Chapter 4 - Recent progress of boron nitrides

Abstract

Boron nitride occurs in several crystalline phases, among which cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) are two of the most interesting wide bandgap materials from both scientific and practical viewpoints. They have been extensively investigated over many years. Due to their wide bandgap, good thermal conductivity, low dielectric constant, and high breakdown field, c-BN and h-BN are promising candidates for optoelectronic devices operating in the deep-ultraviolet range and for high-temperature and high-power electronic devices operating in harsh environments. This chapter first reviews the current status of the synthesis, properties, and characterizations of c-BN thin films, and then analyzes the growth features and proposed mechanisms of c-BN films. Next, some important progress, including stress relief of thick c-BN films and the epitaxial growth of c-BN films, is described. In recent theoretical and experimental research, several dopants, including Be, Mg, Zn, S, C, and Si, have been incorporated into c-BN thin films during deposition or by post ion implantation, resulting in both n- and p-type conduction. The following section of this chapter critically and comprehensively reviews the current status of the doping and electrical properties of c-BN films. Furthermore, the layered structure of h-BN allows the preparation of ultrathin nanosheets with very smooth surfaces and low defect density, which proved to be useful as supporting substrates and gate dielectric layers in two-dimensional (2D) nanoscale electronics. Apart from h-BN thin films, recent progress in properties, synthesis, and emerging applications of 2D h-BN is also reviewed in the last section.