High-temperature conductance loss dominated defect level in h-BN: Experiments and first principles calculations

The dielectric properties of hexagonal boron nitride are investigated in detail. The permittivities hold extremely low values ranging from room temperature to 1500 °C, however, the dielectric loss tangents increase rapidly above 1000 °C. At 1500 °C, the dielectric loss tangent is 20 times more than that at room temperature. The first principles calculations show that the boron vacancy (VB) that gives an acceptor energy level near the valence band presents the lowest ionization energy in the investigated defects, and the calculated VB ionization energy agrees with the experimental value. It indicates that the rapid increase in dielectric loss tangents at high temperature is contributed by electrical conductivity produced by VB ionization under thermal excitation.