Modeling study of thermoelectric SiGe nanocomposites
Modeling study of thermoelectric SiGe nanocomposites
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DOI：
10.1103/physrevb.80.155327
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发表时间：
2009-10-01
影响因子：
3.7
通讯作者：
Vashaee, D.
中科院分区：
文献类型：
--
作者：
Minnich, A. J.;Lee, H.;Vashaee, D.
纳米复合热电材料由于其热电性能优于相应的块体材料而引起了人们的广泛关注。为了更好地理解所报道的数据并深入了解纳米复合材料中的输运，我们使用弛豫时间近似下的Boltzmann输运方程来计算n型和p型SiGe纳米复合材料的热电性质。我们占强晶界散射机制，在纳米复合材料中使用声子和电子晶界散射模型。该分析的结果与最近报道的n型纳米复合材料的测量结果非常一致，但p型纳米复合材料的实验Seebeck系数比模型预测值高出约25%。造成这种差异的原因目前尚不清楚，需要进一步调查。使用新的迁移率测量和模型，我们发现，掺杂剂沉淀是一个重要的过程中，在n型和p型纳米复合材料，在体硅锗，掺杂剂沉淀是最显着的，只有在n型材料。该模型还表明，解释数据所需的晶界处的势垒比使用泊松方程估计的值大几倍，表明材料中存在晶体缺陷。这表明，通过减少缺陷的数量或减少晶界处的俘获态的数量，可以提高迁移率。
Nanocomposite thermoelectric materials have attracted much attention recently due to experimental demonstrations of improved thermoelectric properties over those of the corresponding bulk material. In order to better understand the reported data and to gain insight into transport in nanocomposites, we use the Boltzmann transport equation under the relaxation-time approximation to calculate the thermoelectric properties of n-type and p-type SiGe nanocomposites. We account for the strong grain-boundary scattering mechanism in nanocomposites using phonon and electron grain-boundary scattering models. The results from this analysis are in excellent agreement with recently reported measurements for the n-type nanocomposite but the experimental Seebeck coefficient for the p-type nanocomposite is approximately 25% higher than the model's prediction. The reason for this discrepancy is not clear at the present time and warrants further investigation. Using new mobility measurements and the model, we find that dopant precipitation is an important process in both n-type and p-type nanocomposites, in contrast to bulk SiGe, where dopant precipitation is most significant only in n-type materials. The model also shows that the potential barrier at the grain boundary required to explain the data is several times larger than the value estimated using the Poisson equation, indicating the presence of crystal defects in the material. This suggests that an improvement in mobility is possible by reducing the number of defects or reducing the number of trapping states at the grain boundaries.