Four-probe thermal and thermoelectric transport measurements of bismuth antimony telluride, silicon, and boron arsenide nanostructures
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Thermal management in electronic devices has become a significant challenge because of the high power density in nanoelectronic devices. This challenge calls for a better understanding of thermal transport processes in nanostructures and devices, as well as new thermal management approaches such as high thermal conductivity materials and efficient on-chip thermoelectric coolers. While several experimental methods have been developed to investigate size-dependent thermal and thermoelectric properties, there are a number of limitations in the current experimental capability in probing nanoscale thermal and thermoelectric transport properties. Among these limitations is the difficulty in determining and eliminating the contact thermal resistance error so as to obtain the intrinsic thermal and thermoelectric properties of nanostructures. This dissertation presents an effort to develop new experimental methods for uncovering the intrinsic thermal and thermoelectric properties of nanostructures, and the applications of these methods for investigating the thermal and thermoelectric transport phenomena in three materials systems. The intrinsic thermoelectric properties of bismuth antimony telluride nanostructures, which are synthesized by two different methods, are characterized with a four-probe thermoelectric measurement method based on a suspended device. The obtained thermoelectric property reveals a transition from n-type to p-type electronic transport as the antimony to bismuth ratio is increased to about 0.25. The peak zT was found when this ratio is close to 0.5. A new four-probe thermal transport measurement method is established in this work to probe both the contact thermal resistance and intrinsic thermal resistance of a nanostructure, which can be either an electrical conductor or insulator. The effectiveness of this method is demonstrated with its use to reveal size-dependent thermal conductivity of patterned silicon nanowires. The new four-probe measurement method is employed to obtain both the intrinsic thermal and thermoelectric properties of nanostructures of boron arsenide (BAs) with potentially record high thermal conductivity. The measurement results suggest that the thermal conductivity of one of such sample with an equivalent diameter of about 1.1 μm is higher than that of bulk silicon, despite pronounced phonon scattering by surface roughness and point defects associated with arsenic vacancies. In addition, high thermoelectric power factor was measured on the BAs sample.