Phosphorous und Boron in nanoscale Silicon - Investigation of Doping and Defect Mechanisms

硅的电学性质可以通过掺杂磷和硼来控制，它是电子、光电子和光伏等多种技术应用的基础。尤其是cmos晶体管技术接近了出现量子限制效应的尺寸的阈值。在纳米尺度上，半导体的各种问题--物理、热力学或统计性质--阻碍了场效应晶体管的源区/漏区的成功和可靠的掺杂，这似乎阻碍了进一步的小型化。另一方面，各种文献报道了几个纳米尺寸的硅量子点的P掺杂和B掺杂的成功。我们最近对5 nm硅量子点的P掺杂的研究重复了文献报道。然而，结合详细的结构测量和统计分析(原子探针断层扫描，基于同步辐射的x-way吸收光谱)，人们怀疑，光学和电学测量的硅量子点性质的变化是否真的是由P掺杂引起的。我们的数据显示，每个量子点有相当多的P原子，尽管似乎只有百分比的部分被电离，电离能是体硅的2-3倍。用密度泛函方法对P掺杂的Si近似物进行了模拟，结果表明，对于所有可能的构型，都没有提供大多数载流子的态。然而，在带边附近出现了各种状态，这些状态代表了可能的缺陷和复合中心。这些态似乎是光致发光衰减和电导改善的一个可行的解释。在这项初步工作的基础上，我们想要在这个方案中详细研究纳米硅的P掺杂和B掺杂。主要目标是阐明各种文献报告之间的矛盾，以及建立对缺陷和兴奋剂机制的全面概述。为此，我们拥有一套经过数年优化的样品系统，以及大量经过认可的结构、光学和电学测量仪器。考虑到未来硅基电子学的重要性，研究纳米级硅的掺杂是当务之急。本项目提案的实验和人员配置提供了实现关键研究结果的理想机会，这些结果揭示了在未来场效应管的生成中可以在多大程度上使用经典掺杂，以及必须预期什么样的缺陷机制。

Silicon, whose electronic properties can be controlled via doping with phosphorous and boron, is the basis of manifold technological applications in electronics, optoelectronics, and photovoltaics. Especially the CMOS transistor technology approaches the threshold to dimensions where quantum confinement effects occur. On the nanoscale various problems of semiconductor-physical, thermodynamical, or statistical nature impede the successful and reliable doping of source/drain regions of field effect transistors which appear to prevent further miniaturization. On the other hand, various papers report on successful P- and B-doping of silicon quantum dots (Si QDs) of few nanometers in size. Our recent studies on P-doping of 5 nm Si QDs reproduce the literature reports. However, the combination with detailed structural measurements and statistical analysis (atom probe tomography, synchrotron-based x-way absorption spectroscopy) created doubt, whether the optically and electrically measured changes of the Si QD properties are indeed caused by real P-doping. Our data reveals a rather large number of P-atoms per QD, though only a percent fraction seems to be ionised with 2-3 times higher ionisation energies than for bulk-Si. Density functional simulations of P-doped Si approximants reveal no states providing majority carriers for none of the potential configurations. Various states in the vicinity of the band edges occur, however, which represent possible defect- and recombination centers. These states seem to be a feasible explanation for the attenuated photoluminescence and the improved conductance. Based on this preliminary work we want to investigate within this proposal the P- and B-doping of nanoscale silicon in detail. The major goal is the elucidation of the contradiction between the various literature reports as well as the creation of a comprehensive overview of defect- and doping mechanisms. For this endeavour we possess a sample system which was optimized for several years as well as an extensive tool box of approved structural, optical, and electrical measurement instruments.Considering the importance of future Si-based electronics, the investigation of doping of nanoscale silicon is of utmost priority. The experimental and personnel configuration of this project proposal offers the ideal chance to achieve crucial research results that reveal to which extent classical doping can be employed in future field effect transistor generations and what kind of defect mechanisms have to be expected.