Effect of phase and interfacial structure on thermal transport in BN/diamond heterostructures

Cubic BN (c-BN) is attractive for high-power and extreme-environment electronics. However, thin-film synthesis is challenging due to its propensity to form mixed-phase microstructures of sp2-and sp3-bonded polytypes. We combine time-domain thermoreflectance and time-resolved magneto-optic Kerr effect measurements to determine the effect phase composition, bond disorder, and interfacial structure have on thermal transport of BN thin-films grown on boron-doped diamond by plasma-enhanced chemical vapor deposition. High-resolution transmission electron microscopy reveals BN film grown on (001) diamond is turbostratic (t-BN), while the film grown on (111) diamond is c-BN. At 300 K, the t-BN film has a thermal conductivity of 17 ± 2.5 W m−1 K−1, while the c-BN film has a graded conductivity that varies between 5 and 20 W m−1 K−1 as a function of depth. The c-BN film’s thermal conductivity is ≈ 40× lower than that of bulk c-BN, indicating that defects limit phonon mean-free-paths to ∼10 nm. The c-BN/diamond interface conductance is ≈300 +/− 140/100 MW m−2 K−1, about threefold higher than t-BN/diamond. We credit this factor of three difference to interfacial bonding caused in the sp2 vs sp3 bonded polytypes.