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.
Highlights
INTRODUCTIONBoron nitride (BN) as a thin film is promising for many future electronic applications. From chemical vapor deposition (CVD) and using triethylboron, B(C2H5), and ammonia, NH3, epitaxial growth of sp2-hybridized boron nitride (sp2-BN) has been carried out mainly on 0001 a-Al2O3 and 0001 4H/6H-SiC substrates, yielding films oriented around the c-axis. The processes developed for epitaxial growth requires temperatures in the range of 1100–1500 C, motivating the choice of substrates
From chemical vapor deposition (CVD) and using triethylboron, B(C2H5)3, and ammonia, NH3, epitaxial growth of sp2-hybridized boron nitride has been carried out mainly on 0001 a-Al2O3 and 0001 4H/6H-SiC substrates, yielding films oriented around the c-axis
For a powder sample of polycrystalline sp2-Boron nitride (BN), determination of the crystal structure is straightforward from x-ray diffraction (XRD) in h-2h geometry,12,19–21 whereas for epitaxial sp2-hybridized BN (sp2-BN) films, this distinction is more difficult due to the choice of substrates resulting in predominantly 0001 oriented films
Summary
Boron nitride (BN) as a thin film is promising for many future electronic applications. From chemical vapor deposition (CVD) and using triethylboron, B(C2H5), and ammonia, NH3, epitaxial growth of sp2-hybridized boron nitride (sp2-BN) has been carried out mainly on 0001 a-Al2O3 and 0001 4H/6H-SiC substrates, yielding films oriented around the c-axis. The processes developed for epitaxial growth requires temperatures in the range of 1100–1500 C, motivating the choice of substrates. From chemical vapor deposition (CVD) and using triethylboron, B(C2H5), and ammonia, NH3, epitaxial growth of sp2-hybridized boron nitride (sp2-BN) has been carried out mainly on 0001 a-Al2O3 and 0001 4H/6H-SiC substrates, yielding films oriented around the c-axis.. For a powder sample of polycrystalline sp2-BN, determination of the crystal structure is straightforward from x-ray diffraction (XRD) in h-2h geometry, whereas for epitaxial sp2-BN films, this distinction is more difficult due to the choice of substrates resulting in predominantly 0001 oriented films. We seek to point to the impossibility to apply XRD in h-2h geometry, low magnification transmission electron microscopy (TEM), Raman and Fourier transform IR spectroscopy for structure determination of epitaxial c-axis oriented sp2-BN films. We suggest a combination of advanced thin film x-ray diffraction techniques like pole figure measurements and glancing incidence (in-plane) (GI) diffraction and high-resolution electron microscopy (HREM) with careful sample preparation to distinguish h-BN from r-BN
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