Research on Si based thermoelectric material by nanostructuring

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The objective of this research is investigation of the possibility of enhancement of the thermoelectric conversion efficiency of nanostructured Si, which has low environmental load. The key is control of phonon transport, which results in higher performance by reducing the thermal conductivity.We challenged the artificial control of thermal conductivity on the basis of phononics. Formation technology of as small as 100-nm-period air-suspended Si nanostructure has been developed. A high through put and reliable time-domain micro thermoreflectance system for thermal conductivity measurements for micro/nano structures has been developed. We have succeeded in observing a characteristic ballistic phonon transport at room temperature in nanostructures and clear reduction in thermal conductivity in phononic crystal nanostructures compared with those in nanowires. This result shows that this structure is useful for thermal conduction engineering.