NOVELTY - A method for growth of gallium-containing nitride crystal involves providing at least two first and second seed plates; supporting two plates in first and second sites of seed rack, the first and second plates having equivalent crystallographic orientation to within five degrees, each of first and second plate having at least 1 cm length; placing gallium-containing source material, mineralizer and plates in sealable container; introducing nitrogen containing solvent; and processing material, mineralizer and plates in supercritical fluid at higher than 400 degrees C and higher than 2 kbar.    USE - For growth of gallium-containing nitride crystal (claimed) for manufacturing bulk or patterned substrates used for a variety of applications including optoelectronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors.    ADVANTAGE - The method is scalable up to very large volumes and is cost effective; enables a cost-effective high pressure apparatus for growth of crystals such as GaN, AlN, InN, InGaN, and AlInGaN and others; can operate with components that are relatively simple and cost effective to manufacture; can be manufactured using conventional materials and/or methods; and enables cost-effective crystal growth and materials processing under extreme pressure and temperature conditions in batch volumes larger than 0.3 liters, larger than 1 liter, larger than 3 liters, larger than 10 liters, larger than 30 liters, larger than 100 liters, and larger than 300 liters.    DETAILED DESCRIPTION - A method for growth of a gallium-containing nitride crystal, involves: (a) providing gallium-containing source material; (b) providing a mineralizer; (c) providing at least two seed plates, including a first seed plate and a second seed plate; (d) supporting the first seed plate and the second seed plate in a first site and a second site of a seed rack, the first seed plate and the second seed plate having substantially an equivalent crystallographic orientation to within five degrees, each of the first seed plate and the second seed plate having a length of at least 1 centimeter; (e) placing the source material, mineralizer, and seed plates in a sealable container; (f) introducing a nitrogen containing solvent into the sealable container; and (g) processing the source material, mineralizer, and seed plates contained in the sealable container in a supercritical fluid at higher than 400 degrees C and a pressure higher than 2 kbar.