This study presents the material design of Si1−xGex epitaxial films/Si for thin film thermoelectric generators (TFTEGs) by investigating their thermoelectric properties. The thermoelectric films composed of group-IV elements are advantageous due to their compatibility with the Si process. We fabricated Si1−xGex epitaxial films with various controlled x values and strains using various growth methods. Ge epitaxial films without strains exhibited the highest thermoelectric power factor (∼47 μW cm−1 K−2) among various strain-controlled Si1−xGex (x ≠ 1) epitaxial films, which is higher at room temperature than SiGe alloy-based bulks ever reported. On the other hand, strained Si1−xGex epitaxial films showed an ultralow thermal conductivity of ∼2 W m−1 K−1, which is close to the value for amorphous Si. In addition to strained SiGe films with the ultralow thermal conductivity, unstrained Ge films with a high thermoelectric power factor can also be used for future TFTEGs by applying a nanostructuring technique. A preliminary TFTEG of Ge epitaxial films was realized, which generated a maximum power of ∼0.10 μW cm−2 under a temperature difference of 20 K. This demonstrates that epitaxial films composed of group-IV semiconductors are promising materials for TFTEG applications.

中文翻译：

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Si(001) 上的热电 Si1-xGex 和 Ge 外延膜，具有可控的成分和应变，用于基于 IV 族元素的热电发电机

本研究通过研究薄膜热电发生器 (TFTEG) 的热电性能，介绍了 Si1-xGex 外延膜/Si 的材料设计。由 IV 族元素组成的热电膜因其与 Si 工艺的兼容性而具有优势。我们使用各种生长方法制造了具有各种受控 x 值和应变的 Si1-xGex 外延膜。在各种应变控制的 Si1-xGex (x ≠ 1) 外延膜中，无应变的 Ge 外延膜表现出最高的热电功率因数 (∼47 μW cm-1 K-2)，在室温下比基于 SiGe 合金的块体更高曾经报道过。另一方面，应变 Si1-xGex 外延膜表现出 ∼2 W m-1 K-1 的超低热导率，接近非晶硅的值。除了具有超低热导率的应变 SiGe 薄膜外，通过应用纳米结构技术，具有高热电功率因数的非应变 Ge 薄膜也可用于未来的 TFTEG。实现了 Ge 外延膜的初步 TFTEG，在 20 K 的温差下产生了约 0.10 μW cm-2 的最大功率。这表明由 IV 族半导体组成的外延膜是用于 TFTEG 应用的有前途的材料。