Growth Conditions and Morphology of GaN Single Crystals Fabricated by the Na Flux Method.

GaN single crystals were synthesized by using the Na-Ga melt at 700-850°C and 1-5 MPa of N2 for 200h. The formation of GaN was not observed at 800°C under 1 MPa of N2, and at 850°C and 1.5MPa of N2. GaN single crystals were obtained lower temperatures and/or the higher N2 pressures. The morphology of the crystals tended to change from prismatic to platelet by decreasing the growth temperature and/or increasing N2 pressure. Colorless transparent prismatic single crystals with a size of about 1.0±0.5±0.5mm3 were obtained by adopting a three-step heating process in which the temperature was increased from 750°C at 0.5°C/h to 800°C under 3MPa of N2.