A bulk nitride mono-crystal according to claim 29, wherein a seed and the bulk nitride mono-crystal consist essentially of gallium nitride and the seed is an form of a flat plate with two parallel faces perpendicular to c-axis of hexagonal lattice of gallium-containing nitride, (0001) and (000-1), while two bulk mono-crystals of gallium nitride are crystallized on both such faces of the seed cryst