Dynamics of Local Vibrational Modes in Semiconductors

技术支持：本计画的目标是阐明半导体的局域振动模（LVMs）与声子池及电子能带结构的耦合。直接探测这些途径和速率的能力允许在新的精度水平上测试理论。嵌入半导体中的氢特别令人感兴趣，因为相关的LVMs可以被干净地激发，并且通常在能量上与声子浴很好地分离。由半导体中的氢同位素组成的材料系统可能会受到这种能量途径的性质的强烈影响，因为弛豫时间可以决定半导体/氢系统的稳定性。以前，我们研究了振动寿命的各种H，D和O相关的点缺陷在体硅和锗使用超快激光。这些研究表明，振动衰减率的异常变化为100倍。如此大的变化在固体中是不寻常的，并激发了更深入的理解。这些寿命测量给出了控制Si MOSFET可靠性值的基本参数的指示。这个项目的目的是探索大的结构依赖的动力学参数，并获得更好的理解本地模式，声子浴和电子系统之间的优先耦合。虽然与本征半导体的带隙相比，LVM的能量很小，但p型或n型半导体和激光诱导的自由载流子浓度都提供了能量可达的通道。电子通路的存在影响人口寿命和线宽，并可能占戏剧性的网站依赖性。这些替代的衰变通道将实验研究，通过将掺杂剂的结构，以及激光诱导的e-h激发本征材料，包括Si，Ge，GaX（X = As，N，P）和ZnO。非技术：该项目为研究生和本科生提供跨学科领域的综合教育和研究培训，包括现代光学，材料科学和计算建模。此外，理解皮秒时间尺度上的激发态寿命将描述物理学家，材料科学家，化学家和工程师感兴趣的晶体半导体中缺陷和杂质的振动动力学。该项目的一个重要目标是向更大的潜在感兴趣的研究人员社区展示这种方法的有效性。此外，在附近的托马斯杰斐逊实验室和威廉和玛丽学院的这项研究开发和支持的实验能力的组合将继续提供给国内和国际研究人员，利用该项目的影响。

Technical: The objective of this project is to elucidate the coupling of local vibrational modes (LVMs) of semiconductors to the phonon bath, and to the electronic band structure. The ability to directly probe these pathways and rates allows tests of theory at new levels of precision. Hydrogen embedded in semiconductors is of particular interest, since the associated LVMs can be excited cleanly, and are usually well separated in energy from the phonon bath. Materials systems consisting of hydrogen isotopes in semiconductors may be strongly influenced by the nature of this energy pathway, as the relaxation time can determine the stability of the semiconductor/hydrogen system. Previously, we studied vibrational lifetimes of various H, D and O related point defects in bulk Si and Ge using ultrafast lasers. These studies indicate extraordinary variations of a factor of 100 in vibrational decay rates. Such large variations are unusual in solids and motivated a deeper understanding. These lifetime measurements give an indication of fundamental parameters controlling Si MOSFET reliability values. The aim of this project is to explore the large structural dependence of dynamical parameters, and to obtain a better understanding of preferential coupling between local modes, the phonon bath, and the electronic system. Although the energy of the LVM is small compared to the band-gap of an intrinsic semiconductor, both p- or n-type semiconductors and laser-induced free-carrier concentrations provide energetically accessible channels. The existence of electronic pathways influences population lifetimes and linewidths and may account for the dramatic site dependence. These alternative decay channels will be studied experimentally by incorporating dopant structures as well as laser-induced e-h excitation in intrinsic materials, including Si, Ge, GaX (X = As, N, P) and ZnO. Non-Technical: This project provides integrated education and research training to graduate and undergraduate students in an interdisciplinary field including modern optics, materials science and computational modeling. Additionally, understanding excited state lifetimes on a picosecond timescale will delineate vibrational dynamics of defects and impurities in crystalline semiconductors of interest to physicists, materials scientists, chemists, and engineers. An important goal of the project is to demonstrate the efficacy of this method to a much larger community of potentially interested investigators. Also, the combination of experimental capabilities developed and supported by this research at the nearby Thomas Jefferson Laboratory and at the College of William and Mary will continue to be made available to domestic and international researchers, leveraging the impact of this project.