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

Abstract

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-insulatorsemiconductor (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.

RETRACTED ARTICLE: Fundamental Discovery of New Phases and Direct Conversion of Carbon into Diamond and hBN into cBN and Properties

“…In addition, synthesis and scale-up processing of phase-pure cBN by both PVD and CVD methods are still very challenging, only up to~85 pct cBN content has been achieved. [23,25] The PVD methods close to equilibrium lead to the formation of hBN, and the formation of cBN requires highly nonequilibrium processing requiring energetic ion bombardment, localized stress, and high concentration of defects. [26][27][28] These observations tend to favor Corrigan and Bundy phase diagram (curve 1 in Figure 10) showing hBN as the stable phase and cBN metastable in the entire temperature range at ambient pressures.…”

“…In view of the above properties, cBN and diamond represent Holy Grail for solid-state devices and systems, ranging from high-power devices to cutting tools and biomedical applications. [23] Here, we review direct conversion of hBN into cBN, which is analogous to carbon to diamond conversion, by a similar nanosecond pulsed laser melting at ambient temperatures and atmospheric pressure in air in accordance with curve 3 of the phase diagram ( Figure 10). This extension for BN phase diagram is very similar to the one proposed for carbon.…”

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

“…A detailed discussion of the various approaches, along with extensive material characterization and analysis was reviewed by Samantaray and Singh. [151] Because of these c-BN materials challenges, except for an early promising demonstration of a UV emitter, [152] progress toward realizing device technologies has been slow. A recent review of these efforts has been given by Zhang.…”

Research Update: Direct conversion of h-BN into pure c-BN at ambient temperatures and pressures in air

“…However, c-BN coatings have certain advantages over diamond due to higher oxidation resistance than diamond because of protective boron oxide layers. 1,2 Due to less reactivity even at high temperatures with ferrous alloys, c-BN coatings are ideally suited for machining these alloys. The electrical properties of c-BN are quite similar to those of diamond, where c-BN has Johnson (for high-power devices) and Keyes (for integrated circuits) figures of merit 8200 and 32 compared to 1 for silicon.…”

“…In view of the above properties, c-BN and diamond represent Holy Grail for solid state devices and systems, ranging from high-power devices to cutting tools and biomedical applications. 1,2 According to the BN phase diagram, the hBN-cBN-Liquid triple point occurs at 3500 K/ 9.5 GPa or at 3700 K/7.0 GPa according to a recent theoretical refinement. [3][4][5] Thus, phase pure cBN can be synthesized only near the triple point at high temperatures and pressures.…”