Identification of luminance-suppressing interface defects at SiC quantum dots embedded in SiO2, using multiscale QM/MM simulations

一种新的实验方法使得在Si衬底上嵌入SiO2的3C-SiC量子点的制造变得简单而经济。然而，与预期相反，这些量子点尚未表现出电致发光或光致发光。假设与SiO2中Si纳米颗粒的情况类似，这是由SiC/SiO2界面缺陷引起的，该缺陷允许载流子对的非辐射重组。本项目的目标是探索这种特定的SiC/SiO2界面的结构，并利用原子分辨模拟方法确定该系统中抑制发光的缺陷。为了实现这一目标，将对界面点缺陷及其电子结构的形成焓进行研究。由于量子点的尺寸在几纳米范围内，使用ab-initio方法直接模拟是不可能的。最近，使用基于密度泛函的紧密结合方法将量子力学处理的团簇嵌入到由分子力学模拟的固态环境中取得了进展。考虑到量子点和矩阵的影响，它们可以用量子力学的方法检查界面缺陷。利用这种新方法，可以构建具有可能存在的界面缺陷的嵌入式量子点模型。在此基础上，评估该方法识别抑制发光界面缺陷的适用性，并开始寻找此类缺陷。

A new experimental method allows easy and cost-effective manufacture of 3C-SiC quantum dots embedded in SiO2 on a Si substrate. However, contrary to expectations, these QD do not yet exhibit electro- or photoluminiescence. It is assumed that, similar to the situation with Si nanoparticles in SiO2, this is caused by SiC/SiO2 interface defects, which allow non-radiative recombination of carrier pairs. The goal of this project is to explore the structure of this specific SiC/SiO2 interface and to identify the defects which suppress luminescence in this system, using atomically resolved simulation methods. To achieve this, formation enthalpies of the interface point-defects and their electronic structures will be examined. A direct simulation using ab-initio methods is impossible since the size of the quantum dots is in the range of several nm. Recently, advances in the embedding of quantum mechanically treated clusters, using the density-functional based tight-binding method, into solid state surroundings modeled by molecular mechanics, were achieved. They allow to examine interface defects quantum mechanically, taking into account influences from the quantum dot and the matrix. Using this new method, models of embedded quantum dots with their possible interface defects shall be constructed. Based on this, the suitability of the method to identify luminescence suppressing interface defects shall be evaluated and the search for such defects begun.