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

特拉华州大学的材料世界网络奖是对调制掺杂硅和硅锗纳米结构中浅掺杂剂的实验和理论研究。纳米结构中的掺杂剂具有不寻常的行为，这是因为组成、界面和合成方法之间的复杂材料相互作用。 纳米结构中的应变可以将掺杂剂水平推到产生具有增强发光的共振态的带中，并且纳米结构的调制掺杂可以产生新的功能，正如它对块体材料和薄膜所做的那样。 然而，纳米结构中掺杂剂的性质还没有得到很好的理解，并且存在关于影响电荷载流子的能量状态和传输的机制的基本问题。因此，很难区分基本影响和过程相关影响。为了更好地理解，研究人员将研究杂质和连续态的不同局部和共振态之间的辐射太赫兹跃迁，以及载流子输运现象。 通过实验和理论计算，得到了应变和空间量子化分裂的二维杂质态的能谱、态密度、俘获率和电离率，以及光跃迁几率。 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。表征技术将是温度相关的太赫兹电致发光光谱和电流与电压的测量。 实验结果将与模拟和建模进行比较，以完善理论并指导选择生长条件，以创建具有特定参数的掺杂纳米结构。这里计划的方法可以产生新的信息的光谱特征的杂质跃迁和状态的SiGe纳米结构，以及影响辐射发射频率和强度的材料参数。 一个特殊的目标是调查的条件，和起源的杂质状态的粒子数反转，并澄清这些机制在调制掺杂的Si和SiGe结构。 这项研究可能的技术后果将是指导掺杂剂的选择作为设备尺寸缩小，并确定基于掺杂剂的辐射跃迁的新系列设备的现象。该项目将与Ioffe物理技术研究所（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。集合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。特拉华州大学和俄罗斯科学家之间的这项合作研究可能会导致对掺杂SiGe纳米结构的合成和特性的更好理解，以及对载流子传输和辐射跃迁机制的识别。在一个技术上重要的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，该计划的结果将纳入特拉华州大学的课程，研究的亮点将在一个网页上展示，该网页旨在向学生和公众提供有关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.