Si Thin Film With Nanohole Structures to Improve Thermoelectric Performance Part 2: Inverse Fishbone Holes

Abstract In recent years, the demand for high-performance thermoelectric materials for device applications has grown significantly. Controlling thermal transport is important for improving performance. A common approach involves using nanoscale structural interfaces to scatter phonons. This method exploits the differences in mean free paths (MFPs) between phonons and electric charge carriers. By introducing nanostructures, propagation of phonons with long MFPs can be selectively suppressed, reducing thermal conductivity without significantly impacting electrical conductivity. Through simulations based on the Boltzmann transport equation (BTE), we have investigated nanoscale structures that enhance thermoelectric performance. In a previous paper, we analyzed the effects of periodically arranged hole shapes and found that an H-shaped structure with notches oriented perpendicularly to the heat flow achieves the highest thermoelectric performance. We referred to such hole shapes as the “Y-direction phonon trap.” In this study, based on the results of our previous research, we developed a new hole design referred to as the “inverse fishbone.” By optimizing the structural parameters of the Y-direction phonon trap in the inverse fishbone structure, we achieved a dimensionless figure of merit more than four times that of pristine thin films.