a. a crucible effective to contain an AlN source material and a growing AlN crystal boule, said crucible having a thin wall thickness in at least that portion housing said growing AlN crystal boule;

b. a mechanical seal sealing an end piece to said crucible, said mechanical seal effective to substantially prevent aluminum vapor diffusion while enabling nitrogen and argon diffusion to thereby maintain a substantially uniform total pressure in the interior and the exterior of said crucible;

c. a susceptor, in case of an inductive heating, or a heater, in case of a resistive heating, made from a material selected from the group consisting of purified graphite solid with an ash content <50 ppm tantalum, tantalum carbide, tantalum nitride, niobium carbide and niobium nitride, all with a purity, by weight, >99.9%;

d. a thermal insulation enclosing said susceptor or heater effective to provide a thermal gradient inside said crucible in the range of 5-100° C./cm, said thermal insulation being a material selected from the group consisting of graphite thermal insulation, rigid or flexible graphite fiber insulation and graphite powder, all with ash content >100 ppm, Ta, TaC, Nb, NbC, TaN, NbN powders, all with a purity, by weight, >99.9; and

e. a furnace chamber capable of being operated from a vacuum (<0.1 torr) to a gas pressure of at least 4000 torr through filling or flowing a nitrogen gas or a mixture of nitrogen gas and argon gas.