硅锗基声子热电薄膜中的声子和电子输运特性研究

Thermoelectric devices show great application potentials in many areas, such as direct thermal energy conversion, thermal detection, waste heat recovery and chip cooling. However, currently the wide applications of thermoelectrics have been being limited by the low efficiency, high material cost and toxicity of thermoelectric materials. It is highly desirable to develop cost-effective, high-performance and environmentally-friendly thermoelectrics . High-performance thermoelectric materials require a low thermal conductivity but a high power factor, which are difficult to achieve in bulk materials due to the strong coupling between electron and phonon transports. Low-dimensional structures can achieve both but they are too expensive and very difficult to be integrated for large-scale applications. The proposed project aims to nanoengineer silicon, which is unsuitable for thermoelectric applications due to its high thermal conductivity, as an efficient thermoelectric material by introducing in-situ grown phononic nanodot array into silicon lattice to form Si-based nanocomposite. Through quantum or classical size effects and interface scattering, the transports of electron and phonon in this novel phononic nanocomposite can be decoupled and optimized individually. High-performance silicon-based nanocomposites will be ideal for thermoelectric applications because of their excellent scalability, low toxicity, and low cost. We plan to develop a scalable approach to fabricate "defect-free" silicon-based nanocomposites and study the various parameters that may affect their thermoelectric performance for further optimization. Furthermore, we will combine experimental investigations with theoretical analysis and simulations to explore the phonon transport and multi-interface scattering processes in these novel phononic metamaterials. This clarification will deepen the fundamental understanding of phonon behavior in nanostructured materials and enhance the development of novel high-performance thermoelectrics, which is of both academic and industrial importance.

热电器件在热能转换、热传感和电子芯片冷却等诸多领域有巨大应用潜力。 但目前热电系统的应用受限于热电材料的低效率、高成本和低环保性，迫切需要发展一种高效廉价的环保热电材料。高效热电材料要求低热导率和高功率因子，这在体材料中由于电子声子的强耦合难以同时实现，而低维材料造价高昂，难以集成应用。本课题拟通过在硅中引入原位生长的声子纳米点阵形成纳米复合物，通过尺寸效应和界面散射解耦电子和声子传输，将本不适于热电应用的硅改造成高效热电材料, 其低毒性，低成本和可伸缩性将有希望成为热电应用的理想候选。本课题将发展一种生成"无缺陷"硅基声子纳米复合物的方法，并对影响复合物热电属性的因素进行研究和优化。同时本课题将结合实验测量和理论分析模拟，对声子纳米复合结构中的声子输运和多界面散射过程进行研究。这将加深我们对声子微观尺度传输机理的认识，推动高效热电材料的发展, 对学术研究和工业应用都具有积极意义。

热电器件在热能转换、热传感和电子芯片冷却等诸多领域有巨大应用潜力。 但传统热电材料的低强度、高成本和低环保性限制了热电系统的应用，硅基热电材料由于其低成本,低毒性和与电子工艺高兼容性受到广泛重视。目前的硅基材料热导率较高从而导致热电性能较低，而同时实现低热导率和高功率因子在体材料中由于电子和声子的强耦合难以同时实现，而低维材料造价高昂，难以集成应用。如能在硅基材料中引入声子纳米结构形成纳米复合物，通过尺寸效应和界面散射解耦电子和声子传输，从而可以大幅提升硅基材料的热电性能。然而在本项目开展之前，文献中尚欠缺对硅基纳米复合薄膜的系统研究，也无高性能硅基热电薄膜的报导。本项目从实验加工合成与表征以及理论分析模拟两方面结合，对影响复合物热电属性的因素，诸如纳米结构的尺寸，排列和晶格匹配等进行研究和优化，揭示在硅基纳米复合材料中的声子与电子传输机制。在此基础上我们采用气相沉积法发展了具有天然柱状纳米结晶的n型和p型硅锗纳米复合薄膜，其室温热电性能分别达到0.16和0.2，是目前为止硅基薄膜材料的最高性能，并高出硅锗体材料最好性能近一倍。基于该薄膜,我们开发了尺寸小于1毫米的高性能悬空结构的平面型薄膜微型热电制冷器，所发展的单级制冷器可在室温下实现6毫秒的响应速度以及10.3 °C的冷却温度，为目前为止硅基微型热电制冷器的最高纪录，同时其冷却温度和能耗比值高达 184 °C /W。这表明本项目所发展的高性能纳米复合硅锗热电薄膜在集成式热电薄膜器件方面有很大的应用前景。在本项目期间，本项目组在国际知名杂志共发表SCI期刊论文12篇，其中Nano Letters (IF 12.712)1篇，Nanoscale (IF 7.367) 1篇，Applied Energy (IF 7.182)1篇，Carbon (IF 6.337)1篇，Journal of Physical Chemistry C(IF 4.536)2篇，Scientific Reports (IF 4.259) 3篇，Physical Review B (IF 3.718) 1篇，Applied Physics Letters (IF 3.411)1篇，International Journal of Heat and Mass Transfer (IF 3.458)1篇。截至目前，这12篇论文共有196次引用。