Abstract: A method and apparatus for producing bulk single crystals of AlN having low dislocation densities of about 10,000 cm?2 or less includes a crystal growth enclosure with Al and N2 source material therein, capable of forming bulk crystals. The apparatus maintains the N2 partial pressure at greater than stoichiometric pressure relative to the Al within the crystal growth enclosure, while maintaining the total vapor pressure in the crystal growth enclosure at super-atmospheric pressure. At least one nucleation site is provided in the crystal growth enclosure, and provision is made for cooling the nucleation site relative to other locations in the crystal growth enclosure. The Al and N2 vapor is then deposited to grow single crystalline low dislocation density AlN at the nucleation site. High efficiency ultraviolet light emitting diodes and ultraviolet laser diodes are fabricated on low defect density AlN substrates, which are cut from the low dislocation density AlN crystals.

Abstract: Fabrication of doped and undoped stoichiometric polycrystalline AlN ceramics with high purity is accomplished by, for example, reacting Al pellets with nitrogen gas. Such polycrystalline AlN ceramics may be utilized in the fabrication of high purity AlN single crystals, which may be annealed to enhance a conductivity thereof.

Abstract: Fabrication of doped AlN crystals and/or AlGaN epitaxial layers with high conductivity and mobility is accomplished by, for example, forming mixed crystals including a plurality of impurity species and electrically activating at least a portion of the crystal.

Abstract: Reducing the microvoid (MV) density in AlN ameliorates numerous problems related to cracking during crystal growth, etch pit generation during the polishing, reduction of the optical transparency in an AlN wafer, and, possibly, growth pit formation during epitaxial growth of AlN and/or AlGaN. This facilitates practical crystal production strategies and the formation of large, bulk AlN crystals with low defect densities—e.g., a dislocation density below 104 cm?2 and an inclusion density below 104 cm?3 and/or a MV density below 104 cm?3.

Abstract: Bulk single crystals of AlN having a diameter greater than about 25 mm and dislocation densities of about 10,000 cm?2 or less and high-quality AlN substrates having surfaces of any desired crystallographic orientation fabricated from these bulk crystals.

Abstract: Fabrication of AlN substrates suitable for epitaxial deposition of high-quality nitride-based compounds thereon having at least one single-crystal and substantially planarized useful area exceeding about 1 cm2 with a peak-to-valley surface topography in the useful area being less than about 50 nm is accomplished by, for example, employing an active solution that reacts non-selectively with the substrate material.

Abstract: A method and apparatus for producing bulk single crystals of AlN having low dislocation densities of about 10,000 cm?2 or less includes a crystal growth enclosure with Al and N2 source material therein, capable of forming bulk crystals. The apparatus maintains the N2 partial pressure at greater than stoichiometric pressure relative to the Al within the crystal growth enclosure, while maintaining the total vapor pressure in the crystal growth enclosure at super-atmospheric pressure. At least one nucleation site is provided in the crystal growth enclosure, and provision is made for cooling the nucleation site relative to other locations in the crystal growth enclosure. The Al and N2 vapor is then deposited to grow single crystalline low dislocation density AlN at the nucleation site. High efficiency ultraviolet light emitting diodes and ultraviolet laser diodes are fabricated on low defect density AlN substrates, which are cut from the low dislocation density AlN crystals.

Abstract: A crucible for growing III-nitride (e.g., aluminum nitride) single crystals is provided. The crucible includes an elongated wall structure defining an interior crystal growth cavity. Embodiments include a plurality of grains and a wall thickness of at least about 1.5 times the average grain size. In particular embodiments, the crucible includes first and second layers of grains the first layer including grains forming an inside surface thereof and the second layer being superposed with the first layer. The crucible may be fabricated from tungsten-rhenium (W—Re) alloys; rhenium (Re); tantalum monocarbide (TaC); tantalum nitride (Ta2N); hafnium nitride (HfN); a mixture of tungsten and tantalum (W—Ta); tungsten (W); and combinations thereof.