Rhombohedral Boron Nitride Epitaxy on ZrB2

Epitaxial rhombohedral boron nitride films were deposited on ZrB₂(0001)/4H-SiC(0001) by chemical vapor deposition at 1485 °C from the reaction of triethylboron and ammonia and with a minute amount of silane (SiH₄). X-ray diffraction (XRD) φ-scans yield the epitaxial relationships of 𝑟−𝐵𝑁(0001)∥𝑍𝑟𝐵2(0001) out-of-plane and 𝑟−𝐵𝑁(1120)∥𝑍𝑟𝐵2(1120) in-plane. Cross-section transmission electron microscopy (TEM) micrographs showed that epitaxial break down of r-BN film occurs approximatively after 10 nm, above which epitaxial growth proceeds only in limited area up to 80 nm of film thickness. Both XRD and TEM demonstrate the formation of carbon- and nitrogen-containing cubic inclusions at the ZrB₂ surface. Quantitative analysis from X-ray photoelectron spectroscopy of the r-BN films shows B/N ratios between 1.30 to 1.20 and an O content of 3 to 4 at.%. Plan-view scanning electron microscopy (SEM) images reveal a surface morphology where an amorphous material comprising B, C, and N is surrounding the epitaxial twinned r-BN crystals. SiH₄ exposure prior to growth was found to reduce the amount of the amorphous phase on the surface. Defects such as pitting were also observed on the ZrB₂ template surface.