Thin film growth of boron nitride on α-Al2O3 (0 0 1) substrates by reactive sputtering

Highlights: ► A BN film grown on α-Al2O3 (0 0 1) had a structure in which h-BN sheet stacking continued through almost the whole film thickness. ► The structure was characterized by X-ray diffraction, ATR-IR, and XPS. ► Tauc plots suggested the film had direct band gap and the optical band gap was close to that of bulk h-BN. -- Abstract: Boron nitride thin films were grown on α-Al2O3 (0 0 1) substrates by reactive magnetron sputtering. Infrared attenuated total reflection (ATR) spectra of the films gave an intense signal associated with in-plane B-N stretching TO mode of short range ordered structure of BN hexagonal sheets. X-ray diffraction for the film prepared at a low working pressure (ca. 1 × 10−3 Torr) gave a diffraction peak at slightly lower angle than that corresponding to crystal plane h-BN (0 0 2). It is notable that crystal thickness calculated from X-ray peak linewidth (45 nm) was close to film thickness (53 nm), revealing well developed sheet stacking along the direction perpendicular to the substrate surface. When the substrates of MgO (0 0 1) and Si (0 0 1) were used, the short-range ordered structure of h-BN sheet was formed but the films gave no X-ray diffraction. The film showed optical band gap of 5.9 eV, being close to that for bulk crystalline h-BN.