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 materials. The latter, which is a high-density phase, is an ultra-hard material second only to diamond.The color of the cBN crystals were always amber or brownish so far which is attributed by carbon andoxygen impurity. After some struggles for high pressure and high temperature (HPHT) solution growth, we could find suitable solvent of Ba-BN system which gave us almost colorless cBN with band-edge nature. By using similar procedure, high purity hBN crystals were obtained and their attractive potential as a wide-band gap material was realized. It is emphasized that hBN crystals exhibits superior properties as ultra violet light emitter as well as a substrate of graphene devices. The current subject is to realize how the major impurities such as carbon and oxygen affect the properties of hBN and cBN. Also, controlling of boron and nitrogen isotope ratio (¹⁰B,¹¹B and ¹⁵N) in hBN and cBN crystals can be now carried out by methatheisis reaction under HPHT.

In this paper, recent studies for properties of BN single crystals obtained at high pressure with respect to impurity and Boron/ Nitrogen isotope control will be reported.