Quasi-ballistic thermal transport in Al0.1Ga0.9N thin film semiconductors

We investigate thermal transport in high-quality Al0.1Ga0.9N thin films grown using plasma-assisted molecular beam epitaxy by time-domain thermoreflectance (TDTR) in the 100 K–500 K temperature range. The apparent thermal conductivity at 300 K and 500 K drops by 30% when the laser modulation frequency is increased from 0.8 MHz to 10 MHz. Tempered Lévy analysis of the quasi-ballistic heat conduction reveals superdiffusion exponents α ≈ 1.70 ± 0.06 at room temperature and α ≈ 1.83 ± 0.16 at 500 K. We describe limitations in concurrent extraction of other model parameters and also discuss the impact of boundary scattering in the 100 K–200 K temperature range.