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

TL;DR

This study measures the thermal conductivity of crystalline AlN across temperatures, analyzes the impact of atomic-scale defects, especially Al vacancies, and models phonon contributions to understand heat transfer limitations in devices.

Contribution

It provides detailed experimental data and modeling insights on how atomic-scale defects influence AlN's thermal conductivity, highlighting the role of Al vacancies and phonon mean free paths.

Findings

Thermal conductivity of AlN varies from 674 W/m/K at 100K to 186 W/m/K at 400K.

Al vacancies significantly reduce thermal conductivity due to mass-difference scattering.

Long mean free path phonons contribute substantially to heat conduction, affecting thin film device performance.

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.