TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: In the method (M1): the getter is provided into a crucible (120) within the chamber together with the source material; the getter is provided at a level of greater than 0.1% (preferably greater than 1%) or at a level of greater than 300 ppm with respect to the source material; the getter is provided to the chamber via a vapor phase; the polycrystalline group III metal nitride material is formed downstream from a crucible containing the source material; at least one component of the chamber is loaded from a glove box before synthesis and the polycrystalline group III metal nitride material is removed from the chamber to the glove box after synthesis without exposure to ambient air; and the determined temperature is 800-1300 degrees C, and the determined pressure is greater than 0.02 GPa. The method (M1) further comprises: supplying a dopant or a dopant precursor to the chamber; contacting the source material with at least one wetting agent comprising bismuth, germanium, tin, lead, antimony, tellurium and/or polonium; and providing an additional getter comprising at least one of scandium, yttrium, a rare earth metal, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, tungsten (all preferred), beryllium, calcium, strontium, barium or molybdenum. The method (M1) further comprises either: cooling the chamber, removing the polycrystalline group III nitride material from the chamber, providing the polycrystalline group III nitride material to an autoclave or a capsule along with ammonia and a mineralizer, and processing the polycrystalline group III nitride material in supercritical ammonia at a temperature of greater than 400 degrees C; or cooling the chamber, removing the polycrystalline group III nitride material from the chamber, providing the polycrystalline group III nitride material to a furnace along with a flux, and processing the polycrystalline group III nitride material in a molten flux at a temperature of greater than 400 degrees C. Preferred Components: The mineralizer comprises at least one of an alkali metal, an alkaline earth metal, chloride, bromide, iodide or fluoride. At least one of a crucible for containment of group III metal, a reactor housing wall (104), a liner for the chamber, a gas inlet to the chamber, a baffle for gas mixing, or a substrate on which the polycrystalline group III metal nitride material is deposited, comprises a material comprising tantalum carbide, silicon carbide or pyrolytic boron nitride. The polycrystalline group III metal nitride material is a polycrystalline gallium-containing group III metal nitride material. The group III metal is a gallium-containing group III metal. The group III metal halide is a gallium-containing group III metal halide. The getter comprises at least one of boron, carbon, scandium, yttrium, rare earth metal (all preferred), alkaline earth metal, titanium, vanadium, chromium, zirconium, niobium, hafnium, tantalum or tungsten, or their nitrides, oxynitrides, oxyhalide or halide. The getter comprises at least one of a hydrocarbon of formula (CwHy), a halo-carbon of formula (CwXz), a halohydrocarbon of formula (CwHyXz), phosgene, thionyl chloride, boron trichloride, diborane, hydrogen sulfide, a halide of alkaline earth metal, boron, carbon, scandium, titanium, vanadium, chromium, yttrium, zirconium, niobium, rare earth metals, hafnium, tantalum or tungsten, or a hydride of alkaline earth metal, boron, carbon, scandium, titanium, vanadium, chromium, yttrium, zirconium, niobium, rare earth metals, hafnium, tantalum or tungsten.w, y, z = greater than 0; andX = F, Cl, Br or I. EXAMPLE - No suitable example given.