RUI: Ultrafast THz Spectroscopy of Spin Dynamics in Semiconductors

本计画将利用超快太赫兹光谱技术来研究窄隙半导体量子威尔斯井中的自旋激发。这些系统表现出大的自旋-轨道耦合，允许载流子的自旋状态用诸如来自栅极接触的电场来控制。这些系统将与时间分辨的光谱探针调谐到自旋轨道相互作用的能量尺度（1- 5 meV）进行研究。自旋激发的寿命和能谱将被确定为一些量子阱结构。这样的测量是可能的自旋轨道相互作用，这将允许光学产生的载体在一个明确的自旋状态，和光学探针的演变自旋。 超快太赫兹光谱也将用于在太赫兹频率下对InAs中的施主电子进行脉冲EPR测量。这些实验的成功将证明这种技术对广泛的物理系统的适用性。也将研究图案化半导体表面上的太赫兹频率产生。预计表面图案化将使从半导体表面产生光泵浦THz脉冲的效率提高约一个数量级。 最后，载流子寿命将在皮秒载流子寿命的材料，如低温生长的GaAs和辐射损伤的半导体研究。 本科生将参加这项研究，将在麦卡莱斯特学院和明尼苏达大学进行。该项目还将受益于与工业合作伙伴的合作。因此，学生也将在一个主要的研究企业的设置获得研究经验。 随着技术的进步将晶体管的尺寸推向原子尺寸，它们的特性将越来越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于量子现象来实现其功能的设备。其中一个很有前途的领域涉及半导体器件，在这种器件中，电子的自旋而不是电荷被用来控制电流的流动。目前，用于实现这种半导体自旋输运器件的最有希望的系统是诸如砷化铟和锑化铟的材料的薄层。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极短时间间隔内的行为。 本研究致力于砷化铟和锑化铟的光学性质的实验研究，通过红外光谱的时间分辨率为万亿分之一秒。这样的测量将揭示在这些系统中需要多少能量来改变自旋的方向，以及自旋保持在新取向状态的时间。将进行额外的实验，以证明在这些超短时间尺度的脉冲磁共振光谱的可行性。 这项研究将在麦卡莱斯特学院和明尼苏达大学进行。该项目还将受益于工业合作者的参与。 本科生将从事这项研究。 因此，他们将获得凝聚态物理和材料科学前沿领域的技能和知识。 他们将为高级研究做好准备，了解先进技术的需求，并进入科学/技术劳动力市场。

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.