Review of synthesis and properties of cubic boron nitride (c-BN) thin films

Cubic boron nitride (c-BN) thin films are of significant interest because of their diamond like structure and properties. c-BN shows high thermal conductivity, chemical inertness against ferrous metals even at high temperatures, wide band gap, and good transmittance over a wide spectral range from UV to visible. Applications of c-BN include hard protective coatings for cutting tools, in optical instruments as UV detectors, as emitters, and in high temperature electronic devices. However, synthesis of phase pure c-BN thin films continues to be very challenging. The present study reviews the current status of the synthesis, characterisation, mechanical, electrical, and optical properties of c-BN thin films. Both physical and chemical vapour deposition methods used for the preparation of the c-BN films are covered. In addition, different nucleation and growth models of c-BN formation and growth on different substrates are described. The influence of process parameters such as ion energy, growth temperatures, chemical precursors, bias, and impurities on the nucleation and growth is reviewed. Mechanical properties including hardness, elastic modulus, and stiffness of c-BN films are discussed. The latest developments in electrical properties of the c-BN films based on metal - insulator semiconductor (MIS) hetero-structures, interface states, impurity states, conduction mechanism, field emission properties, and negative electron affinity (NEA) are presented. The optical properties and cathodoluminescence characteristics of BN films are also discussed.