Understanding the Luminescence Efficiency of Silicon Quantum Dots

迄今为止，硅量子点的光学性质中有很大一部分仍处于争论中，或完全未知，或超出了实验范围。该合作项目旨在澄清几个重要的性质，这些性质需要全面了解零维硅纳米结构的物理机制和光学性能的限制。这项研究的动机有两个方面：一方面，基础半导体科学将从对间接量子点（如硅）的尺寸效应的全面理解中受益，当尺寸减小到激子玻尔半径以下时，就会发生这种效应。然而，除了这种合理的学术兴趣之外，硅代表了技术上最重要和几乎无处不在的半导体。微电子工业的积极缩小正在逐步减少活性硅的体积到量子限制效应开始发挥主要作用的尺寸范围。因此，广泛的知识是必需的，包括这些相邻量子点的串扰。据报道，对于独立的Si量子点，Si量子点的发光效率很容易达到25%，甚至达到50%。与10-5的体硅量子产率相比，尺寸减小到5nm为全新的应用领域打开了一扇大门。目前，硅光电子技术能够修改、引导、开关和探测光，但它不能有效地从电力中产生光。然而，光电子学中的光源通常由III-V半导体制成，这些半导体在材料层面上无法集成到微电子电路中（Si是许多III-V材料的掺杂剂，这些材料大多是Si的中隙缺陷态）。实际上，要想完全用硅基材料制造光片上通信，还有很长的路要走。但可以理所当然地认为，硅纳米结构将是这项技术发展的关键点。因此，深入研究硅量子点的基本光学特性和光学性能的主要极限是非常重要的。本文将详细研究以下目标：(1)Si量子点的吸收截面（ACS）， (2) Si量子点的量子产率，以及(3)介电矩阵与Si量子点的相互作用。

Significant part of the optical properties of Si QDs is either still under controversial debate or completely unknown or was out of experimental reach up to now. This cooperation project aims to clarify several important properties that are required to obtain a comprehensive picture of the physical mechanisms and limits of the optical performance of 0 dimensional silicon nanostructures. The motivation for this study is two-fold: On the one hand, fundamental semiconductor science will benefit in general from a comprehensive understanding of the size effects in indirect quantum dots such as Silicon that occur when the dimensions are reduced below the exciton Bohr radius. However, apart from this well justified academic interest, silicon represents the technologically most important and virtually omnipresent semiconductor. The aggressive down-scaling of microelectronics industry is progressively reducing the active silicon volumes into a size range where quantum confinement effects start to play a major role. Hence, extensive knowledge is mandatory including the cross-talking of such adjacent quantum dots. For free standing Si QDs the light emission efficiency of Si QDs can easily reach 25% and even ~50% were reported. Compared to the bulk Si quantum yield of 10-5 the reduction of the dimensions to 5 nm opens a gate into a completely new world of applications. Currently, silicon optoelectronics is able to modify, guide, switch and detect light but it is not able to efficiently generate light from electricity. However, the light sources in optoelectronics are often made of III-V semiconductors which cannot be integrated on the material level into microelectronic circuits (Si is a dopant for many III-V materials and those are mostly mid-gap defect states in Si). Realistically, there is still a long way to go until e.g. optical on-chip communication can be solely fabricated from Si-based materials. But it can be taken for granted that Si nanostructures will be the pivotal point of this technology evolution. Therefore, intense research on fundamental optical properties and the principal limits of the optical performance of Si quantum dots is important. In detail the following objectives will be investigated in details: (1) Absorption Cross Section (ACS) of Si QDs, (2) Quantum Yield of Si QDs, and (3) Interaction of the Dielectric Matrix with Si QDs.