Preparation of Bulk AlN Seeds by Spontaneous Nucleation of Freestanding Crystals

Freestanding AlN single crystals are grown in a RF-heated furnace by physical vapor transport (PVT). Three different growth regimes with growth temperatures between 2080--2200 °C result in different crystal habits and very high structural quality. The Rocking curves show $\mathrm{FWHM}< 21$ arcsec in the 0002 and $10\bar{1}0$ Reflection on the as-grown facets. Isometric AlN crystals with sizes up to $10\times 10\times 12$ mm 3 show a zonar structure consisting of a yellowish core area which is grown on the N-polar ($000\bar{1}$) facet and a nearly colorless edge region grown on prismatic $\{10\bar{1}0\}$ facets. In the two growth zones nearly the same C concentrations but different amounts of O and Si are measured by secondary ion mass spectrometry (SIMS). The yellowish core area show a very low defect density ($\mathrm{EPD}\leq 100$ cm -2 ) and a higher deep UV transparency compared to the edge region.