NOVELTY - Growing method of m-plane gallium-containing nitride crystal involves providing a gallium-containing source material, providing a mineralizer, providing at least two gallium-containing nitride seed plates, supporting the at least two seed plates in a seed rack, placing the source material, the mineralizer, and the seed rack supporting the at least two seed plates in a sealable container, introducing a nitrogen-containing solvent into the sealable container, and processing in a supercritical fluid at a temperature of more than 400 degrees C.    USE - Growing method of m-plane gallium-containing nitride crystal used in formation of m-plane gallium-containing nitride wafer used as substrate for optoelectronic/electronic device e.g. light-emitting diode, laser diode, photodetector, avalanche photodiode, transistor, rectifier, thyristor, Schottky rectifier, p-i-n diode, metal-semiconductor-metal diode, high-electron mobility transistor, metal semiconductor field effect transistor, metal oxide field effect transistor, power metal oxide semiconductor field effect transistor, power metal insulator semiconductor field effect transistor, bipolar junction transistor, metal insulator field effect transistor, heterojunction bipolar transistor, power insulated gate bipolar transistor, power vertical junction field effect transistor, cascode switch, inner sub-band emitter, quantum well infrared photodetector, quantum dot infrared photodetector, solar cell, and diode for photoelectrochemical water splitting and hydrogen generation (all claimed).    ADVANTAGE - The method enables efficient and economical growth of m-plane gallium-containing nitride crystal in relatively faster growing direction using seed crystals or plates that are already large in a relatively slow-growing dimension. The seed rack should be easy to load and unload, enable efficient usage of the available crystal growth volume, and minimize breakage and other yield losses of the crystals.    DETAILED DESCRIPTION - Growing method of m-plane gallium-containing nitride crystal involves providing a gallium-containing source material, providing a mineralizer, providing at least two gallium-containing nitride seed plates, supporting the at least two seed plates in a seed rack, placing the source material, the mineralizer, and the seed rack supporting the at least two seed plates in a sealable container, introducing a nitrogen-containing solvent into the sealable container, and processing the source material, the mineralizer, and the at least two seed plates contained in the sealable container in a supercritical fluid at a temperature of more than 400 degrees C. A surface of each of the at least two m-plane gallium-containing nitride crystals has X-ray diffraction rocking curve full-width-half maximum of less than 150 arc-second. Each of the at least two gallium-containing nitride seed plates comprises a large-area surface (710), and a large-area surface (720) opposite the large-area surface (710), where each of the large-area surfaces (710) and each of the large-area surfaces (720) has a minimum lateral dimension of 1 cm or more. The large-area surface (710) of the gallium-containing nitride seed plate (A) comprises an outward facing growth surface, observed by crystallographic orientation (c), and the large-area surface (720) of the gallium-containing nitride seed plate (B) comprises an outward facing growth surface observed by crystallographic orientation (d), where the crystallographic orientation (c) and the crystallographic orientation (d) differ by 0.1 degrees or more and less than 5 degrees . The crystallographic orientation (c) and the crystallographic orientation (d) are nominally m-plane crystallographic orientation with a miscut angle in the c-direction between 0.05-5 degrees toward (0001) and a miscut angle in the a-direction of 1 degrees or less.    DESCRIPTION OF DRAWING(S) - The drawing shows a Schematic view of wedge-shaped seed plate.    Seed crystals (702)    Large-area surfaces (710,720)