Crystal orientation variation of nonpolar AlN films with III/V ratio on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy

This paper reports the crystal orientation variation in the growth of nonpolar AlN films on r -plane sapphire substrates by plasma-assisted molecular beam epitaxy. The high III-V ratio growth condition (high Al flux) preferred single-crystalline a -plane AlN film growth, whereas the low Al flux condition resulted in the formation of an additional crystal orientation. The film grown under high III-V ratio growth condition also showed better crystal quality, as confirmed by x-ray diffraction rocking curve measurements. The a -plane AlN films with misoriented grains formed under lower Al flux showed growth recovery of single-crystalline a -plane AlN film with the increase in Al flux. The suspension of the misoriented structures in the AlN growth process by changing the Al flux implies a controllable transition of different orientations during the growth of nonpolar or semipolar III-nitrides.