Miscibility Gaps Analysis for BN–Si–C Ternary Material System

Cubic boron nitride (c-BN) is an ultrawide band gap, superhard material with significant potential for applications under extreme temperatures and pressures. Nevertheless, two major challenges hinder its practical utilization in technology: (i) the difficulty in producing high-quality c-BN films, and (ii) the challenge of effectively n- and p-doping its matrix. This theoretical study focuses on investigating the solubility limits of silicon (Si) and carbon (C) in the c-BN and wurtzite BN (WZ–BN) on the basis of the strictly regular solution approximation. These elements are key candidates as n-type dopants in BN, addressing a critical concern in the realization of c-BN based electronics. The calculated Gibbs free energies of binary mixtures within the temperature range of 800–3000 K indicate that the presence of unstable regions, and consequently, miscibility gaps, are a prevalent characteristic of this system. The analysis reveals that the immiscibility gap is influenced not only by temperature, but also by the crystallographic structure. The calculated results of Si solubility limit in BN–Si binary system are in a good agreement with the latest experimental results. The findings presented here are applicable to the fabrication of multicomponent bulk crystals, epitaxial thin films, and nanostructures based on BN–Si–C solid solutions.