In this work we report our observations of naturally grown rotation domains in AlN thin films epitaxially grown on (1) sapphire by hydride vapor phase epitaxy (HVPE), and demonstrate that the Σ-twinning, proposed by coincidence site lattice (CSL) theory, can work as an effective way to release the intrinsic strain and result in the generation of dislocation free crystals. The rotation domains have been observed as irregular-hexagonal inverted prisms which open to the film surface, and their rotation angles, measured by XRD φ -scan of (10 1 3), (10 1 2) or (11 2 4) at Bragg condition respectively, have been verified as 27.7°, 21.8° and 7.1° corresponding to Σ13, Σ7, and Σ61 saperately. Interestingly, no other rotation angles, except CSL-style mis-orientations predicted in hexagonal system, have been observed. The boundary issue, including a twist boundary at bottom and six tilt ones on side planes of Σ-twinning, has been thoroughly discussed based on our transmission electron microscopy studies in methods of two-beam (0, g) contrast imaging, with g=(0002), (11 2 0), and (01 1 0) respectively, to reveal the possible planer defects. Our characterization for more than 5 Σ-twinned regions indicated that (i) in contrast to the matrix AlN crystal where the dislocation density is estimated as 2.8 × 10 10 /cm 2 , there is free of dislocation, stacking faults or any planar defects in rotation domain area; (ii) the rotated prismatic domains are actually encapsulated by a hexagonal cage which is made of complex misfit-dislocation cores, referred to as soliton arrays, which are produced in the formation of Σ-twinned supercells. The optical feature of those boundaries has also been studied by Cathodoluminescence spectroscopy at 8 K. Those unusual and homoepitaxial crystals in size of the dimensions up to 10 microns in height and 3 microns in width, observed in AlN film of above 15 μm thickness, would be valuable in both theoretical studies and practical applications.