Preparation of SiB_4±x and SiB₆ plates by chemical vapour deposition of SiCl₄ + B₂H₆ system

SiB_4±x and SiB₆ plates were prepared by chemical vapour deposition (CVD) using SiCl₄, B₂H₆ and H₂ gases under the conditions of deposition temperatures (T_dep) from 1323–1773 K, total gas pressures (P_tot) from 4–40 kPa and B/Si source gas ratio (m_B/Si=2B₂H₆/SiCl₄) from 0.2–2.8. The effects of CVD conditions on the morphology, structure and composition of the deposits were examined. High-purity and high-density SiB_4±x and SiB₆ plates about 1 mm thick were obtained at the deposition rates of 71 and 47 nm s⁻¹, respectively. The lattice parameter, composition and density of CVD SiB_4±x plates were dependent on their non-stoichiometry. The lattice parameter, a, was 0.6325 nm, but c ranged from 1.262–1.271 nm.The B/Si atomic ratio ranged from 3.1–5.0, and the density ranged from 2.39–2.45×10³ kg m⁻³. The CVD SiB₆ plates showed constant values of lattice parameters (a=1.444 nm, b=1.828 nm, c=0.9915 nm), composition (B/Si=6.0) and density (2.42×10³ kg m⁻³), independent of CVD conditions.