Materials World Network: Terahertz Spectroscopy of Modulation Doped Si and SiGe Nanostructures

该材料世界网络奖授予特拉华大学，以表彰对调制掺杂硅和硅锗纳米结构中浅掺杂的实验和理论研究。由于组成、界面和合成方法之间的复杂材料相互作用，纳米结构中的掺杂剂具有不寻常的行为。纳米结构中的应变可以将掺杂能级推入能带，产生具有增强发光的共振态，而纳米结构的调制掺杂可能会产生新的功能，就像它对块体材料和薄膜所做的那样。然而，纳米结构中的掺杂剂的性质还没有被很好地理解，而且关于影响载流子的能态和输运的机制还存在一些基本的问题。因此，很难区分与根本和过程相关的影响。为了更好地理解，研究人员将研究杂质和连续态的不同局域态和共振态之间的辐射太赫兹跃迁，以及载流子输运现象。我们将从实验和理论上得到由应变和空间量子化分裂的二维杂质态的能谱、态密度、俘获和电离率以及光学跃迁几率。生长技术将是分子束外延和化学气相沉积，以实验和理论为指导，揭示基本原理。表征技术将是与温度相关的太赫兹电致发光光谱和电流-电压测量。实验结果将与模拟和建模进行交互比较，以完善理论并指导生长条件的选择，以创建具有特定参数的掺杂纳米结构。本文计划的方法可以提供有关SiGe纳米结构中杂质跃迁和态的光谱特征以及影响辐射发射频率和强度的材料参数的新信息。一个特殊的目标是研究杂质态布居数反转的条件和起源，并阐明调制掺杂Si和SiGe结构中的这些机制。这项研究可能产生的技术后果是，在器件尺寸缩小时指导掺杂剂的选择，并根据掺杂剂中的辐射跃迁识别新的器件家族的现象。该项目将与Ioffe物理技术研究所(圣彼得堡)和放射工程和电子学研究所(莫斯科)的俄罗斯科学家合作进行。组建的团队拥有互补的专业知识和设施来进行拟议的研究。该奖项将为学生和初级和高级研究人员在这一国际合作中提供教育和发现的机会。特拉华大学和俄罗斯的科学家们的这项合作研究可能会使人们更好地理解掺杂的SiGe纳米结构的合成和性质，并识别作为载流子传输和辐射跃迁基础的机制。在一个重要的技术材料项目中对学生进行教育和培训是拟议的国际合作的一个关键方面。此外，该计划的成果将被纳入特拉华大学的课程，研究的要点将在一个网页上展示，该网页旨在向学生和普通公众提供纳米结构的教育信息。

This Materials World Network award to University of Delaware is for experimental and theoretical studies on shallow dopants in modulation-doped silicon and silicon-germanium nanostructures. Dopants in nanostructures have unusual behavior because of complex materials interactions between the composition, interfaces, and the method of synthesis. Strain in nanostructures can push the dopant levels into the band creating a resonant state with enhanced luminescence, and the modulation doping of nanostructures may produce novel functionality as it has done for bulk materials and thin films. The properties of dopants in nanostructures have not been well understood, however, and there are fundamental questions regarding the mechanisms that affect the energy states and transport of charge carriers. As a result, it has been difficult to distinguish between fundamental and process related influences. To achieve a greater understanding, the investigators will study radiative terahertz transitions between different localized and resonant states of impurities and continuum states, as well as carrier transport phenomena. The energy spectra, density of states, capture and ionization rates of two dimensional impurity states split by strain and space quantization, and the probabilities of optical transitions will be obtained experimentally and theoretically. The growth techniques will be molecular beam epitaxy and chemical vapor deposition, guided by experiments and theory to uncover fundamental principles. The characterization techniques will be temperature dependent terahertz electroluminescence spectroscopy and current versus voltage measurements. The results of experiments will be compared with simulations and modeling interactively, to refine theories and to guide the choice of growth conditions for creating doped nanostructures with specific parameters. The approaches planned here can yield new information on the spectral features of impurity transitions and states in SiGe nanostructures, and the materials parameters that affect the radiative emission frequency and intensity. A special objective is to investigate the conditions for, and origin of population inversion in impurities states, and to clarify these mechanisms in modulation doped Si and SiGe structures. Possible technological consequences for this research would be to guide the selection of dopants as device sizes shrink, and to identify phenomena for new families of devices based on radiative transitions in dopants. The project will be carried out in collaboration with Russian scientists at Ioffe Physico-Technical Institute (St. Petersburg), and the Institute of Radioengineering and Electronics (Moscow). The assembled team has complementary expertise and facilities to conduct the proposed research. The award will provide opportunities for education and discovery in this international collaboration by students and junior and senior researchers. This collaborative research between scientists at University of Delaware and Russia could lead to a greater understanding of the synthesis and properties of doped SiGe nanostructures, and the identification of mechanisms that underlie carrier transport and radiative transitions. The education and training of students in a technologically important materials project is a pivotal aspect of the proposed international collaboration. In addition the results of this program will be incorporated into courses at the University of Delaware, and highlights of research will be featured on a web page designed to provide educational information on nanostructures to students and the general public.