Thermoelectric properties of Si/SiC thin-film superlattices grown by ion beam sputtering

Abstract

There are many mechanical systems that convert heat to work and processes that utilize heat including power plants, automobiles, and foundries. Most of these systems expel large amounts of waste heat to the environment that goes unused. One way of recovering the waste heat is to use a solid-state energy converter based on thermoelectric processes. Nano-scaled materials are of interest for use in thermoelectric devices because their properties enhance the efficiency over those obtained using bulk materials. Some nano-scaled materials systems being considered are thin-film superlattices that utilize quantum confinement effects. Thin-film, superlattice thermoelectric devices could revolutionize traditional heat-to-work systems and heat-only processes if they are coupled to the systems to recycle a fraction of the waste heat into usable power. The advantage of thermoelectrics over traditional mechanical systems is that they use solid-state processes instead of moving parts and working fluids. As a result, they can be made to be more reliable and require less maintenance. This thesis focuses on the characterization of a thin-film, superlattice (SL) thermoelectric material formed by alternating silicon and silicon carbide layers to form an n-type quantum well. Superlattices of 31 bi-layers of Si/SiC (10 nm each) were deposited on silicon, quartz, and mullite substrates using a high-speed, ion-beam sputter deposition process, and the Seebeck coefficient and electrical resistivity are measured as a function of temperature and used to compare film performance. In addition, SL layer thicknesses of 2 and 5 nm were deposited on mullite to determine the effect layer thickness has on the thermoelectric properties.