Thermal conductivity and optical phonon scattering of CMOS compatible aluminum nitride based ferroelectric thin films.

The emergence of ferroelectricity in doped aluminum nitride has positioned wurtzite nitrides as promising candidates for next-generation memory and logic devices. However, the structural modifications required to induce and stabilize ferroelectricity, including changes in bond strength, harmonicity, and crystal order, also affect phonon dynamics, creating competing pathways for polarization reversal and thermal transport. In this work, we report the contrasting roles of dopants in governing ferroelectric and thermal properties in Al1-xBxN and Al1-x-yBxScyN thin films where changes in composition and thickness are explored. Using time-domain thermoreflectance, the thermal conductivity reveals dopant-driven transitions between phonon-phonon, phonon-impurity, and defect-induced scattering regimes. Infrared variable-angle spectroscopic ellipsometry provides access to optical phonon lifetimes, and we show a monotonic relationship between cross-plane transverse optical phonon lifetime and cross-plane thermal conductivity measured by time-domain thermoreflectance, indicating that infrared ellipsometry can serve as a system-specific spectroscopic probe of disorder-induced vibrational damping in these aluminum nitride based ferroelectric films. The findings demonstrate that while disorder can reduce coercive fields, the same mechanism simultaneously suppresses lattice thermal conductivity, underscoring the inherent trade-off between ferroelectric performance and thermal management. This work highlights the dual, and at times conflicting, role of dopants in aluminum nitride based ferroelectrics that shape both electronic and thermal responses, defining thermal-design constraints for integrated thermally resilient electronic systems.