Experimental and theoretical investigations of the thermoelectric properties of isotropically modulated silicon multilayers

纳米结构半导体开启了通过操纵声子输运来独立调整电导率和导热率的机会。在第一个资助期内，我们通过时域测温表明，由（28Si/29Si）双层组成的同位素多层结构显示出来自顶层金属层的热流减少。初步计算证实不同同位素组成的硅层之间的电导率降低。我们建议充分利用这些结构的自由度，同时使用硅同位素30，构建非周期多层堆叠，并通过反应离子蚀刻引入侧向约束，以优化输运性质，并展示具有改进性能的原型器件。同位素调制硅多层代表了一个优秀的模型系统，它既可以通过实验获得热性质（时域方法，3ω），也可以进行详细的理论计算（分子动力学和从头算）。同时，使用硅作为热电材料是非常可取的。对于几乎所有的热电应用，原材料的成本和所需的加工技术是至关重要的。因此，我们使用同位素富集硅的方法可能为未来的商业产品铺平道路。

Nanostructured semiconductors open the opportunity to independently tailor electric and thermal conductivity by manipulation of phonon transport. Within the first funding period we have shown by means of time-domain thermometry that isotope multilayer structures consisting of bilayers of (28Si/29Si) show a reduction of heat flow from a top metal layer. Preliminary calculations confirm a reduced conductance between silicon layers of different isotopic composition. We propose to fully exploit degrees of freedom of these structures by using as well the silicon isotope 30, building aperiodic multilayer stacks and introducing lateral confinement by reactive ion etching for optimizing the transport properties and show prototypic devices with improved figure of merit. Isotopically modulated silicon multilayers represent an excellent model system, which allows both for accessing the thermal properties experimentally (time domain methods, 3ω) and performing detailed theoretical calculations (molecular dynamics as well as ab-initio calculations). At the same time the use of silicon as a thermoelectric material is highly desirable. For almost all thermoelectric applications, the costs of raw materials and the required processing technique is crucial. Thus our approach using isotopically enriched silicon might pave the way for future commercial products.