Enhancing thermal properties of few-layer boron nitride by high-k Al2O3 capping layer

Atomically thin boron nitride (BN) film has attracted increasing attention among two-dimensional materials for the potential application in electronics devices. The thermal properties of few-layer BN nanosheets (∼2.27 nm) on SiO₂/Si substrates have been investigated without and with high-k Al₂O₃ capping layer, using the temperature-dependent and polarized-laser power-dependent Raman spectroscopy measurements. Due to the effect of Al₂O₃ capping layer, Raman spectrum illustrates the blue-shift of frequency from 1364.9 cm⁻¹ to 1367.9 cm⁻¹, and the first order temperature coefficient for E_2g mode of BN layers increases from −0.02243 cm⁻¹/K to −0.06544 cm⁻¹/K. Furthermore, the room-temperature thermal conductivity of BN with Al₂O₃ capping layer is found to be 332.57 W/mK, which is much larger than that of BN without Al₂O₃ capping layer (∼94.51 W/mK). The enhancement is attributed to the interface charges and compressive stress at the interface between BN and Al₂O₃ capping layer, which has been clarified by the first principle calculations. This work is aimed at expanding the applications of BN materials and improving the performances of BN-based devices in thermal properties.