Calculation, measurement and control of the energy barriers and the light-induced kinetics of the A_Si-Si_i defect

硅基光电器件作为太阳能电池或探测器是我们日常生活的一部分，其在正常工作模式下由光或电荷载流子引起的逐渐退化具有重要的技术和经济意义。欧洲核子研究中心的硅基粒子物理辐射探测器提供了一个极端的例子。为了制定适当的策略来避免功能的丧失，必须了解光诱导的产生和降解缺陷的动力学。这个研究项目就是从这里开始的。研究了一种重要的、典型的光致缺陷——A_Si-Si_i缺陷。该缺陷由位于规则晶格位置的受体原子（例如，硼或铟）和位于相邻间隙位置的硅原子组成。在实验与理论的密切配合下，对这类缺陷要有一个全面的认识。目的是最终解决文献中基于实验数据提出的结构模型与理论推导模型之间存在的差异。此外，B_Si-Si_i缺陷是导致所谓硼氧光诱导降解（BO-LID）的工作假设也将得到验证。为此，必须对缺陷的结构和动力学进行实验分析，同时进行理论描述。例如，计算出的该缺陷两种状态之间的势垒高度应与三种不同实验方法的结果进行比较。这些是低温光致发光光谱，电子自旋共振光谱和微波检测光导衰减载流子寿命测量。为了以可控的方式控制缺陷，对各种硅样品进行了退火。为此，首先用尽可能高的缺陷密度制备样品，因此期望得到强信号。目标退火协议旨在实现缺陷密度的持续降低。从技术角度来看，这可以用来抵消辐射造成的效率损失问题。然而，本研究项目的主要目标是建立对A_Si-Si_i缺陷、其结构和动力学以及缺陷引起的载流子重组的基本和全面的微观认识和模型。

Silicon-based optoelectronic devices are part of our everyday life as solar cells or detectors and their gradual degradation induced by light or charge carriers in normal operation mode is therefore of technological and economic importance. The silicon-based particle physics radiation detectors at CERN provide a drastic example. In order to work out adequate strategies to avoid the loss of function, the light-induced generation and kinetics of the defects underlying the degradation have to be understood.This is where the research project starts. It investigates the A_Si-Si_i defect, an important and exemplary type of light-induced-defect. This defect consists of an acceptor atom (e.g., boron or indium) on a regular lattice site and a silicon atom on an adjacent interstitial site. In close cooperation of experiment and theory, a comprehensive understanding of this kind of defects shall be worked out. The aim is to finally resolve a discrepancy existing in the literature between structural models proposed on the basis of experimental data and theoretically derived models. Also, the working hypothesis that the B_Si-Si_i defect is the cause of the so-called boron-oxygen-light-induced degradation (BO-LID) will be checked. For this purpose, the structure and kinetics of the defect shall be analyzed experimentally and simultaneously described theoretically. For example, calculated barrier heights between two states of this defect shall be compared with the results of three different experimental methods. These are low-temperature photoluminescence spectroscopy, electron spin resonance spectroscopy, and microwave-detected photoconductivity decay for carrier lifetime measurement. Annealings of various silicon samples are carried out with the aim of controlling the defect in a controlled manner. For this purpose, the samples are first prepared with the highest possible defect density, and therefore strong signals are to be expected. Targeted anneal protocols aim to achieve a sustained reduction in defect density. From a technological perspective, this can be used to counteract the problem of loss of efficiency due to irradiation. The main goal of the research project, however, is to develop a fundamental and comprehensive microscopic understanding of and a model for the A_Si-Si_i defect, its structure and dynamics as well as the defect-induced recombination of charge carriers.