Seeded growth of AlN single crystals by physical vapor transport

Seeded growth of AlN single crystals was achieved in an induction-heated, high-temperature reactor. The growth process was based on physical vapor transport (PVT), where presintered AlN powder was used as source material. AlN seeds were cut from a boule containing large single crystalline grains, which were grown by natural grain expansion of an initially polycrystalline, self-seeded deposit. Seeded growth was interrupted several times in order to refill the AlN powder source and a dedicated process scheme was used to ensure epitaxial re-growth on the seed surface after each exposure to air. The single crystalline seed expanded laterally at an angle of 45° resulting in an 18 mm large AlN single crystal. The crystal expansion rate, crystalline orientation, as well as growth morphology were characterized by optical microscopy and X-ray diffraction, respectively.