Dielectric Spectroscopy of Hydrogen-Treated Hexagonal Boron Nitride Ceramics

Hexagonal boron nitride (h-BN) is a critical material for 2D electronic devices and has attracted considerable attention owing to its structural similarity to graphene. However, it is a dielectric and modifying its electrical properties is a challenge. Hydrogenation has been calculated as a potential method, although it is rarely experimentally measured. Here, dielectric spectroscopy of hot-pressed h-BN after various hydrogen treatments has been investigated. Untreated h-BN showed a frequency-independent dielectric constant (4.2 +/- 0.2) and an immeasurably low dielectric loss factor, demonstrating the ideal dielectric nature of h-BN across the 10(3) to 10(10) Hz range. However, hydrogen plasma (H+) treatment in a microwave chemical vapor deposition (CVD) reactor amplified the complex permittivity dramatically, introducing Havriliak-Negami type dispersion (epsilon(s) approximate to 20 +/- 2, epsilon(infinity) approximate to 4.2 +/- 0.2) and a percolating long-range conductivity (similar to 0.32 mS/m). Annealing in molecular hydrogen (H-2) at similar CVD temperatures showed minimal impact, implying that H-2 diffusion is not the cause. Oxygen plasma treatment, however, removes the percolating conductivity but the Debye mechanism remains. This leads to the conclusion that the electrical conductivity of h-BN ceramics can be modified through hydrogenation, using atomic hydrogen. The potential as a tunable wide-band gap semiconductor is highlighted however for insulating dielectric substrate applications; microwave CVD may destroy these desirable properties.