Toward Φ56 mm Al-Polar AlN Single Crystals Grown by the Homoepitaxial PVT Method

Crack-free and parasitic-free Al-polar aluminum nitride (AlN) single crystals up to Φ56 mm were iteratively grown by the homoepitaxial physical vapor transport method. The detailed iterative growth processes from the spontaneous AlN boules to Φ56 mm single crystals were presented. Our growth experiments revealed that stable growth of large Al-polar crystals with good structural quality and UV transparency was possible using a pure tungsten setup. For each iteration, the initial expansion angle, which was dominated by the radial temperature gradient (ΔTr), reached 50–60° under our specific growth system and growth conditions and then gradually decreased to 10–20° during the growth process. For all as-grown crystals, mirror-like facets with a step-flow growth mode could be observed. However, the {101̅0} side planes were strongly suppressed when using larger AlN seeds. Material characterization showed that the full width at half maximum of symmetric and asymmetric high-resolution X-ray diffraction rocking curves was 84–144 arcsec and 45–70 arcsec, respectively. The average etch pit density evaluated by preferential chemical etching was approximately 8.5 × 104 cm–2. The optical transmission spectra revealed that the entire wafer exhibited excellent ultraviolet (UV) transparency, with absorption coefficients of 19–29 cm–1 in the UV range of 4.43–4.77 eV (260–280 nm).