The process technologies of AlN growth by physical vapour transport are reviewed in this paper with a focus on the growth parameters, crucible materials, and the type of seeding/nucleation. In this context the three growth strategies for the first generation of AlN seeds, (i) grain selection, (ii) heteroepitaxially seeding on SiC, and (iii) spontaneous nucleation, are evaluated regarding their impact on the structural properties and the sizes of the grown AlN crystals. Major issues for subsequent homoepitaxial growth runs with controlled diameter enlargement, such as thermal field design and seed fixation, are addressed. Furthermore, the influences of the growth conditions on the main optical absorption bands in AlN are discussed.

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 FWHM < 21 arcsec in the 0002 and 101̄0 Reflection on the as-grown facets. Isometric AlN crystals with sizes up to 10 × 10 × 12mm3 show a zonar structure consisting of a yellowish core area which is grown on the N-polar (0001̄) facet and a nearly colorless edge region grown on prismatic {101̄0} 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 (EPD ⩽ 100 cm−2) and a higher deep UV transparency compared to the edge region.

In this paper, the optimal growth conditions during the physical vapour transport of bulk AlN crystals are evaluated with regard to significantly increased deep UV transparency, while maintaining the high structural quality of the AlN crystals which are grown on N-polar c-facets. We show that carbon concentration [C], oxygen concentration [O], and the ratio between both concentrations [C]/[O] have a significant influence on the deep UV transparency. At 3[C] < [O] with [C] + [O] < 1019 cm−3, deep UV transparent AlN single crystals with absorption coefficients at around 265 nm (α265nm) smaller than 15 cm−1 can be prepared. These conditions can be achieved in the N-polar grown volume parts of the AlN crystals using growth temperatures in the range of TG = 2030–2050 °C and tungsten and tantalum carbide as getter materials for carbon and oxygen, respectively. Deep UV transparent AlN substrates (α265nm < 30 cm−1) ≥10 mm in diameter and of high crystalline perfection (rocking curve FWHM < 15 arcsec) are shown for the first time

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