NOVELTY - Growing crystalline gallium-containing nitride using seed racks involves providing autoclave comprising seed rack device, gallium-containing feedstock in one zone, and at least one seed in seed rack device in another zone; introducing solvent capable of forming supercritical fluid into one and other zone; processing portions of gallium-containing feedstock in supercritical fluid to provide supercritical solution comprising gallium containing species at first temperature; and growing crystalline gallium-containing nitride material from supercritical solution on seed at second temperature.    USE - For growing a crystalline gallium-containing nitride, useful in optoelectronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors,    ADVANTAGE - The method uses a cost-effective high pressure apparatus for growth of crystals such as gallium nitride, aluminum nitride, indium nitride, indium gallium nitride, and aluminum indium gallium nitride. The method operates with components that are relatively simple and cost effective to manufacture. The method utilizes conventional materials and/or methods and enables cost-effective crystal growth and materials processing under extreme pressure and temperature conditions.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) system for growing crystalline gallium-containing nitride using seed racks, comprising an autoclave comprising first zone and second zone, gallium-containing feedstock in the first zone; seed rack provided within vicinity of the second zone; sites numbered from 1 through N, where N is an integer greater than 2, disposed spatially from a first portion of the seed rack to a second portion of the seed rack, each of the sites is configured to mechanically support at least one seed; and    (2) method of crystal growth involving providing an apparatus for high pressure crystal or material processing, the apparatus comprising a cylindrical capsule region comprising a first region and a second region, and a length defined between the first region and the second region; an annular heating member enclosing the cylindrical capsule region; at least one annular ceramic or metal or cermet member having a predetermined thickness disposed around a perimeter of the annular heating member, the annular member is made of material having a compressive strength of about 0.5 GPa and greater and a thermal conductivity of less than or equal to 100 watts per meter-Kelvin, and high strength enclosure material disposed overlying the annular ceramic member; providing capsule containing seed rack, baffle, solvent, mineralizer, gallium-containing raw material, and at least first seed and second seed provided on a first site and a second site of seed rack; and placing the capsule within an interior region of the cylindrical capsule region; and processing the capsule with thermal energy to cause an increase in temperature within the capsule to greater than 200 degrees C to cause the solvent to be superheated.