RUI: Ultrafast THz Spectroscopy of Spin Dynamics in Semiconductors

本项目将使用超快太赫兹光谱来研究窄间隙半导体量子阱中的自旋激发。这些系统表现出很大的自旋-轨道耦合，允许载流子的自旋状态被一个电场控制，比如来自栅极接触的电场。这些系统将用一个时间分辨光谱探针来研究，该探针调谐到自旋轨道相互作用的能量尺度（1-5meV）。将确定若干量子阱结构的自旋激发的寿命和能谱。这种测量是通过自旋轨道相互作用实现的，这将允许在定义良好的自旋状态下光学产生载流子，以及自旋演化的光学探针。超快太赫兹光谱学也将用于在太赫兹频率下对InAs中的供体电子进行脉冲epr测量。这些实验的成功表现将证明该技术适用于广泛的物理系统。在图案化半导体表面上产生太赫兹频率也将被研究。预计表面图像化将使半导体表面产生光泵太赫兹脉冲的效率提高约一个数量级。最后，载流子寿命将研究皮秒载流子寿命材料，如低温生长GaAs和辐射损伤半导体。本科生将参与这项研究，该研究将在马卡莱斯特学院和明尼苏达大学进行。该项目还将受益于与工业伙伴的合作。因此，学生也将在一个主要的研究企业中获得研究经验。随着技术的进步将晶体管的尺寸推向原子尺寸，它们的性质将越来越多地受到量子力学的影响。出于这个原因，科学家们正在探索依赖量子现象实现其功能的设备。其中一个很有前途的领域涉及半导体器件，其中电子的自旋而不是电荷被用来控制电流的流动。目前，实现这种半导体自旋输运器件的最有前途的系统是薄层材料，如砷化铟和锑化铟。然而，实现这些新技术需要详细了解这些系统中电子自旋在超短时间间隔内的行为。本研究利用红外光谱在万亿分之一秒的时间分辨率下对砷化铟和锑化铟的光学性质进行了实验研究。这样的测量将揭示改变这些系统中自旋的方向需要多少能量，以及自旋在新定向状态下保持多长时间。将进行额外的实验来证明脉冲磁共振波谱在这些超短时间尺度上的可行性。这项研究将在麦卡莱斯特学院和明尼苏达大学进行。该项目还将受益于一个工业合作者的参与。本研究将由本科生参与。他们将因此获得凝聚态物理和材料科学前沿领域的技能和知识。他们将在了解先进技术的需要和进入科学/技术工作队伍的情况下为高级研究做好准备。

This project will use ultrafast THz spectroscopy to study spin excitations in narrow-gap semiconductor quantum wells. These systems exhibit a large spin-orbit coupling, permitting the spin-state of carriers to be controlled with an electric field such as that from a gate contact. These systems will be investigated with a time-resolved spectroscopic probe tuned to the energy scale of the spin-orbit interaction (1-5meV). The lifetimes and energy spectra of spin excitations will be determined for a number of quantum well structures. Such measurements are made possible by the spin-orbit interaction, which will allow optical generation of carriers in a well-defined spin-state, and optical probes of the evolution of spins. Ultrafast THz spectroscopy will also be used to perform pulsed-EPR measurements at terahertz frequencies on donor electrons in InAs. The successful performance of these experiments will demonstrate the applicability of this technique to a wide range of physical systems. Terahertz frequency generation on patterned semiconductor surfaces will also be investigated. It is expected that surface patterning will boost the efficiency of generation of optically pumped THz pulses from semiconductor surfaces by about one order of magnitude. Lastly, carrier lifetimes will be investigated in picosecond carrier-lifetime materials such as low-temperature grown GaAs and radiation damaged semiconductors. Undergraduate students will participate in this research which will be performed at Macalester College and the University of Minnesota. The project will also benefit from collaboration with an industrial partner. The students will thus also acquire research experience in a setting of a major research enterprise. %%%As advances in technology push the size of transistors towards atomic dimensions, their properties will be increasingly influenced by quantum mechanics. For this reason, scientists are exploring devices that rely on quantum phenomena for their function. One such promising area involves semiconductor devices in which an electron's spin, rather than its charge, is used to control the flow of electric current. At the present time the most promising systems for realizing such semiconductor spin-transport devices are thin layers of materials such as indium arsenide and indium antimonide. Realizing these new technologies requires, however, a detailed understanding of the behavior of electron spins in these systems at ultra-short time intervals. This research is devoted to an experimental investigation of the optical properties of indium arsenide and indium antimonide by means of infrared spectroscopy at a time resolution of one trillionth of a second. Such measurements will reveal how much energy is required to change the direction of the spin in these systems, and how long the spin remains in the newly oriented state. Additional experiments will be performed to demonstrate the feasibility of pulsed magnetic resonance spectroscopy at these ultra-short time scales. This research will be conducted at Macalester College as well as at the University of Minnesota. The project will also benefit from the participation of an industrial collaborator. Undergraduate students will be engaged in this research. They will thereby acquire skills and knowledge in a forefront area of condensed matter physics and materials science. They will be prepared for advanced studies with an appreciation for the needs of advanced technology and for entry into the scientific/technological workforce.