Thermoelectric Properties of Self-Assembled Nanocristals in Semiconductor Matrix: Experiment and Theory

本项目的目标是继续对无缺陷纳米晶(量子点，量子点)多层膜的热电性质进行实验和理论研究。研究将扩展到量子柱(QPS)，即相干嵌入SiGe(InGaAs)的短纳米线。在目前的资助期内，我们的实验表明，有可能将Ge/Si多层膜的热导率精确控制到低至1W/mK。此外，我们从理论上预测，通过对量子点多层膜的性质进行适当的设计，可以提高功率因数的值。然而，对跨平面热电势和电导率的实验测量仍然很少。因此，我们将通过改变相关的结构参数，如层间距和掺杂水平，来研究量子点和量子点的跨平面热电性质。结果将与使用原子模型获得的电子结构的真实描述的计算进行比较，并对超出恒弛豫速率近似的热电输运进行处理。此外，还将发展处理电子和声子系统中综合非平衡效应的理论方法。这两种材料体系之间以及量子点和量子点之间的比较有望为理解纳米结构半导体的热电性质提供重大进展。

Goal of this project is the continuation of the experimental and theoretical investigation of the thermoelectric properties of multilayers of defect-free nanocrystals (quantum dots, QDs) made of SiGe (InGaAs) in Si (GaAs) matrix. The investigations will be extended to quantum posts (QPs), i.e. short nanowires coherently embedded in SiGe (InGaAs). During the current funding period we have shown experimentally that it is possible to precisely control the thermal conductivity of Ge/Si multilayers down to values as low as 1 W/m.K. In addition, we have theoretically predicted that by proper engineering of the properties of QD multilayers, increased values of power factor can be expected. However, experimental measurements of cross-plane thermopower and electric conductivity are still scarce. We will therefore study cross-plane thermoelectric properties of QDs and QPs by varying relevant structural parameters, such as interlayer spacing, and doping level. The results will be compared to calculations using a realistic description of the electronic structure obtained from atomistic modelling and a treatment of thermoelectric transport beyond the constant-relaxation-rate approximation. Moreover, theoretical methods for treating combined non-equilibrium effects in both the electron and phonon system will be developed. The comparison between the two material systems and between QDs and QPs is expected to provide a significant advance on the understanding of the thermoelectric properties of nanostructured semiconductors.