Thermal conductivity as a metric for the crystalline quality of $SrTiO3$ epitaxial layers

Measurements of thermal conductivity $Λ$ by time-domain thermoreflectance in the temperature range $100<T<300K$ are used to characterize the crystalline quality of epitaxial layers of a prototypical oxide, $SrTiO3$⁠. Twenty samples from five institutions using two growth techniques, molecular beam epitaxy and pulsed laser deposition (PLD), were analyzed. Optimized growth conditions produce layers with $Λ$ comparable to bulk single crystals. Many PLD layers, particularly those that use ceramics as the target material, show surprisingly low $Λ$⁠. For homoepitaxial layers, the decrease in $Λ$ created by point defects correlates well with the expansion of the lattice parameter in the direction normal to the surface.