Theoretical Study On Thermoelectric Properties And Regulation Of Silicon Nanowires

Thermoelectric materials can directly convert waste heat into electrical energy,which is one of the effective ways to alleviate the energy shortage and environmental pollution problems faced by various countries.As a basic element of modern microelectronics and photovoltaic industry,silicon has the advantages of low cost,non-toxicity and rich content,and it plays an important role in the current high-tech field.However,the high inherent lattice thermal conductivity also greatly limits the wide application of silicon in thermoelectric fields.Therefore,how to effectively reduce the thermal transport properties of silicon materials is the focus of current scientific researchers.In this article,we use DFTB combined with NEGF to systematically explore the thermoelectric conversion properties of several typical silicon nanowires,and discuss the influence of morphology,crystal orientation,and core-shell structure on the thermoelectric properties of nanowires.The research results are expected to provide a reliable theoretical basis for the design and development of silicon-based nano-thermoelectric materials.The main research content of our article is distributed as follows:（1）We systematically studied the thermoelectric transport properties of Si₂₄nanowires with different crystal orientations,and the results show that Si₂₄nanowires along the[010]crystal orientation have excellent thermoelectric properties.Its ZT value reaches 1.28 at room temperature,which is 2.1 times that of diamond silicon nanowires.This is because Si₂₄NW-[010]exhibits excellent electron transport properties and lower phonon thermal conductivity.In order to improve the thermoelectric properties of nanowires,we systematically explored the influence of the core-shell structure on the thermoelectric properties of silicon nanowires.The research results show that the core-shell structure can greatly improve the thermoelectric quality factor of nanowires.By analyzing the power factor and phonon thermal conductivity of nanowires,we find that the decrease of phonon thermal conductivity plays a leading role in the increase of its ZT value.（2）We used DFTB combined with NEGF method to study the thermoelectric properties of d-Si NW-[111],Si₃₄NW and Si₄₆NW with extremely small diameters.Our calculation results show that Si₃₄NW and Si₄₆NW have excellent electron transport characteristics.At room temperature,the Seebeck coefficients of Si₃₄NW and Si₄₆NW reached 2.49 m V/k and 2.74 m V/k,respectively.In the study of the phonon transport properties of nanowires,we found that the phonon thermal conductivity of Si₃₄NW is the lowest.Based on the properties of electron transport and phonon transport,we have obtained the thermoelectric figure of merit ZT of d-Si NW-[111],Si₃₄NW,and Si₄₆NW.We found that the thermoelectric performance of Si₃₄NW is the best,reaching 1.5 at room temperature.