Polycrystalline III-nitrides

A method for making a polycrystalline III-nitride of high purity and density comprising flowing a halide-containing vapor and a nitrogen-containing vapor into contact with a molten group III-metal by:

• (a) flowing the nitrogen-containing vapor having a first nitrogen flow rate and the halide-containing vapor over the molten group III-metal at a first temperature for a first duration sufficient to form a porous crust in a first flow, wherein the porous crust comprises a plurality of pores, the porous crust covering a portion of an upper surface of the molten group III-metal;
• and
• (b) increasing the first nitrogen flow rate relative to a halide flow rate to obtain a second nitrogen flow rate in a second flow to contact a remaining portion of the molten group III-metal at the porous crust at a second temperature for a second duration sufficient to convert substantially all of the remaining portion of the molten group III-metal to a high density slab comprising the polycrystalline III-nitride, wherein the first temperature and the second temperature are substantially similar, the high density slab having a density of 75 to 99% and being substantially solid throughout.