Thermal conduction in lattice-matched superlattices of InGaAs/InAlAs

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 In_0.53Ga _0.47As/In_0.52Al_0.48As SLs grown by metalorganic chemical vapor deposition as a function of SL period thickness (4.2 to 8.4nm) and layer thickness ratio (1:3 to 3:1). Conductivities are measured using time-domain thermoreflectance and vary between 1.21 and 2.31Wm ^-1K^-1. By studying the trends of the thermal conductivities for large SL periods, we estimate the bulk conductivities of In_0.53Ga_0.47As and In_0.52Al_0.48As to be approximately 5Wm^-1K^-1 and 1Wm^-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 ∼0.1m²KGW^-1, and is negligible compared to the intrinsic alloy resistances, even for 2nm 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 In_1-xGa_xAs/In_1-yAl_yAs SL cores.