Dynamics of Local Vibrational Modes in Semiconductors

本研究计划的目的是阐明半导体中缺陷和杂质复合物的局域振动模式（LVMs）的动力学。研究重点是晶体半导体中的LVMs，包括质子和氘注入Si和Ge中含氢和氘复合物的拉伸模式，Si和GaAs中的受主和施主氢复合物，以及Si，Ge和GaAs中间隙O的反对称拉伸模式。第一激发振动能级的布居寿命和退相时间将使用瞬态漂白和光子回波测量来确定。时间分辨非线性光学研究将在托马斯杰斐逊国家加速器装置的自由电子激光器的短脉冲高功率可调谐红外辐射下进行。氢和氘相关的模式，其中有广泛不同的相互作用与晶体半导体中的体声子之间的比较，将有助于确定的弛豫机制。温度依赖性的研究将进行阐明本地模式和晶体的声子带之间的耦合机制。几个重要的问题将得到解决，关于振动能量弛豫和转移通道，弯曲模式的耦合，以及在振动弛豫过程中的局部结构和晶体位置的作用。该研究计划为研究生和本科生提供跨学科领域的培训，包括现代光学，材料科学和计算建模。氢是半导体中最重要的杂质之一。氢在这些材料中的一个重要特性是它能够通过钝化缺陷来提高器件性能，这是一种今天在计算机CPU和RAM等集成电路生产中常规使用的工艺。振动能流的速率和途径的知识是理解热和电子刺激的缺陷和杂质的反应和迁移在这些设备中的关键。本实验研究计划的目的是阐明晶体半导体中氢修饰缺陷和杂质复合物局部振动的微观动力学。这些基础研究需要相当低的缺陷或杂质浓度，以减少由于相互作用而产生的影响，这通常会导致材料的红外吸收率低。托马斯杰斐逊国家加速器装置的自由电子激光器的短脉冲高功率可调谐红外辐射将用于高分辨率时间分辨红外吸收实验。氢和氘模式的动力学之间的直接比较，这与这些晶体材料中的体振动有很大的不同的相互作用，将进一步支持能量交换机制的识别。研究生和本科生在从事该项目时将接受的培训将为他们在工业，计算机或政府中有吸引力的半导体或光学相关职业做好准备。

The aim of this research program is to elucidate the dynamics of local vibrational modes (LVMs) of defect and impurity complexes in semiconductors. The research focuses on LVMs in crystalline semiconductors, including the stretch-modes of hydrogen- and deuterium-containing complexes in proton- and deuteron-implanted Si and Ge, the acceptor- and donor-hydrogen complexes in Si and GaAs, and the anti-symmetric stretch-mode of interstitial O in Si, Ge, and GaAs. The population lifetime and the dephasing time of the first excited vibrational level will be determined using transient bleaching and photon-echo measurements. The time-resolved nonlinear-optical studies will be carried out with the short-pulse high-power tunable-infrared radiation of the Free-Electron Laser at the Thomas Jefferson National Accelerator Facility. A comparison between hydrogen- and deuterium-related modes, which have widely different interactions with bulk phonons in crystalline semiconductors, will assist in identifying the relaxation mechanism. Temperature-dependent studies will be performed to elucidate the coupling mechanism between the local modes and the crystal's phonon bands. Several important questions will be addressed regarding vibrational energy relaxation and transfer channels, the coupling to bending-modes, and the role of local structure and crystal site in the vibrational relaxation process. This research program provides training for graduate and undergraduate students in an interdisciplinary field including modern optics, materials science and computational modeling. %%%Hydrogen is one of the most prominent impurities in semiconductors. One important property of hydrogen in these materials is its ability to improve device performance by passivating defects, a process, which today is used routinely in the production of integrated circuits such as CPU and RAM for computers. Knowledge of the rates and pathways of vibrational energy flow is critical for understanding thermally and electronically stimulated defect and impurity reactions and migration in these devices. The aim of this experimental research program is to elucidate the microscopic dynamics of local vibrations of hydrogen-decorated defect and impurity complexes in crystalline semiconductors. These fundamental studies require fairly low defect or impurity concentrations to reduce effects due to interactions, which often results in low infrared absorbance of the material. The short-pulse high-power tunable-infrared radiation of the Free-Electron Laser at the Thomas Jefferson National Accelerator Facility will be employed for high-resolution time-resolved infrared absorption experiments. A direct comparison between the dynamics of hydrogen and deuterium modes, which have widely different interactions with bulk vibrations in these crystalline materials, will further support the identification of the energy exchange mechanism. The training that graduate and undergraduate students will receive while working on this project will prepare them for attractive semiconductor or optics related careers in industry, academe, or government.***