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硅衬底上嵌入二氧化硅中的3C-碳化硅量子点的制造变得简单而经济。然而，与预期相反，这些量子点还没有表现出电子或光致发光。假设与SiO_2中的Si纳米颗粒的情况类似，这是由SiC/SiO_2界面缺陷引起的，它允许载流子对的非辐射复合。本项目的目标是探索这种特殊的碳化硅/二氧化硅界面的结构，并使用原子分辨的模拟方法来识别抑制该系统发光的缺陷。为了实现这一点，将检查界面点缺陷的形成热及其电子结构。由于量子点的大小在几纳米的范围内，使用从头算方法直接模拟是不可能的。最近，利用基于密度泛函的紧束缚方法将量子力学处理过的团簇嵌入到分子力学模拟的固态环境中的研究取得了进展。它们允许从量子力学的角度检查界面缺陷，同时考虑了量子点和基质的影响。利用这种新的方法，可以建立嵌入量子点及其可能存在的界面缺陷的模型。在此基础上，应评估识别发光抑制界面缺陷的方法的适用性，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.