Review Article: Challenge in determining the crystal structure of epitaxial 0001 oriented sp2-BN films

Abstract

Boron nitride (BN) as a thin film is promising for many future electronic applications. On 0001 α-Al2O3 and 0001 4H/6H-SiC substrates, chemical vapor deposition yields epitaxial sp2-hybridized BN (sp2-BN) films oriented around the c-axis. Here, the authors seek to point out that sp2-BN can form two different polytypes; hexagonal BN (h-BN) and rhombohedral BN (r-BN), only differing in the stacking of the basal planes but with the identical distance between the basal planes and in-plane lattice parameters. This makes structural identification challenging in c-axis oriented films. The authors suggest the use of a combination of high-resolution electron microscopy with careful sample preparation and thin film x-ray diffraction techniques like pole figure measurements and glancing incidence (in-plane) diffraction to fully distinguish h-BN from r-BN.