Thermal and Thermoelectric Transport in Semiconductor Nanostructures

During the last decade or so we have witnessed tremendous advancement in characterization and understanding of thermal transport in nanostructures, particularly in the ‘phonon boundary scattering’ regime where the characteristic size of nanostructures ranges from tens to hundreds nanometers and is comparable to phonon mean free path. This understanding is the key underlying reason for improved performance observed in nanostructured thermoelectric materials. However, it is increasingly clear that the boundary scattering mechanism may soon reach its limit and new mechanisms for improving thermoelectric performance need to be explored. One of the opportunities may arise from the study of thermal transport in the so-called ‘confinement’ regime, where the characteristic size of nanostructures is below 10-20 nanometers and is comparable to phonon wavelength. In this work, we will discuss our recent work on using rationally designed nanostructures to study nanoscale thermal and thermoelectric transport phenomena in this regime. We will describe the instrumentation we have been developing that enables the characterization of thermal transport and related properties of these nanostructures and discuss and interpret the measurement results.