<u>The Role of Interfaces in the Thermal Transport in InAlAs/InGaAs Superlattices</u>

Superlattices (SLs) of ternary alloys In_xAl_1-xAs and In_xGa_1-xAs are used in many emerging technologies, such as light conversion devices and quantum cascade lasers. Proper thermal management in these devices is difficult because the relative importance of phonon scattering in the bulk alloys versus phonon scattering at SL interfaces is not well understood. Using the three omega method, we measure the thermal resistivity of bulk films of InAlAs, InGaAs, as well as SLs of the two materials. These measurements enable us to quantify how alloy concentration of the bulk materials, phonon mode mismatch, and interface roughness between layers affect the SL resistivity. We find that interface effects account for 20% of the resistance of our lattice-matched SLs and 40% of the resistance of In_.3Al_.7As/In_.75Ga_.25As SLs. This result demonstrates a counterintuitive property for these SLs, despite the fact that the resistivity of the bulk alloys in the SL may decrease as the alloy concentrations move away from lattice matched (x~.5 for both materials), the total SL thermal resistance actually increases due to worsening phonon mode mismatch and roughness at the interfaces.