Toward Phi 56 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 Phi 56 mm were iteratively grown by the homoepitaxial physical vapor transport method. The detailed iterative growth processes from the spontaneous AlN boules to Phi 56 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 (Delta T-r), reached 50-60 degrees under our specific growth system and growth conditions and then gradually decreased to 10-20 degrees during the growth process. For all as-grown crystals, mirror-like facets with a step-flow growth mode could be observed. However, the {10 (1) over bar0} 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 x 10(4) 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).