Thermal transport in nanoscale semiconductors

摘要

More than 80% of current world energy is generated by burning fossil fuels and more than 60% of this energy is wasted in the form of heat. Converting waste heat into electricity based on thermoelectric (TE) devices/systems is of great interest due to their simplicity, reliability and environmentally benign features. The main limiting factor for the vast application of thermoelectric devices is the inadequate thermoelectric properties: dimensionless thermoelectric figure of merit (ZT). ZT is defined as, (ZT= S~2 σ T/κ) where σ, k, S and T stand for electrical conductivity, thermal conductivity, Seebeck coefficient and absolute temperature, respectively. Up to now, the best commercialized thermoelectric material (bismuth telluride based alloy) has a ZT of only around one at room temperature, whereas a higher ZT will make TE devices more efficient. Over the last decade, we have witnessed the successful efforts of enhancing ZT beyond the unity in complex and nanos-tructured thermoelectric materials by reducing the thermal conductivity (κ) via phonon scattering and/or enhancing the power factor (S~2σ) through quantum confinement, modulation doping, energy filtering, and other new mechanisms by low-bandgap semiconductor materials.