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

摘要本研究探讨了纳米级半导体中最基本的过程之一，这一过程已知对光电技术有害。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，例如在现代生活的各个方面使用的发光二极管和激光器。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/器件和理论角度进行了数十年的研究，但人们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，制定合理的策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，定量地探测俄歇重组。美国和以色列两个主要研究机构之间的合作为年轻科学家提供了体验国际合作的绝佳机会。PI在将研究的影响扩展到本科和中学水平方面有着良好的记录，并将扩大他在奥西宁高中科学研究计划中的作用。在联合项目负责人的帮助下，项目负责人将在哥伦比亚大学的研究生和本科生阶段进一步发展“研究哲学和伦理学”课程。技术摘要俄歇复合是一种多体过程，通过将释放的能量/动量传递给第三载流子或激子，有效地实现电子-空穴对的非辐射复合。这一过程不利于光电子技术，从传统的发光二极管（led）和激光到激子或激子-极化子凝聚体的量子器件。PI和合作者将使用两种模型系统定量探测俄歇重组：二维（2D）单层过渡金属二硫化物（TMDCs）和异质结；二维杂化有机-无机卤化铅钙钛矿（LHPs）。本研究的目的是通过实验探索俄歇复合如何依赖于能带结构、电子-声子耦合和空间约束，并定量地了解俄歇散射过程的微观机制。只要有可能，PIs将实施最直接的实验探针，例如，使用飞秒光谱学直接检测俄歇电子散射到特定的能量和动量空间，吸收/发射光谱来确定俄歇复合率作为空间限制和动量工程的函数，磁光谱学来识别和量化带电产物(极化子，trions，以及自旋极化如何影响俄歇复合速率。pi选择这两种模型系统是因为它们的电子结构可以在TMDCs的实空间和动量空间中进行控制。它们的能带结构对介电屏蔽、异质结的取向排列和外部磁场都很敏感。lhp被证明是光电子学领域最具吸引力的材料系统之一，它可以生长成二维纳米结构，通过卤化铅层的数量可以很容易地控制量子约束。此外，由于强自旋-轨道耦合（SOC）和局部对称反转的破坏，提出的Rashba效应可能允许外部电或磁控制能带结构。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 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.