Can Boron Nitride Conduct Electricity?

Boron nitride is a widely used covalent compound known for its hardness, which is comparable to that of diamond. It combines high strength with a lightweight structure. Its notable thermal conductivity, excellent thermal stability, impressive tensile strength, and electrical insulation properties make it a reliable choice for diverse industrial applications.¹

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Types of Boron Nitride

The two main types of boron nitride used in industry are hexagonal boron nitride (h-BN) and cubic boron nitride (c-BN).

h-BN, particularly in its 2D form, is a stable material with electrical insulating properties. Its structure is similar to graphene, consisting of a flat, layered morphology with the same crystal arrangement.² However, despite these structural similarities, h-BN is a wide-bandgap semiconductor and acts as an insulator at room temperature, whereas graphene functions as a conductor under the same conditions.³

c-BN, on the other hand, is comparable in hardness to diamond. It has greater chemical reactivity and higher thermal stability than many carbon-based compounds.⁴ Additionally, c-BN exhibits high thermal conductivity and remains chemically stable even at elevated temperatures. These characteristics make it suitable for coatings, cutting tools, and high-temperature optical devices.⁵

Electrical Conductivity

The strong covalent bonding between boron and nitrogen results in the absence of free electrons, making boron nitride an insulator at room temperature. Experimental studies have measured the bandgap of h-BN to range between 3.6 and 7.1 eV.⁶

Various experimental studies have investigated the insulating properties of boron nitride. Boron nitride fillers have been incorporated into composites, particularly in the electronics industry, to enhance heat dissipation and improve thermal performance.

However, adding boron nitride to a polybutylene terephthalate matrix was found to significantly reduce the electrical conductivity of the composite.⁷ Researchers concluded that boron nitride fillers disrupt electron transport in the composite, thereby increasing electrical insulation.

Zinc Doping for Improved Conductivity

Zinc doping has been shown to improve the electrical conductivity of both h-BN and c-BN. In an experimental study, both types of boron nitride were deposited on a fused silica substrate using sputter doping, where a 120 mm zinc rod was introduced into the plasma. The zinc concentration in the compound was controlled between 0 % and 4 %.

The initial electrical conductivity of both boron nitride types was less than 1 * 10^-8 Ω^-1 cm^-1. With zinc doping at a concentration of approximately 20,000 ppm, the electrical conductivity improved to 1 * 10^-2 Ω^-1 cm^-1. An increase in zinc concentration also correlated with a reduction in the activation energy for electrical conduction. These findings indicate that zinc doping is an effective method for enhancing the electrical conductivity of both h-BN and c-BN.⁸

Doping h-BN Nanosheets for Microelectronics

Hexagonal boron nitride nanosheets (h-BNNs) are often referred to as “white graphene” due to their structural similarity to graphene. By doping h-BNNSs with specific elements, their band gap can be reduced, allowing a transition from an insulating to a semiconducting state. In one study, fluorinated h-BNNs were produced by introducing fluorine into exfoliated BNNs derived from bulk boron nitride to explore their electrical conductivity.

The doping process resulted in fluorinated exhibiting semiconductor characteristics, with current values ranging from -15.9 to 13.7 µA. In contrast, the pristine BNNSs did not conduct electricity, confirming their inherent insulating properties.⁹ The study demonstrated that selecting appropriate doping materials and methods can effectively modify boron nitride properties, shifting them from insulating to semiconducting behavior.

Regulating n-Type Conductivity in c-BN

Regulating n-type electrical conductivity in boron nitride is a complex challenge that requires extensive research. Recently, researchers have explored silicon doping as a method to enhance and control the electrical conductivity of c-BN. Silicon doping introduces free electrons into the c-BN layers.

This process was implemented using epitaxial growth, where a thin material layer is grown on a substrate while maintaining alignment between the crystalline structures of both materials. Ion-beam-assisted molecular beam epitaxy (MBE) was employed to achieve enhanced electrical conductivity in c-BN.

The ionization energy of silicon donor ions in c-BN was measured at 0.24 eV, indicating that silicon can readily donate electrons to boron nitride, thereby improving its electrical conductivity. By adjusting the silicon concentration, researchers varied the resistivity of c-BN from 1 × 10⁸ Ω·cm in undoped layers to 260 Ω·cm in silicon-doped layers with a doping concentration of 1.5 × 10¹⁹ cm⁻³. This controlled doping process makes silicon a suitable choice for applications in high-temperature electronics and optical devices.¹⁰

In summary, while boron nitride is an insulator at room temperature, its electrical conductivity can be enhanced by introducing impurities through precise doping methods. Careful control of the doping process and materials is essential for improving boron nitride’s conductivity for use in electronic applications.

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References and Further Reading

1. Zhang, H, et al. (2023). Applications and theory investigation of two-dimensional boron nitride nanomaterials in energy catalysis and storage. EnergyChem. https://doi.org/10.1016/j.enchem.2023.100108
2. Zhang, K., et al. (2017). Two dimensional hexagonal boron nitride (2D-hBN): synthesis, properties and applications. Journal of Materials Chemistry C. https://doi.org/10.1039/C7TC04300G
3. Wang, J., et al. (2017). Electrical properties and applications of graphene, hexagonal boron nitride (h-BN), and graphene/h-BN heterostructures. Materials Today Physics. https://doi.org/10.1016/j.mtphys.2017.07.001
4. Vel, L., et al. (1991). Cubic boron nitride: synthesis, physicochemical properties and applications. Materials Science and Engineering: B. https://doi.org/10.1016/0921-5107(91)90121-B
5. Samantaray, C., et al. (2005). Review of synthesis and properties of cubic boron nitride (c-BN) thin films. International Materials Reviews. Available at: https://doi.org/10.1179/174328005X67160
6. Solozhenko, V. (2001). Bandgap energy of graphite-like hexagonal boron nitride. Journal of Physics and Chemistry of Solids. https://doi.org/10.1016/S0022-3697(01)00030-0
7. Ng, H., et al. (2005). Thermal conductivity, electrical resistivity, mechanical, and rheological properties of thermoplastic composites filled with boron nitride and carbon fiber. Polymer Composites. https://doi.org/10.1002/pc.20076
8. Nose, K., et al. (2006). Electric conductivity of boron nitride thin films enhanced by in situ doping of zinc. Applied physics letters. https://doi.org/10.1063/1.2354009
9. Xue, Y., et al. (2013). Excellent electrical conductivity of the exfoliated and fluorinated hexagonal boron nitride nanosheets. Nanoscale Res Lett 8. Available at: https://doi.org/10.1186/1556-276X-8-49
10. Hirama, K., et al. (2020). Control of n-type electrical conductivity for cubic boron nitride (c-BN) epitaxial layers by Si doping. Applied Physics Letters. https://doi.org/10.1063/1.5143791

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