Abstract

Understanding the relative importance of interface scattering and phonon-phonon interactions on thermal transport in superlattices (SLs) is essential for the simulation of practical devices, such as quantum cascade lasers (QCLs). While several studies have looked at the dependence of the thermal conductivity of SLs on period thickness, few have systematically examined the effect of varying material thickness ratio. Here we study through-plane thermal conduction in lattice-matched In0.53Ga0.47As/In0.52Al0.48As SLs grown by MOCVD as a function of SL period thickness (4.2 to 8.4 nm) and layer thickness ratio (1:3 to 3:1). Conductivities are measured using time-domain thermoreflectance and vary between 1.21 and 2.31 Wm-1K-1. By studying the trends of the thermal conductivities for large SL periods, we estimate the bulk conductivities of In0.53Ga0.47As and In0.52Al0.48As to be approximately 5 Wm-1K-1 and 1 Wm-1K-1 respectively, the latter being an order of magnitude lower than theoretical estimates. Furthermore, we find that the Kapitza resistance between alloy layers has an upper bound of ≈ 0.1 m2K GW-1, and is negligible compared to the intrinsic alloy resistances, even for 2 nm thick layers. A phonon Boltzmann transport model yields good agreement with the data when the alloy interfaces are modeled using a specular boundary condition, pointing towards the high-quality of interfaces. We discuss the potential impact of these results on the design and operation of high-power QCLs comprised of In1-xGaxAs/In1-yAlyAs SL cores.