NSF/DMR-BSF: Auger Recombination in Two-Dimensional Quantum Confined Semiconductors

非技术摘要拟议的研究探索纳米级半导体中最基本的工艺之一，这一工艺已知对光电子技术有害。了解这一基本机制可以极大地帮助寻找半导体材料和纳米结构，以最大限度地减少俄歇复合，从而提高光电子学的效率，如现代生活中使用的发光二极管和激光。这些应用的例子包括通信、信息技术、消费电子和照明等。尽管从材料/器件和理论两个角度进行了几十年的研究，但对决定光电子学基本极限的俄歇复合的微观机制知之甚少。为了填补这一关键的知识空白，并制定合理的战略来提高光电子学的效率，PI和合作者将利用他们互补的专业知识，开展一项联合研究计划，以定量探索俄歇重组。美国和以色列两个一流研究机构之间的合作为年轻科学家体验国际合作提供了一个绝佳的机会。在将研究的影响扩展到本科和中学层面方面，PI有着良好的记录，并将扩大他在奥西宁高中科学研究计划中的角色。在提议的休假访问期间，在联合PI的帮助下，PI将在哥伦比亚的研究生和本科生水平上进一步发展成一门完整的课程：研究哲学和伦理学。技术摘要俄歇复合是一个多体过程，其中电子-空穴对的非辐射复合通过将释放的能量/动量转移到第三个电荷载流子或激子而有效地发生。这一过程对光电子技术是不利的，从传统的发光二极管(LED)和激光器到激子或激子-极化子凝聚物的量子设备。PI和合作者将使用两个模型系统定量地探索俄歇复合：二维单层过渡金属二卤化物(TMDCs)和异质结；以及2D有机-无机混合卤化铅钙钛矿(LHPs)。这项研究的目的是从实验上探索俄歇复合如何依赖于能带结构、电子-声子耦合和空间限制，并定量地理解俄歇散射过程的微观机制。只要有可能，PI将实施最直接的实验探测，例如使用飞秒光电子能谱来直接探测俄歇电子散射到特定能量和动量空间时的俄歇电子，使用吸收/发射光谱来确定俄歇复合速率作为空间约束和动量工程的函数，以及使用磁光光谱来识别和量化俄歇复合产生的带电产物(极化子、三子和俘获电荷)以及自旋极化如何影响俄歇复合速率。PI选择这两个模型系统是因为它们的电子结构可以在TMDDC的实空间和动量空间中控制。它们的能带结构对介电屏蔽、异质结中的取向取向和外加磁场都很敏感。LHP被证明是最具吸引力的光电子学材料体系之一，可以生长成2D纳米结构，可以通过卤化铅层的数量轻松控制量子限制。此外，由于强烈的自旋-轨道耦合(SOC)和局部对称性反转而提出的拉什巴效应可能允许通过外部电磁或磁场控制能带结构。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL ABSTRACTThe proposed research probes one of the most fundamental processes in nanoscale semiconductors, a process known to be detrimental to optoelectronic technologies. Understanding this fundamental mechanism may greatly aid the search for semiconductor materials and nanostructures to minimize Auger recombination, thus increasing the efficiency of optoelectronics, such as light emitting diodes and lasers used in all aspects of modern life today. Examples of these applications include, among others, communication, information technology, consumer electronics, and lighting. Despite decades of research from both materials/device and theoretical perspectives, little is known about the microscopic mechanisms of Auger recombination that determine fundamental limits of optoelectronics. To fill this critical knowledge gap and formulate rational strategies to increase the efficiency of optoelectronics, the PI and collaborator will take advantage of their complementary expertise and carry out a joint research program to quantitatively probe Auger recombination. The collaboration between two premier research institutions in the US and Israel provides an excellent opportunity for young scientists to experience international collaboration. The PI has had a strong track record of extending the impact of research to undergraduate and secondary school levels and will expand his role in the Science Research Program at Ossining High School. With the help of the co-PI during a proposed sabbatical visit, the PI will further develop "Research Philosophy and Ethics" to a full course at the graduate and undergraduate level at Columbia.TECHNICAL ABSTRACTAuger recombination is a many-body process in which the non-radiative recombination of an electron-hole pair occurs efficiently by transferring the released energy/momentum to a third charge carrier or an exciton. This process is detrimental to optoelectronic technologies, ranging from conventional light emitting diodes (LEDs) and lasers to quantum devices of exciton or exciton-polariton condensates. The PI and collaborator will quantitatively probe Auger recombination using two model systems: two dimensional (2D) monolayer transition metal dichalcogenides (TMDCs) and heterojunctions; and 2D hybrid organic-inorganic lead halide perovskites (LHPs). The objective of the proposed research is to experimentally probe how Auger recombination depends on the band structure, electron-phonon coupling, and spatial confinement, and to quantitatively understand the microscopic mechanisms underlying the Auger scattering process. Whenever possible, the PIs will implement the most direct experimental probes, e.g., using femtosecond photoemission spectroscopy to directly detect Auger electrons as they scatter into particular energy and momentum spaces, absorption/emission spectroscopies to determine Auger recombination rates as functions of spatial confinement and momentum engineering, and magneto-optical spectroscopies to identify and quantify charged products (polarons, trions, and trapped charges) from Auger recombination and how spin polarization can influence Auger recombination rates. The PIs choose the two model systems because their electronic structures can be controlled in real and momentum spaces in TMDCs. Their band structures are sensitive to dielectric screening, to orientation alignment in heterojunctions, and to external magnetic field. The LHPs, demonstrated as one of the most attractive material systems for optoelectronics, can be grown into 2D nanostructured, allowing easy control of quantum confinement by the number of lead halide layers. Moreover, the proposed Rashba effect due to strong spin-orbital-coupling (SOC) and breaking of local inversion of symmetry may allow the control of band structure by external electric or magneticThis 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.