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We report on the maskless epitaxial lateral overgrowth (ELOG) of the AlN layer on trench-patterned AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). With a two-phase growth of different V/III ratio at a relatively low growth temperature of 1250 °C, up to a 7.3-μm-thick high-quality crack-free AlN film with a threading dislocation density of 8 × 10⁸ cm^-2 was obtained. Compared with the 0.9-μm AlN film grown on a planar sapphire substrate, the ELOG-AlN film has a lower dislocation density and a much better strain state, regardless of its 7.3-μm thickness. Compared with the single low V/III ratio growth, the two-phase growth method can lead to a coherent coalescence at the second growth stage and hence suppress new dislocations generating at the coalescence fronts. Stimulated emission was observed from Al(Ga)N multi-quantum-wells laser grown on the ELOG-AlN template with low dislocation density. The deep-ultraviolet laser (DUV) on these templates exhibited lasing at 263.3 nm with the spectral linewidth of 1.29 nm and threshold pumping power density of 2.7 MW/cm² at room temperature.