Dielectric Spectroscopy of Hydrogen-Treated Hexagonal Boron Nitride Ceramics
Jerome A. Cuenca, Soumen Mandal, David Morgan, Malcolm Snowball, Adrian Porch, Oliver A. Williams
Abstract
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 103 to 1010 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 (εs ≈ 20 ± 2, ε∞ ≈ 4.2 ± 0.2) and a percolating long-range conductivity (∼0.32 mS/m). Annealing in molecular hydrogen (H2) at similar CVD temperatures showed minimal impact, implying that H2 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.