Zhou Zihang, Li Jiayi, Jia Mengjiang, Wang Hai, Huang Wenqi, Zheng Jun
School of Applied Science, Beijing Information Science and Technology University, Beijing 102206, China.
Key Laboratory of Optoelectronic Materials and Devices, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China.
Molecules. 2025 Apr 23;30(9):1875. doi: 10.3390/molecules30091875.
GeSn alloys are among the most promising materials for the fabrication of high-efficiency silicon-based light sources. However, due to the tendency of Sn to segregate to the surface during growth, it is challenging to achieve a high Sn concentration while maintaining high-quality GeSn alloys. Both theoretical and experimental studies have confirmed that non-substitutional Sn defects (VSnV) are the primary driving factors in Sn surface segregation. However, there is a discrepancy between existing theoretical and experimental findings regarding the variation in VSnV concentration with total Sn concentration. To clarify this issue, we first prepared GeSn materials with varying Sn concentrations using molecular beam epitaxy (MBE) and subjected them to annealing at different temperatures. Subsequently, we characterized the VSnV concentration and Sn surface segregation. The results indicate that a higher total Sn concentration and temperature lead to an increased VSnV concentration, and the proportion of VSnV relative to the total Sn concentration also increases, which is consistent with existing theoretical research. To explain these phenomena, we employed first-principles calculations based on density functional theory (DFT) to investigate the effect of varying the total Sn concentration on the formation of substitutional Sn (Sn) and VSnV in GeSn alloys, while simultaneously studying the migration kinetics of Sn atoms. The results demonstrate that as the total Sn concentration increases, the formation of Sn becomes more difficult, while the formation of VSnV becomes easier, and Sn atoms exhibit enhanced migration tendencies. The analysis of binding energies and charge density distribution maps reveals that this is due to the weakening of Ge-Sn bond strength with increasing Sn concentration, whereas the binding strength of VSnV exhibits the opposite trend. These findings demonstrate excellent agreement with experimental observations. This study provides both theoretical and experimental references for GeSn material growth and VSnV defect control through a combined theoretical-experimental approach, offering significant guidance for enhancing device performance.
锗锡合金是制备高效硅基光源最具潜力的材料之一。然而，由于锡在生长过程中有偏析到表面的倾向，在保持高质量锗锡合金的同时实现高锡浓度具有挑战性。理论和实验研究均证实，非替代型锡缺陷（VSnV）是锡表面偏析的主要驱动因素。然而，关于VSnV浓度随总锡浓度的变化，现有理论和实验结果存在差异。为了阐明这个问题，我们首先使用分子束外延（MBE）制备了不同锡浓度的锗锡材料，并在不同温度下对其进行退火。随后，我们对VSnV浓度和锡表面偏析进行了表征。结果表明，总锡浓度和温度越高，VSnV浓度越高，且VSnV相对于总锡浓度的比例也增加，这与现有理论研究一致。为了解释这些现象，我们基于密度泛函理论（DFT）进行了第一性原理计算，以研究总锡浓度变化对锗锡合金中替代型锡（Sn）和VSnV形成的影响，同时研究锡原子的迁移动力学。结果表明，随着总锡浓度的增加，Sn的形成变得更加困难，而VSnV的形成变得更容易，并且锡原子表现出增强的迁移倾向。结合能和电荷密度分布图的分析表明，这是由于随着锡浓度的增加，Ge-Sn键强度减弱，而VSnV的结合强度呈现相反的趋势。这些发现与实验观察结果高度吻合。本研究通过理论与实验相结合的方法，为锗锡材料生长和VSnV缺陷控制提供了理论和实验参考，为提高器件性能提供了重要指导。
