Theory of Spin Transport in Silicon Nanostructures

超越cmos时代的未来技术正成为极其重要的研究前沿。在这一点上，科学家们推测，基于自旋的设备肯定即将出现。在这些器件中，量子力学自旋被引入到电子电路中。硅是制作自旋电子器件的理想材料。它拥有压倒性主导半导体行业的成熟技术。重要的是，硅具有相对较长的自旋弛豫时间，这是由于其弱的自旋-轨道耦合和重要的自旋松弛机制的抑制(通过其自然丰富的同位素的晶体反转对称性和零核自旋)。因此，自旋信息可以在硅中携带超过1毫米的长度。所提出的活动的智能优点：I.研究在应变、电场和量子化存在的情况下硅器件中的自旋弛豫。在这一部分中，基本的器件几何结构包括自旋注入器和探测器之间的传输通道。通过这一基本结构的输运将使用漂移-扩散模型来研究，该模型的基本参数(例如，自旋寿命和电荷迁移率)将通过精确量化电子-声子相互作用的严格数值方法来计算。其中包括计算电子波函数的经验赝势方法和k&p模型，以及计算声子色散和原子位移矢量的绝热键电荷模型。应变效应可以很容易地包含在这些模型中，而沿限制方向的量子化效应在k&amp；p模型中被明确考虑。电子-声子散射将用刚性离子近似来模拟。将使用群论来确定简化分析的选择规则。将所获得的知识融入到器件模拟中。自旋注入、引出和接触宽度的作用将由从验证的实验结果中获得的现实边界条件来进行。将研究一种基于自旋的片内信息传输的新概念，它可以缓解片上传输线的许多尖锐问题。我们将用蒙特卡罗模拟方法研究硅线和硅-锗纳米结构器件中(电场作用下)漂移传导电子的加热效应。蒙特卡罗模拟将量化电荷输运和自旋寿命。除了自旋翻转，动量松弛将由电子-晶格和电子-杂质散射来模拟。拟议活动的更广泛影响：拟议的研究包括硅自旋电子学的新理论方面和器件概念。这项研究是及时的，可能会产生重要的影响，因为自旋注入硅最近已经成为一个非常活跃的研究领域。除了在同行评议的期刊上发表文章和在专业会议上发表演讲外，该项目的成果(理论预测和设备模型结果)将与硅自旋电子学的领先实验者共享。我们之前的自旋电子学结果的广泛影响已经在几本科学杂志上得到了强调，包括《科学新闻》、《纳米材料新闻》和《新科学家》。教育活动是该项目的重要组成部分，并与拟议方案紧密结合。这项拟议的研究提出的想法吸引了广泛的学生。通过工程和物理研究生的合作，双方都可以学习其他量子力学或设备函数的概念。PI已经设计了一门关于自旋电子学的新课程，解释了如何将量子力学和磁学应用到新的逻辑和存储体系结构中。PI致力于培养学生，并将把这项研究与本科课程相结合，并将招收合格的本科生参与研究。PI将通过提供互动讲座/演示，强调未来技术在设备中的使用，在K-12学生中积极促进这项研究。这项研究具有很高的社会影响力，有望吸引来自代表性不足群体的学生参与该项目。

Future technologies beyond the CMOS age are becoming exceedingly important research frontiers. In this regard, scientists conjectured that spin-based devices must be on the horizon. In these devices, the quantum mechanical spin is introduced to electronic circuits. Silicon is an ideal material choice for spintronic devices. It has a mature technology which overwhelmingly dominates the semiconductor industry. Importantly, silicon has a relatively long spin relaxation time due to its weak spin-orbit coupling and the suppression of important spin relaxation mechanisms (via the crystalline inversion symmetry and the zero nuclear spin of its naturally abundant isotope). Accordingly, spin information can be carried over 1 mm length scales in silicon.Intellectual Merit of the proposed activity:I. Studying the spin relaxation in silicon devices in the presence of strain, electrical fields and quantization. In this part, the basic device geometry includes a transport channel between spin injector and detector. Transport across this basic structure will be studied using a drift-diffusion model whose basic parameters (e.g., spin lifetime and charge mobility) will be calculated from rigorous numerical methods that accurately quantify the electron-phonon interaction. These include an empirical pseudopotential method and a k∙p model to calculate the electron wavefunctions and an adiabatic bond-charge model to calculate the phonon dispersion and atom displacement vectors. Strain effects can be readily incorporated in these models while quantization effects along the confinement direction are explicitly considered in the k∙p model. The electron-phonon scattering will be modeled by a rigid-ion approximation. Group theory will be used to identify selection rules that simplify the analysis. II. Incorporating the gained knowledge in device simulations. Spin injection, extraction and the role of contact widths will be carried by realistic boundary conditions taken from verified experimental results. A new concept for on-chip spin-based information transfer that alleviates much of the acute problems of on-chip transmission lines will be studied. Heating effects of drifting conduction electrons (by the electric field) in silicon wires and silicon-germanium nanostructure devices will be investigated by Monte Carlo simulations which quantify both the charge transport and spin lifetime. Other than spin flips, momentum relaxation will be modeled by electron-lattice and electron-impurity scattering. Broader impacts of the proposed activity:The proposed research includes new theoretical aspects and device concepts in silicon spintronics. This research is timely and may have an important impact since spin injection in silicon has recently become a very active research field. Other than publications in peer-reviewed journals and presentations in professional conferences, outcomes of this project (theoretical predictions and device model results) will be shared with leading experimentalists in silicon spintronics. The broad impact of our previous spintronics results has been highlighted in several science magazines including the Science News, Nanomaterials News and the New Scientist. Educational activities are an essential part of this project and are closely integrated with the proposed program. The proposed research presents ideas that are fascinating to a wide range of students. By collaboration of engineering and physics graduate students, each side learns from the other quantum mechanics or device function concepts. The PI has already designed a new course on spintronics which explains how quantum mechanics and magnetism can be applied into new logic and memory architectures. The PI is committed to training students and will integrate this research with undergraduate courses and will recruit qualified undergraduate students to participate in the research. The PI will actively promote this research among K-12 students by delivering interactive lectures/demos that highlight the use of future technology in devices. The potential of this research for high societal impact will hopefully attract students from under-represented groups to the project.