Study of spin photocurrent in 2D hybrid organic-inorganic perovskite multiple quantum wells

非技术摘要：混合金属卤化物钙钛矿已经成为一类有前途的半导体，在太阳能电池，发光二极管和晶体管中具有器件应用。这些材料还具有大的自旋轨道耦合，这使得这些钙钛矿成为自旋电子器件的候选者。自旋电子学将电子学与自旋（基本粒子的固有属性）相结合，以实现新技术，如用于数据存储或高级计算的节能设备。基于由诸如硅或锗的无机半导体的交替层制成的量子威尔斯的自旋电子器件通过外延生长制造是昂贵的。相比之下，具有由交替的有机层和无机层组成的天然量子阱结构的二维混合钙钛矿可以通过低成本、容易的溶液处理来制造。虽然钙钛矿满足可行的自旋电子器件的几个重要先决条件，但对这种新型量子阱中的自旋相关现象缺乏基本的了解。在该项目中，研究团队将光学探测和操纵混合钙钛矿量子威尔斯中的自旋。该项目将产生在这些材料的自旋自由度的基本理解。这些知识将有助于制定指导方针，材料合成和设备工程的高效和成本效益的自旋电子器件。研究生和本科生，特别是那些来自代表性不足的群体，将参加多层次的研究活动。通过面向中学生的“EXPO Physics”和面向小学生的“Show-n-tell in Physics”等科学展览，让公众参与进来。技术摘要具有Ruddlesten-Popper层状结构的二维杂化有机无机钙钛矿（2D-HOIP）最近开始改变新的领域。这些材料具有强的自旋轨道耦合、高的电荷迁移率、具有多界面的本征量子阱结构和易溶液加工性。实验证实了这些材料中的巨大Rashba分裂，突出了它们作为具有成本效益的室温自旋电子器件的潜力。然而，仍有一些关键问题需要回答，以清除通往可行设备的道路。中心问题是如何在二维HOIP多量子阱中产生和操纵自旋光电流。该项目的目标是通过对自旋光电流对量子阱结构、晶体对称性和缺陷的依赖性进行全面研究，加深对这种新型多量子阱的基本理解。HOIP中的量子阱结构可以通过改变无机层的数量而容易地从纯二维调谐到准三维。假设激子（在二维中占主导地位）和自由载流子（在三维中占主导地位）的角色将发生变化。本计画的重点是利用光电流光谱来描述“激子”与“自由载子”量子威尔斯中自旋光电流行为的差异。本研究的目的是测量自由载流子的自旋光电流，提取有关Rashba/Dresselhaus效应的信息，研究激子的自旋极化电流的起源，并通过光电流光谱表征自由和束缚激子的自旋极化。从这个项目中获得的知识有望补充自旋电子物理学在二维电子气量子威尔斯中的研究，并为从事光电和自旋电子学应用的科学家提供信息。这个奖项反映了NSF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。

Non-technical Abstract:Hybrid metal halide perovskites have emerged as a promising class of semiconductors with device applications in solar cells, light emitting diodes and transistors. These materials also have large spin-orbit coupling, which makes these perovskites a candidate for spintronic devices. Spintronics combines electronics with spin, an intrinsic property of elementary particles, to enable novel technologies such as energy efficient devices for data storage or advanced computing. Spintronic devices based on quantum wells made by alternating layers of inorganic semiconductors such as silicon or germanium are expensive to make by epitaxial growth. In contrast, a two-dimensional hybrid perovskite with a natural quantum well structure consisting of alternating organic and inorganic layers can be fabricated via low-cost, facile solution processing. Although perovskites meet several important prerequisites for viable spintronic devices, there is lack of fundamental understanding of the spin-related phenomena in this new type of quantum well. In this project, the research team will optically probe and manipulate spins in hybrid perovskite quantum wells. The project will yield a fundamental understanding of spin degree of freedom in these materials. This knowledge will help to develop guidelines for material synthesis and device engineering for efficient and cost-effective spintronic devices. Graduate and undergraduate students, particularly those from underrepresented groups, will participate in multi-level research activities. The general public will be involved through scientific exhibitions such as ‘EXPO Physics’ for middle and high school students and ‘Show-n-tell in Physics’ for elementary school students.Technical AbstractTwo-dimensional hybrid organic inorganic perovskites (2D-HOIPs) with a Ruddlesten-Popper layered structure have recently started transforming new fields. These materials have strong spin-orbit coupling, high-charge mobility, and an intrinsic quantum well structures with many interfaces and facile solution processability. Giant Rashba splitting was experimentally confirmed in these materials, highlighting their potential for cost-effective room temperature spintronic devices. However, a few key questions remain that need to be answered to clear the pathway to viable devices. The central question is how spin photocurrent is generated and manipulated in two-dimensional HOIP multiple quantum well. The goal of the project is to deepen the fundamental understanding of this new type of multiple quantum well by conducting a comprehensive study on spin photocurrent dependence on quantum well structure, crystal symmetry and imperfection. The quantum well structure in a HOIP can be easily tuned from pure two dimensional to quasi three dimensional by varying the number of inorganic layers. Hypothetically, the roles of excitons (dominant in two dimension) and free carriers (dominant in three dimension) will shift. The focus of this proposal is to characterize the difference of spin photocurrent behaviors in ‘excitonic’ and ‘free carrier’ quantum wells using photogalvanic spectroscopy. The objectives of the study are to measure spin photocurrent for free carriers and extract the information about Rashba/Dresselhaus effects, investigate the origin of spin-polarized current from excitons, and characterize the spin polarization of free and bound excitons through photogalvanic spectroscopy. The knowledge gained from this project is expected to complement the spin-photophysics well studied in two-dimensional electron gas quantum wells, and be informative to scientists working in optoelectronic and spintronics applications.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.