Bipolar Spintronic Devices with Two-Dimensional Systems

在半导体器件中，载流子（电子和带相反电荷的空穴）的重组导致光（光子）的发射发挥着越来越重要的作用。2014年诺贝尔物理学奖认可的发光二极管（led）的进步，比传统灯泡展示了许多优点，包括更低的功耗，更长的使用寿命，更小的尺寸，减少了对环境的担忧。虽然led和激光器的重点是发射波长和强度，但通过利用发射光的偏振，它们的效用可以显著增强。类似于人类偏爱的手（左vs右），光的偏振可以显示手性（左vs右或顺时针vs逆时针）。这种偏好也是许多其他方面相同的分子所固有的，可以表明不同的生物功能。偏振敏感检测可用于生物医学诊断，包括癌症的早期检测。提出的研究研究了发光二极管和激光器的偏振控制，以提高它们的检测灵敏度，以及实现更快的操作和更低的功耗。这种偏振控制背后的原理是总角动量在不同子系统（如载流子和光子）之间转换时的守恒。在一个简单的力学表现中，角动量守恒导致滑冰运动员的旋转频率增加，当他们的手臂被拉近他们旋转的身体。在发光装置中，载流子的角动量与它们的自旋有关，这类似于儿童的陀螺沿顺时针或逆时针方向旋转。通过优先自旋于其中一个方向的自旋极化载流子角动量的传递，发射的光变得极化。建议的工作将提供紧密结合的教育和推广工作，以及开发研究自旋电子学的资源，包括自旋电子学手册：自旋输运和磁性，第二版，由PI共同编辑。为了解决中等教育中的一个缺陷，即绝大多数公立学校的学生很少或没有接触过物理科学，从而阻碍了他们考虑从事科学或工程方面的职业，PI将组织暑期讲习班：发光二极管和激光。主题将包括光衍射，波长测量，激光的偏振特性，以及激光输出的修改。作为一年一度的SPIE：光学+光子学会议的一部分，PI将组织专题讨论会，以弥合自旋电子学和光学社区之间的差距。在室温下工作的实际自旋电子器件的成功很大程度上限于单极器件，其中自旋极化电子负责自旋阀中实现的磁阻效应。尽管它们在磁存储和传感方面取得了显著的成功，但这种自旋阀在高级信号处理和数字逻辑方面的应用有限。因此，重要的是评估是否有替代途径来实现潜在的变革性自旋基器件，而不是磁电阻。研究人员寻求了两种通往优越发光器件的途径：(1)使用传统的半导体；(2)使用可以制造成原子级薄的新型范德华材料。在(1)中，预测硅作为传统电子的主要材料，但其光学性能较差，也可能导致强大的光发射，从而为硅光电子提供未开发的机会。在(2)中，原子薄的有源区域可以减小尺寸，并且光的发射以传统对应物消耗的一小部分功率实现。与旨在增加载流子自旋弛豫时间的基于自旋的器件的常见方法相反，预测短的自旋弛豫时间支持发射光偏振的超快变化（300 K时200 GHz），从而实现超快光通信。理论预测将通过实验合作得到密切支持，以确保其论证。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Semiconductor devices in which the recombination of carriers (electrons and oppositely charged holes) leads to the emission of light (photons) play an increasingly important role. Advances in light emitting diodes (LEDs), recognized by the 2014 Nobel Prize in Physics, demonstrate many advantages over conventional light bulbs, including lower power consumption, longer lifetime, smaller size, and reduced environmental concerns. While in LEDs and lasers the focus is on the emission wavelength and intensity, their utility can be significantly enhanced by also harnessing the polarization of the emitted light. Akin to a preferred hand use in humans (left vs right), the polarization of light can display handedness (left vs right or clockwise vs counterclockwise). This preference is also inherent to many otherwise identical molecules and can signal different biological functions. The polarization-sensitive detection can be used for biomedical diagnosis, including an early detection of cancer. The proposed research investigates polarization control in light emitting diodes and lasers to improve their detection sensitivity as well as enable a much faster operation and lower power consumption. The principle behind this polarization control is the conservation of the total angular momentum when it is converted between different subsystems, such as carriers and photons. In a simple mechanical manifestation, the conservation of angular momentum causes the rotational frequency of ice skaters to increase when their arms are pulled closer to their spinning bodies. In light emitting devices the angular momentum of carriers is associated with their spin that is analogous to a child's top spinning in the clockwise or counterclockwise direction. Through transfer of angular momentum of spin-polarized carriers that preferentially spin in one these directions, the emitted light becomes polarized. The proposed work will provide a closely integrated educational and outreach efforts, as well as develop resources to study spintronics, including Spintronics Handbook: Spin Transport and Magnetism, 2nd Edition, co-edited by the PI. To address a deficiency in the secondary education in which a vast majority of public school students have minimal or no exposure to physical sciences that subsequently deters them from considering careers in science or engineering, the PI will organize Summer Workshops: Light Emitting Diodes and Lasers. The topics will include light diffraction, wavelength measurement, polarization properties of lasers, and modification of laser output. As a part of the annual SPIE: Optics+Photonics Conference, the PI will organize Symposia to bridge the gap between the spintronics and optics communities.The success of practical spintronic devices operating at room temperature is largely limited to unipolar devices where spin-polarized electrons are responsible for magnetoresistive effects implemented in spinvalves. Despite their remarkable success for magnetic storage and sensing, such spin valves are of limited use for advanced signal processing and digital logic. It would therefore be important to assess if there are alternative paths to realize potentially transformative spin-based devices, beyond magnetoresistance. Two paths towards superior light emitting devices are sought: (1) using conventional semiconductors and (2) using novel van der Waals materials that can be made atomically thin. In (1) it is predicted that silicon as the dominant material for conventional electronic, but with poor optical properties, could also lead to the robust light emission and thereby provide unexplored opportunities for silicon optoelectronics. In (2) an atomically-thin active region enables reduction in size and the emission of light is achieved at a fraction of the power consumed in conventional counterparts. In contrast to the common approach for spin-based devices that aims to increase the carrier spin relaxation time, it is predicted that short spin relaxation time supports ultrafast changes in the polarization of the emitted light ( 200 GHz at 300 K) and thereby enables ultrafast optical communication. Theoretical predictions will be closely supported through experimental collaborations to ensure their demonstration.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.