Incoherent-to-coherent crossover in thermal transport through III–V alloy superlattices

We report on time-domain thermoreflectance measurements of cross-plane thermal conductivity of In0.63Ga0.37As/In0.37Al0.63As superlattices with interface densities ranging from 0.0374 to 2.19 nm−1 in the temperature range 80–295 K. The measurements are complemented by a three-dimensional finite-difference time-domain solution to the elastic wave equation, in which the rms roughness and correlation length at heterointerfaces are varied, and the parameters yielding best agreement with experiment are determined using machine learning. Both experimental measurements and simulations demonstrate the existence of a minimum in the cross-plane thermal conductivity as a function of interface density, which is evidence of a crossover from incoherent to coherent phonon transport as the interface density increases. This minimum persists with increasing temperature, indicating the continued dominance of the temperature-independent interface and alloy-disorder scattering over the temperature-dependent three-phonon scattering in thermal transport through III–V alloy superlattices.