纳米多孔结构单晶硅热电薄膜声子热导率数值研究

摘要

为降低多孔热电薄膜的热导率来提升其热电转换效率,基于离散坐标法和松弛时间近似模型求解声子Boltzmann输运方程,对单晶硅纳米多孔热电薄膜声子热导率进行了数值研究,获得了多孔硅薄膜厚度、孔隙率、边界镜面率和声子散射边界面积对其热导率的影响规律,讨论了孔隙率、多孔薄膜厚度对薄膜各向异性导热特性的影响.结果表明:随着孔隙率的增加及薄膜厚度的减小,热导率逐渐降低;当孔隙率增加到64％,且硅薄膜厚度减小到块材料硅声子平均自由程的1/10时,与块材料热导率相比,薄膜热导率至少下降两个数量级.通过分析多孔薄膜中的热流分布特性,提出了优化设计薄膜多孔结构的方法,为设计低热导率高效热电薄膜提供了理论依据.%To reduce the thermal conductivity of porous thermoelectric thin film and improye the thermoelectric conversion efficiency,a solver of the phonon Boltzmann transport equation with the relaxation time approximation and discrete ordinates method is developed to numerically study the phonon thermal conductivity of the nanoporous silicon thin film.The effects of film thickness,film porosity,boundary specularity and phonon scattering boundary area on the thermal conductivity are researched.The effects of the porosity and film thickness on the anisotropic thermal conduction are also discussed.The results show that the thermal conductivity gets lower as the porosity increases and the film thickness decreases,and can be reduced at least by two orders of magnitude compared with the bulk silicon when the film porosity rises up to 64％ and the film thickness is less than 0.1 times of the phonon mean free path of the bulk silicon.According to the heat flux distribution in the nanoporous thin film,a method is proposed to optimize the porous structure of the nanoporous thin film,which may provide a theoretical guidance for the design of low-thermal conductivity and high-efficient thermoelectric thin films.