Hexagonal Boron Nitride Crystal Growth and Applications
Hexagonal boron nitride BN (hBN) and cubic BN (cBN) are known as the representative crystal structures of BN. The former is chemically and thermally stable, and has been widely used as an electrical insulator and heat-resistant material. The latter, which is a high-density phase, is an ultrahard material second only to diamond. Among those BN crystals, some progress in the synthesis of high purity BN crystals was achieved by using Ba-BN as a growth solvent material at high pressure (HP) of 5.5 GPa. Band-edge natures (cBN Eg=6.2eV and hBN Eg=6.4eV) were characterized by their optical properties. The key issue to obtain high purity crystals is to reduce oxygen and carbon contamination in HP growth circumstances. Then, an attractive potential of hBN as a deep ultraviolet (DUV) light emitter and also superior properties as a substrate of 2-dimensional (2D) atomic layer devices such as graphene were realized. In recent years, h-BN has been applied not only as a 2D substrate material, but also as a low-loss dielectric, an infrared confinement device (phonon polariton), and a host material for quantum sensing such as post NV-diamond.
Also, controlling of boron and nitrogen isotope ratio (10B,11B and 15N) in hBN and cBN crystals can now be carried out by metatheses reaction under HPHT.
In this paper, our recent studies on hBN single crystal growth under HP with respect to impurity controls for exploring new functions will be reported.