Herein, nitrogen‐polar (N‐polar, (000‐1)) aluminum nitride (AlN) is grown on sapphire substrates with various misorientation angles through metal‐organic vapor phase epitaxy. Moreover, the effect of the sapphire substrates’ misorientation angle on the surface flatness and the crystal quality of N‐polar AlN is studied. The results demonstrate that the surface flatness of the AlN layer improves as the misorientation angle of the sapphire substrates increases. Further, the root mean square of the AlN layer significantly improves to a maximum of 1 nm, in the range of the misorientation angles between 2° and 4°, as compared with the misorientation angle of 0.2° of a conventional substrate. No deterioration in crystallinity is confirmed when an AlN layer is grown on an N‐polar AlN substrate under the same growth conditions as those for the sapphire substrates.

A nitrogen‐polar (N‐polar) AlGaN/AlN high‐electron‐mobility transistor (HEMT) is proposed, and the generation of a 2D electron gas (2DEG) is simulated. The band diagram of N‐polar (Al)GaN/AlN shows the generation of the 2DEG, whereas that of the conventional metal‐polar (Al)GaN/AlN structure shows the generation of a 2D hole gas. Furthermore, the concentration of the 2DEG is considerably high even when the (Al)GaN layer is as thin as a few nanometers. N‐polar AlGaN/AlN is grown on sapphire substrates with a misorientation angle of 2°; furthermore, atomic force microscope measurements in a range of 5 × 5 μm2 demonstrate that the root‐mean‐square value obtained from atomic force microscopy of N‐polar AlGaN is approximately 0.7 nm. N‐polar AlGaN layers with a thickness of approximately 40–60 nm with more than 50% Al content are almost coherently grown on the N‐polar AlN layer with a thickness of approximately 400 nm.

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