Herein, AlN film grown on metal‐organic chemical vapor deposition (MOCVD) AlN template by high‐temperature hydride vapor phase epitaxy (HVPE) is characterized. High‐resolution X‐ray diffraction results show that the crystal quality of the film is improved compared with that of the template. Atomic force microscopy shows that the root mean square roughness value also decreases. Cathodoluminescence spectra show that the main impurities in the epitaxial layer and template are oxygen atoms. Raman spectroscopy and geometric phase analysis show that HVPE AlN samples maintain a compressive stress internally, which is the key to inhibit film cracking. Transmission electron microscope characterization reveals that most of the dislocations at the interface inherit from MOCVD AlN template, incline in the subsequent growth, react with each other, and finally annihilate. The dislocation bending and reduction mechanism are demonstrated.

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Herein, the influence of free‐standing GaN (FS–GaN) substrates with different polarities on the surface morphologies and physical properties of epitaxial Mg‐doped GaN films grown by metal–organic chemical vapor deposition (MOCVD) is investigated. For the Mg‐doped GaN films grown on polar, semipolar, and nonpolar FS–GaN substrates, their surface morphologies vary greatly, which is attributed to the different surface states and growth modes. All films show high crystalline quality and are basically in a stress‐free state. For polar p‐GaN, good ohmic contact is achieved with Ni/Au electrode. For semipolar and nonpolar p‐GaN, there are obvious contact barriers between the p‐GaN and the metal electrodes, and the Mg‐doping concentration may be higher than that of the c‐plane epitaxial GaN according to the intensity ratio of the band edge peak with respect to the ultraviolet luminescence peak in photoluminescence spectra, which will be investigated in the near future.