AIN (aluminum nitride) single crystal substrate is expected as high efficiency, high frenquency electronical device and deep ultraviolet emitting element. By using AIN substrate, homoepitaxial growth can be done and defect density of nitride crystal deposition can be controled at a low level. Now, nitride semiconductor substrate like sapphire, is used as substrate material for ultraviolet emission element. It's obvious that AIN is one of the best substrates from the view of lattice mismatch and ultraviolet light penetrative power. However it's difficult to produce AIN single crystal substrate from melt liquid since the melt point is high therefore disassociation voltage will be high as well.