NOVELTY - Preparing (M1) polycrystalline group III metal nitride material, comprises: (a) providing source material comprising group III metal and/or group III metal halide into chamber (108); (b) providing getter at a level of at least 100 ppm with respect to source material, into the chamber; (c) transferring nitrogen-containing material into the chamber; (d) heating chamber to a determined temperature; (e) pressurizing chamber to a determined pressure; (f) processing nitrogen-containing material with source material in chamber; and (g) forming polycrystalline group III metal nitride material.    USE - The method is useful for preparing a polycrystalline group III metal nitride material (claimed), where the polycrystalline group III metal nitride material is useful: as a raw material for ammonothermal growth of bulk group III nitride crystals; and for manufacturing bulk or patterned substrates, which are useful in optoelectronic devices, lasers, LEDs, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits or transistors.    ADVANTAGE - The method: provides the polycrystalline nitride material, which is clear and free from haze, and exhibits improved magnetic and luminescent properties; utilizes the getter, which enables the growth of group III nitride single crystals with improved purity; and is simple and cost effective, as compared to conventional methods.    DETAILED DESCRIPTION - Preparing (M1) a polycrystalline group III metal nitride material, comprises: (a) providing a source material comprising a group III metal and/or a group III metal halide into a chamber (108), where the source material comprises at least one metal comprising aluminum, gallium or indium; (b) providing a getter at a level of at least 100 ppm with respect to the source material into the chamber, so that the getter contacts the source material; (c) transferring a nitrogen-containing material into the chamber; (d) heating the chamber to a determined temperature; (e) pressurizing the chamber to a determined pressure; (f) processing the nitrogen-containing material with the source material in the chamber; and (g) forming a polycrystalline group III metal nitride material. An INDEPENDENT CLAIM is also included for forming (M2) a polycrystalline gallium-containing group III metal nitride material, comprising providing a gallium-containing group III metal or a group III metal halide source material to a chamber (where the gallium-containing group III metal or metal halide source material comprises aluminum, gallium or indium), the steps (b)-(f) as above per se to form a polycrystalline gallium-containing group III metal nitride material comprising many grains of a crystalline gallium-containing group III metal nitride, and forming a crystalline gallium-containing group III metal nitride crystal from the polycrystalline gallium-containing group III metal nitride material having a wurtzite structure free from any cubic entities and an optical absorption coefficient of less than or equal to 2 per cm at wavelengths of 405-750 nm, where: the grains has an average grain size of 10 nm to 10 mm and defines many grain boundaries; the polycrystalline gallium-containing group III metal nitride material has an atomic fraction of a gallium-containing group III metal of 0.49-0.55, and an oxygen content in the form of a gallium-containing group III metal oxide or a substitutional impurity within the polycrystalline gallium-containing group III metal nitride material of less than 10 ppm; and many inclusions within the grain boundaries and the grains comprise a getter that constitutes a distinct phase from the crystalline gallium-containing group III metal nitride and is located within individual grains of the crystalline gallium-containing group III metal nitride and/or at the grain boundaries of the crystalline gallium-containing group III metal nitride, and is incorporated into the polycrystalline gallium-containing group III metal nitride at a level of greater than 200 ppm.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a reactor.    Apparatus (100)    Reactor housing wall (104)    Chamber (108)    Energy source (110)    Crucible (120)