高能离子辐照诱导的硅锗合金热电性能演化机理研究

Radioisotope thermoelectric generator is the only power supply system on the deep space probes so far. Silicon-germanium (SiGe) alloy is preferred thermoelectric material for thermoelectric generator on space probes due to its remarkable high-temperature thermoelectric properties. However, the high-energy ions in space environment induce structural damages in the SiGe alloy and then result in the performance degradation of SiGe material and thermoelectric generator. In order to accurately evaluate the operating life of thermoelectric generator, it is imperative to study the thermoelectric performance evolution mechanism of silicon-germanium alloy induced by high-energy ion irradiation. In this project, P-type and N-type monocrystalline Si0.8Ge0.2 samples will be taken as the research objects, and a variety of analysis methods will be used to study the irradiation effects on the SiGe samples induced by high-energy Si and Ge ions delivered by HIRFL (Heavy Ion Research Facility in Lanzhou). The generation of defects, formation of microstructural damages and variation in the thermoelectric properties, such as electrical conductivity, thermal conductivity and Seebeck coefficient will be studied in this project. The relationship between thermoelectric performance and irradiation parameters will be established. As a result, the thermoelectric performance evolution mechanism of silicon-germanium alloy induced by high-energy ion irradiation will be explored.

对于深空探测器来说，放射性同位素温差发电器是目前唯一的供电系统。硅锗合金具有优良的高温热电性能，是深空探测器上温差发电器件的首选热电材料。然而，空间环境中的高能离子会在硅锗合金中引起结构损伤，进而导致材料热电性能的恶化和温差发电器件性能的衰退。为了准确地评估温差发电器件的运行寿命，高能离子辐照下硅锗合金热电性能的演化机理研究势在必行。本项目选择P型和N型单晶Si0.8Ge0.2合金为研究对象，利用兰州重离子加速器HIRFL提供的高能Si和Ge离子进行辐照，结合多种分析手段研究高能离子辐照在硅锗合金中引起的缺陷的产生和结构损伤的形成，以及由此导致的硅锗合金电导率、热导率和Seebeck系数等热电性能的变化，建立样品热电性能与辐照参数之间的联系，探索高能离子辐照下硅锗合金热电性能的演化机理。

硅锗合金具有优良的高温热电性能，因此被用作空间探测器上的温差发电器材料。近年来，有研究发现具有纳米结构的硅锗合金的热电性能要优于传统硅锗合金材料，有望替代传统硅锗合金作为新型高效的高温热电材料。因此，纳米结构化的硅锗合金的相关研究受到了人们的日益重视。同时，具有低维度纳米结构的硅锗超晶格薄膜由于具有更高的理论热电优值同样受到广泛关注。本项目以硅锗超晶格薄膜和硅锗合金材料为研究对象，其中超晶格薄膜利用磁控溅射法制备得到，研究了沉积参数对超晶格薄膜微观结构的影响。硅锗合金块体样品是以高纯硅粉和锗粉为原料，添加磷或硼作为导电相，通过高能球磨和放电等离子烧结的方式制备得到具有纳米结构的N型或P型硅锗合金，研究了导电相掺杂量和制备工艺对其微观结构及电导率、热导率和Seebeck系数等热电性能的影响。然后利用keV的He离子和MeV的Fe离子对硅锗合金进行了辐照，研究了入射离子种类、能损和剂量等辐照参数对硅锗合金微观结构的影响，分析了硅锗合金在入射离子作用下的微观结构损伤机制。