锗/锗-锡核壳纳米线形貌形成及成分分布的机理研究

锗锡合金，因其能带结构受锡成分的可调性以及与主流硅基元件的相容性，被认为是一种在光电领域极具前景的新型半导体材料。锗/锗-锡核壳纳米线是以异质外延生长方式合成锗锡合金的有效思路。其优势不仅在于引入了应变工程与载流子约束效应，更在于其可实现锡在锗中的过饱和掺入，带来材料向直接带隙转变的可能性。然而在实际生长过程中，尚存在无法完全理解控制的纳米线反常形貌与成分分布不均等问题，这成为该材料可控合成与应用开发的瓶颈。本课题拟通过构建先进的多场耦合相场模型，描述核壳纳米线生长过程中界面能、驱动力、成分与应变之间的内在联系；通过联合分子动力学方法，建立具完备性的多尺度模拟框架，从而研究材料本征性质与形貌结构对生长行为的共同作用；通过捕捉纳米线生长动态及自由能演化过程，创建对决定纳米线形貌形成与成分分布关键因素与临界条件的定量预测方法，最终为核壳纳米线及类似异质结构的合成设计与优化提供科学依据与指导。

Ge1-xSnx alloys are considered a promising new semiconductor material for optoelectronic applications, due to its band structure tunability by Sn composition and compatibility with the mainstream Si-based devices. Ge/Ge1-xSnx core-shell nanowires offer a plausible solution for achieving low-dimensional hetero-epitaxial Ge1-xSnx growth, whose merits include not only the introduction of strain-engineering and carrier confinement effect, but also the realization of supersaturated incorporation of Sn in Ge, that leads to the transition from an indirect band-gap to a direct band-gap. However, in the process of nanowire growth, abnormal nanowire morphologies and inhomogeneous Sn distributions have often been observed, and have yet to be fully understood. This becomes the bottleneck of controllable synthesis of the material toward its further development and application. This project aims to develop an advanced multi-field coupled phase-field model, in order to describe the underlying connections among interfacial energies, chemical potentials, Sn compositions and strain distributions during the growth of Ge/Ge1-xSnx core-shell nanowires. By combining molecular dynamics models, a self-contained multi-scale modeling framework will be constructed, as an enabler of studying the joint effects of materials’ intrinsic properties and structural features on the nanowire growth behaviors. The phase field simulations will be able to capture the dynamical process of core-shell nanowire growth as well as the evolution of the free energy of the system, from which key factors and critical conditions can be quantitively predicted for determining the nanowire morphology and Sn composition. The outcomes of the proposed work should provide new understandings and scientific guidelines, for designing and optimizing synthesis pathways of Ge/Ge1-xSnx core-shell nanowires and similar heterogeneous nano-structures.