半导体纳米团簇中动力学过程的理论研究

The effects of lattice vibrations on the quantum states and optical properties in semiconductor nanoclusters are the key points for the manufacture of semiconductor quantum devices. The continuum model, which has been widely used to study the effects of lattice vibrations on the quantum states in nanoclusters, is deeply dependent on the accuracy of the empirical parameters. Comparing to the empirical models, the calculation of dynamical processes based on first-principles is currently limited to nanoclusters containing tens to hundreds of atoms, which are too small in experiments. In this project, the post-processes are combined with first-principle calculations to study the dynamical processes in semiconductor nanoclusters. With the single particle electronic and vibrational eigenstates obtained from first-principle calculations, the exciton states and the electron-phonon coupling matrix elements are calculated using configuration interaction and frozen-phonon approaches, respectively. Based on these results, the phonon-induced dephasing of excitons in semiconductor nanoclusters with diameter as 2-5 nm and the effects of lattice vibrations on the luminescence spectrum in semiconductor nanoclustes with diameter as 2-3 nm will be studied. The achievement of this project will provide a useful theoretical approach to study the dynamical process in semiconductor nanostructures and reveal the effects of lattice vibrations on the dephasing of quantum states and the luminescence spectrum in semiconductor nanoclusters. This project will give a theoretical guidance for the development of semiconductor quantum devices.

晶格振动对半导体纳米团簇量子态及光学性质的影响是研发半导体纳米器件所必须考虑的关键因素。传统的连续介质模型方法通过经验参数描述晶格振动对半导体纳米团簇量子态的影响，其结果严重依赖于所选用的参数。而现有的第一原理方法只能精确地研究由几十到上百个原子组成的小尺寸纳米团簇的动力学过程，难以与实验相比较。本项目将第一原理与后续计算方法相结合，通过第一原理计算得到半导体纳米团簇单电子态及晶格振动态，并应用组态相互作用及冻结声子算法计算半导体纳米团簇的激子态及激子-声子相互作用矩阵元。在此基础上研究直径为2-5纳米的半导体纳米团簇中由晶格振动导致的基态与激子态之间相干跃迁的失相现象，并研究直径为2-3纳米的半导体纳米团簇中晶格振动对发射光谱的影响。本项目的顺利实施将为研究半导体纳米团簇量子态动力学过程提供新的理论方法，揭示晶格振动对量子态失相及自发辐射的影响，并为半导体纳米器件的设计提供理论依据。

晶格振动对半导体低维纳米体系电子能态结构及光学性质的影响是半导体物理学的一个重要研究领域。但是，无论传统的连续介质模型方法或目前标准的第一原理计算方法都无法精确地计算出具有实际尺寸的半导体纳米体系中晶格振动对载流子超快动力学过程的影响及对电子能态结构的修正。本研究项目基于第一原理与后续计算相结合发展了一套研究晶格振动及电子-空穴之间相互作用对半导体低维纳米体系中载流子动力学过程及电子能带结构影响的理论方法。应用这一方法，本项目组系统地研究了III-V族，II-VI族，硅锗半导体纳米团簇及纳米金刚石体系中激子态及激子-声子耦合作用对激子态超快动力学过程的影响及对能带结构的修正作用，并与实验结果相比较。此外，在本项目的资助下还开展了晶格振动及电子-空穴间库仑相互作用对二维层状材料激子态超快动力学过程的影响以及纳米金刚石材料表面态领域的研究工作。本项目研究成果不仅进一步揭示了低维半导体纳米体系中电子-电子、电子-声子之间多体相互作用对载流子超快动力学过程及能带结构的修正作用，同时也为半导体量子器件的设计提供了相应的理论支持。