Department of Physics, Virginia Commonwealth University, Richmond, VA 23284, USA.
Nanoscale Res Lett. 2011 Aug 19;6(1):502. doi: 10.1186/1556-276X-6-502.
It is widely accepted that low dimensionality of semiconductor heterostructures and nanostructures can significantly improve their thermoelectric efficiency. However, what is less well understood is the precise role of electronic and lattice transport coefficients in the improvement. We differentiate and analyze the electronic and lattice contributions to the enhancement by using a nearly parameter-free theory of the thermoelectric properties of semiconductor nanowires. By combining molecular dynamics, density functional theory, and Boltzmann transport theory methods, we provide a complete picture for the competing factors of thermoelectric figure of merit. As an example, we study the thermoelectric properties of ZnO and Si nanowires. We find that the figure of merit can be increased as much as 30 times in 8-Å-diameter ZnO nanowires and 20 times in 12-Å-diameter Si nanowires, compared with the bulk. Decoupling of thermoelectric contributions reveals that the reduction of lattice thermal conductivity is the predominant factor in the improvement of thermoelectric properties in nanowires. While the lattice contribution to the efficiency enhancement consistently becomes larger with decreasing size of nanowires, the electronic contribution is relatively small in ZnO and disadvantageous in Si.
人们普遍认为，半导体异质结构和纳米结构的低维性可以显著提高其热电效率。然而，电子和晶格输运系数在提高中的精确作用还不太清楚。我们使用半导体纳米线热电性质的近无参数理论来区分和分析电子和晶格对增强的贡献。通过结合分子动力学、密度泛函理论和玻尔兹曼输运理论方法，我们为热电优值的竞争因素提供了一个完整的图景。例如，我们研究了 ZnO 和 Si 纳米线的热电性质。我们发现，与体材料相比，8 Å 直径的 ZnO 纳米线的优值可以提高 30 倍，12 Å 直径的 Si 纳米线的优值可以提高 20 倍。热电贡献的解耦表明，晶格热导率的降低是纳米线中热电性能提高的主要因素。虽然晶格对效率增强的贡献随着纳米线尺寸的减小而持续增大，但在 ZnO 中电子贡献相对较小，在 Si 中则不利。
