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

摘要：杂化金属卤化物钙钛矿已成为一类很有前途的半导体材料，在太阳能电池、发光二极管和晶体管等器件中有着广泛的应用。这些材料还具有较大的自旋轨道耦合，这使得这些钙钛矿成为自旋电子器件的候选材料。自旋电子学将电子学与基本粒子的固有特性——自旋结合起来，使数据存储或高级计算的节能设备等新技术成为可能。由无机半导体（如硅或锗）交替层制成的基于量子阱的自旋电子器件通过外延生长制造成本很高。相比之下，具有由有机层和无机层交替组成的天然量子阱结构的二维杂化钙钛矿可以通过低成本、简便的溶液处理来制造。尽管钙钛矿满足可行的自旋电子器件的几个重要先决条件，但在这种新型量子阱中缺乏对自旋相关现象的基本理解。在这个项目中，研究小组将光学探测和操纵混合钙钛矿量子阱中的自旋。该项目将产生对这些材料的自旋自由度的基本理解。这些知识将有助于为材料合成和高效、经济的自旋电子器件的器件工程制定指导方针。研究生和本科生，特别是来自代表性不足群体的学生，将参与多层次的研究活动。通过面向初高中学生的“EXPO物理”和面向小学生的“Show-n-tell in Physics”等科学展览，普通大众将参与其中。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-HOIPs）近年来开始在新的领域进行改造。这些材料具有强的自旋轨道耦合、高电荷迁移率和具有多界面和易于溶液处理的本征量子阱结构。巨大的Rashba分裂在这些材料中得到了实验证实，突出了它们在具有成本效益的室温自旋电子器件中的潜力。然而，仍有几个关键问题需要解决，以扫清通往可行设备的道路。核心问题是如何在二维HOIP多量子阱中产生和控制自旋光电流。该项目的目标是通过全面研究自旋光电流对量子阱结构、晶体对称性和缺陷的依赖，加深对这种新型多量子阱的基本认识。通过改变无机层数，可以很容易地将HOIP中的量子阱结构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）的作用将发生变化。本研究的重点是利用光电光谱表征“激子”和“自由载流子”量子阱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Rashba/Dresselhaus效应的信息，研究激子自旋极化电流的来源，并通过光电光谱表征自由和束缚激子的自旋极化。从该项目中获得的知识有望补充在二维电子气量子阱中研究得很好的自旋光物理学，并为从事光电子和自旋电子学应用的科学家提供信息。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。

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.