Thermal conductivity of crystalline AlN and the influence of atomic-scale defects

Abstract

Aluminum nitride (AlN) plays a key role in modern power electronics and deep-ultraviolet photonics, where an understanding of its thermal properties is essential. Here we measure the thermal conductivity of crystalline AlN by the 3$\omega$ method, finding it ranges from 674 $\pm$ 56 W/m/K at 100 K to 186 $\pm$ 7 W/m/K at 400 K, with a value of 237 $\pm$ 6 W/m/K at room temperature. We compare these data with analytical models and first principles calculations, taking into account atomic-scale defects (O, Si, C impurities, and Al vacancies). We find Al vacancies play the greatest role in reducing thermal conductivity because of the largest mass-difference scattering. Modeling also reveals that 10% of heat conduction is contributed by phonons with long mean free paths, over ~7 $\mu$m at room temperature, and 50% by phonons with MFPs over ~0.3 $\mu$m. Consequently, the effective thermal conductivity of AlN is strongly reduced in sub-micron thin films or devices due to phonon-boundary scattering.