Physical Principles of Increasing Thermoelectric Figure of Merit in Nanostructured Materials

Abstract

The paper reviews the basic physical principles of improving the thermoelectric quality factor in nanostructured materials such as thin films, superlattices, whiskers, nanoscale structures, quantum wells, quantum wires. The physical fundamentals of optimizing such important parameters of thermoelectric materials as thermoelectric power, electrical resistivity, and thermal conductivity. We have conducted the analysis of the effect of Kapitsa grain-boundary thermal resistance, depending on the type of interfaces: coherent (the presence of elastic strains is possible), semicoherent (misfit dislocations are surrounded by elastic strains), and incoherent (the interaction between phases is minimal), shape and size of inclusions. The thermoelectric power in low-dimensional structures can be increased by changing the form of the density of states near the Fermi level or due to the effect of energy filtering of charge carriers. As part of the increase in the thermopower, the semimetal−semiconductor quantum transition in bismuth and carbonbased nanostructures is considered. The modulation doping of nanostructures allows one to achieve large values of the mobility of charge carriers at their very high concentration, which is demonstrated in the work on the example of superlattices of quantum dots based on silicon and germanium, as well as two-phase composites. Much attention is paid to the analysis of the experimental results, available in literature, which confirm the theoretical conclusions about the possibility of creating highly effective thermoelectric nanomaterials. The main approaches to obtaining nanostructures with the required size and distribution of nanoparticles are briefly considered.